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Foreword
There is a vast and often bewildering array of synthetic methods and reagents available to
organic chemists today. Many chemists have their own favoured methods, old and new, for
standard transformations, and these can vary considerably from one laboratory to another.
New and unfamiliar methods may well allow a particular synthetic step to be done more
readily and in higher yield, but there is always some energy barrier associated with their
use for the first time. Furthermore, the very wealth of possibilities creates an informationretrieval problem. How can we choose between all the altematives, and what are their real
advantages and limitations? Where can we find the precise experimental details, so often
taken for granted by the experts? There is therefore a constant demand for books on synthetic methods, especially the more practical ones like Organic Syntheses, Organic
Reactions and Reagents for Organic Synthesis, which are found in most chemistry laboratories. We are convinced that there is a further need, still largely unfulfilled, for a uniform
series of books, each dealing concisely with a particular topic from a practical point of
view - a need, that is, for books full of preparations, practical hints and detailed examples,
all critically assessed, and giving just the information needed to smooth our way painlessly
into the unfamiliar territory. Such books would obviously be a great help to research students as well as to established organic chemists.
We have been very fortunate with the highly experienced and expert organic chemists,
who, agreeing with our objective, have written the first group of volumes in this series,
Best Synthetic Methods. We shall always be pleased to receive comments from readers and
suggestions for future volumes.
A. R. K., O. M.-C., C. W. R.
Preface (1994 edition)
Tellurium is the fourth element of the VIA family of the periodic table, which starts with
oxygen. Since tellurium exhibits an electronic configuration similar to that of selenium and
sulphur, the chemical behaviour of these elements is obviously closely related. This similarity was a hindrance to the greater development of tellurium chemistry. During several
decades, research was restricted to an extrapolation of well-established reactions for the
preparation and use of organic sulphur compounds to selenium, and mainly from selenium
to tellurium.
Although over a quarter of a century ago it would not have been predicted that the
importance of the VIA family of the periodic table would exceed that of its second element, sulphur, the development of organoselenium chemistry has been so explosive that
little comment is necessary, as illustrated by the impressive number of papers as well as by
several books 1-3 on the field. Tellurium compounds have taken an even longer time to rise
from being considered an exotic and perverse element to a useful tool in organic chemistry.
In the mid-1950s, the German chemist Heinrich Rheinboldt reviewed the preparation
and reactivity of the organic tellurium compounds by comparison with selenium analogues
in Houben-Weyl-Methoden der Organischen Chemie, Vol. IX (1955). During the following years, two books and several review articles were published on the organic chemistry
of tellurium, but these were still within the areas of preparation and reactivity. It was in
1971 that the first "Symposium on the Selenium and Tellurium Chemistry" took place, and
since then symposia have been held every 4 years. In the last few years tellurium compounds have begun to be employed in organic synthesis, giving rise to a significant number of publications and to several review articles. Finally, in 1990, a Houben-Weyl volume
of more than 1000 pages was published coveting all aspects of tellurium chemistry (author,
K.Y. Irgolic).
At present the author feels that the remarkable development attained by the organotellurium chemistry is a clear reason for a monograph from the point of view of the organic
chemist.
The aim of this monograph is to provide a comprehensive overview of the preparation
and synthetic applications of tellurium compounds. It will focus on the preparation of
selected inorganic tellurium compounds and on the main classes of organotellurium compounds. The major interest of the volume probably resides in the use of these inorganic and
organic compounds as reagents in organic syntheses as well as the conversion of organotellurium into free organic compounds. In this regard it is sufficient to emphasize that
extremely useful reactions achieved with tellurium reagents, such as selective reductions
and oxidations of a large variety of organic functionalities, have not been mentioned until
now in textbooks specifically devoted to organic synthetic methodology.
This monograph is appropriate for chemists who, although not experts in tellurium
chemistry, have had a basic grounding to graduate level in organic chemistry and with sufficient experience of typical experimental operations.
vii
viii
PREFACE (1994 EDITION)
A considerable number of "experimental procedures" have been included. These have
been described in accordance with the original papers, and therefore the reader will find
significant differences in the description of these procedures, some rich and others very
poor in detail. In the last case, the practitioner who is used to overcoming the usual laboratory difficulties will need to use a certain degree of initiative.
The author will feel very gratified if this volume helps some chemists to become familiar with tellurium which up till now they may have considered only as a useless and
unpleasant dement.
N. Petragnani
REFERENCES
1. Klayman, D. L.; Gunther, W. H. H. (eds.). Organic Selenium Compounds: Their Chemistry and
Biology. Wiley, New York, 1973.
2. Paulmier, C. Selenium Reagents and Intermediates in Organic Synthesis. Pergamon Press,
Oxford, 1986.
3. Liotta, D. (ed.). Organoselenium Chemistry. Wiley, New York, 1987.
Preface
Over a decade after the publication of the first edition of this book, it is unnecessary to
emphasize once more the remarkable developments attained in organic tellurium chemistry.
Almost a thousand papers have been published in this last period, and numerous
research groups all over the world have consolidated their international status.
Undoubtedly tellurium chemistry can participate in several areas of organic chemistry,
as well as in others, and ever-more research chemists introduce tellurium to solve a wide
variety of problems.
All this seems to us to be a good reason to write this new edition of the book. It does
not differ in its general approach from the first one. Obviously it is not a compendium coveting exhaustively all the aspects of organic tellurium chemistry. For this purpose the
Irgolic E12b volume of Houben-Weyl is yet incomparable although 16 years old.
This book was devised in accordance with the intention of the Academic Press series
"Best Synthetic Methods" of the first edition, which is clearly focused in the foreword and
in the preface.
Several chapters such as vinylic tellurides, transmetallation reactions, coupling reactions and free-radical chemistry have been enriched and brought up to date with new
information related to their increased involvement in the most varied synthetic manipulations.
A chapter has been dedicated to heterocyclic compounds, covering the preparation and
reactivity of the most familiar members of the class.
Toxicology and pharmacology have also been briefly considered, and we are greatly
indebted with C. R. Nogueira, G. Zeni and J. B. T. Rocha for allowing us to use their recent
review (Chem. Rev. 2004, 104, 6255) as a source for our new chapter.
Probably some contributions have escaped our judgement and not been introduced in
this book. We apologize to any authors for the omission.
We would be gratified if this new edition, with its broad level of information, can disclose basic knowledge to the beginner in tellurium chemistry as well as furnish salient features for opening new perspectives to advanced researchers.
Nicola Petragnani and H61io A. Stefani
ix
Abbreviations
AIBN
CTAB
DIBAL-H
DME
DMSO
ee
ESR
GC-MS
HMPA
LICA
LiTMP
m-CPBA
MPLC
NBSP
NMP
NOESY
PTC
TBTH
TCNQ
TEMPO
TFA
TLC
TMEDA
TUDO
2,2'-Azo bisisobutyronitrile
Cetyl trimethylammonium bromide
Diisobutylaluminium hydride
1,2-Dimethoxyethane
Dimethyl sulfoxide
Enantiomeric excess
Electron spin resonance
Gas chromatography-mass spectrum
Hexamethylphosphoric acid triamide
Lithium isopropylcyclohexylamide
Lithium 2,2,6,6-tetramethylpiperidide
meta-Chloroperbenzoic acid
Medium pressure liquid chromatography
para-Nitrobenzenesulphonyl peroxide
N-methyl-2-pyrrolidinone
Nuclear overhauser enhancement spectroscopy
Phase transfer catalyst
Tributyltin hydride
7,7,8,8-Tetracy ano-pa ra-quinodimethane
2,2,6,6-Tetramethyl-l-piperidinyloxy free radical
Trifluoroacetic acid
Thin layer chromatography
N,N,N',N'-tetramethyl- 1,2-ethanediamine
Thiourea dioxide
XXV
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Introduction
1.1
SOME PHYSICAL PROPERTIES OF TELLURIUM
The Pauling electronegativities of carbon and tellurium are, respectively, 2.5 and 2.1. This,
in addition to the large volume of the tellurium atom (atomic radius 1.37, ionic radius
2.21), promotes easy polarization of Te–C bonds. The ionic character of the bonds
increases in the order C(sp3)⫺Te⬎C(sp2)⫺Te⬎C(sp)⫺Te, in accordance with the electronegativity of carbon accompanying the s character (Table 1.1).
The Te⫺C bond therefore exhibits a high reactivity, as demonstrated typically by the
easy heterolytic cleavage towards nucleophilic reagents.
1.2
RELEVANT MONOGRAPHS AND REVIEW ARTICLES
1. Rheinboldt, H. in Houben-Weyl-Methoden der Organischen Chemie (ed. E. Muller). 4th edn,
Vol. IX. Georg Thieme, Stuttgart, 1955.
2. Petragnani, N.; Moura Campos, M. Organomet. Chem. Rev. 1967, 2, 61.
3. Cooper, W. C. (ed.). Tellurium. Van Nostrand Rheinhold, New York, 1971.
4. Irgolic, K. J.; Zingaro, R. in Organometallic Reactions (eds. E. Becker; M. Tsutsui). Wiley, New
York, 1971.
5. Irgolic, K. J. The Organic Chemistry of Tellurium. Gordon and Breach, New York, 1974.
6. Irgolic, K. J. J. Organomet. Chem. 1975, 103, 91. lrgolic, K. J. J. Organomet. Chem. 1977, 130,
411. Irgolic, K. J. J. Organomet. Chem. 1978, 158, 235; Irgolic, K. J. J. Organomet. Chem.
1980, 189, 65. Irgolic, K. J. J. Organomet. Chem. 1980, 203, 368.
Table 1.1
Some physical properties of the VIA family of elements
Element Atomic
number
Atomic Electronic
mass
configuration
O
S
Se
Te
15.99
32.06
78.96
127.6
8
16
34
52
1s22s22p4
2s22p63s23p4
3s23p63d104s24p4
4s24p64d105s25p4
1
Pauling
Ionization
electronegativity potential
Ionic
radius
Atomic
radius
3.5
2.5
2.4
2.1
1.40
1.84
1.98
2.21
0.66
1.04
1.17
1.37
13.61
10.36
9.75
9.01
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1. INTRODUCTION
7. Uemura, S. Nippon Kagaku Kaishi 1981, 36, 381.
8. Petragnani, N.; Comasseto, J. V. Proceedings of the 4th International Conference of the Organic
Chemistry of Selenium and Tellurium (eds. F. Y. Berry; W. R. McWhinnie), pp. 98–241. The
University of Aston in Birmingham, Birmingham, 1983.
9. Uemura, S. J. Synth. Org. Chem. Jpn. 1983, 41, 804.
10. Engman, L. Acc. Chem. Res. 1985, 18, 274.
11. Petragnani, N.; Comasseto, J. V. Synthesis 1986, 1.
12. Suzuki, H. Synth. Org. Chem. Jpn. 1987, 45, 603.
13. Sadekov, D.; Rivkin, B. B.; Minkin, V. Y. Russ. Chem. Rev. 1987, 56, 343.
14. Patai, S.; Rappoport, Z. (ed.). The Chemistry of Organic Selenium and Tellurium Compounds,
Vols I and II. Wiley, New York, 1986, 1987.
15. Engman, L. Phosphorus Sulfur 1988, 38, 105.
16. Irgolic, K. Y. Houben-Weyl Methods of Organic Chemistry (ed. D. Klamann). 4th edn, Vol. E12b.
Georg Thieme, Stuttgart, 1990.
17. Petragnani, N.; Comasseto, J. V. Synthesis 1991, 793.
18. Petragnani, N.; Comasseto, J. V. Synthesis 1991, 897.
19. Petragnani, N. Tellurium in Comprehensive Organometallic Chemistry II (ed. A. McKillop).
Vol. 11, Chapter 14. Pergamon, Elsevier, 1995.
20. Comasseto, J. V.; Lo, W. L.; Petragnani, N.; Stefani, H. A. Synthesis 1997, 4, 373.
21. Petragnani, N.; Stefani, H. A. Tetrahedron 2005, 61, 1613.
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Preparation of the More Important
Inorganic Tellurium Reagents
2.1
TELLURIUM TETRACHLORIDE
Tellurium tetrachloride is prepared directly from the respective elements.1
Te + 2Cl2
TeCl4
Experimental procedure1. The apparatus in Figure 2.1 is charged with 100–150 g of finepowdered Te (the apparatus and the Te have been previously heated overnight at 110°C to
ensure dryness). A stream of Cl2 (dried by bubbling in concentrated H2SO4) is slowly introduced by means of a Tygon tube; meanwhile, the apparatus is heated with a small burner
flame. After a few minutes the solid Te begins to be converted into a black liquid. The reaction is exothermic (and proceeds spontaneously), but the absorption of Cl2 is accelerated
by heating the mixture from time to time. After a while the mixture becomes clearer,
giving finally an amber-coloured liquid, which by increased heating forms a vapour of the
Figure 2.1 Apparatus to prepare TeCl4.
3
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2. PREPARATION OF THE MORE IMPORTANT INORGANIC TELLURIUM REAGENTS
same colour. At that time the absorption is complete and all the Te has been converted into
TeCl4. By vigorous burner heating, the product is transferred by distillation, under a continuous Cl2 stream, into the tubes, where it solidifies. The tubes are detached from the
apparatus by melting. The yield is 90%.
Tellurium tetrachloride is a pale yellow crystalline solid, melting point (m.p.) 225°C,
highly hygroscopic, soluble in dioxane, acetone, ether, methanol and ethanol but less soluble in benzene and chloroform.
Tellurium tetrachloride is instantaneously hydrolysed by water, giving tellurium
oxochloride, which is soluble in concentrated hydrochloric acid, forming HTeCl5 and
H2TeCl6.
TeCl4 + H2O
TeOCl2 + 2HCl
The Raman data suggest the ionic structure for TeCl3⫹ Cl⫺ in both the solid and liquid
states.2
2.2
TELLURIUM DIOXIDE
Tellurium dioxide is prepared by oxidation of elemental tellurium with concentrated nitric
acid.3
Te
conc. HNO3
2TeO2 . HNO3
400°C
TeO2
Experimental procedure.3 Commercial Te (20 g, finer than 60 mesh) is weighed into a
1000 mL beaker, covered with H2O (200 mL) and treated by the slow addition of 95 mL
of concentrated HNO3 (95 mL, specific gravity 1.42). The reaction is allowed to continue
for 5–10 min with occasional agitation. Insoluble impurities are removed immediately by
filtration on a Büchner funnel. The filtrate is transferred to a 600 mL beaker. Concentrated
HNO3 (65 mL) is then added and the solution boiled until oxides of nitrogen have been
expelled. Basic nitrates of antimony and bismuth precipitate at this point if these substances are present as impurities. These are removed by filtering through asbestos, after
which the clear liquor is evaporated gently on a water bath under a hood in an open 600
mL beaker. Basic tellurium nitrate is deposited. The evaporation is continued until the
solution volume has been reduced to 100 mL. The solution is then cooled. The crystalline
deposit is filtered, washed with H2O on a suction filter and air dried. The dry crystals are
placed in a 400 mL beaker, covered by inverting a 1000 mL beaker over the smaller beaker,
and heated at a hot-plate temperature of 400–430°C for 2 h. The TeO2 (21 g, 84%)
is cooled and bottled immediately to avoid slow darkening due to reduction by organic
matter from the atmosphere.
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ALKALI METAL TELLURIDES (Te2⫺Cat2⫹)
5
Tellurium dioxide is a white solid existing in two crystalline forms. It is soluble in water
and in both aqueous sodium hydroxide and hydrochloric acid.
2.3
⫺
⫹
ALKALI METAL TELLURIDES (Te2⫺
Cat2⫹
)
These reagents are usually prepared in situ.
The preparative methods are outlined in sequence and representative experimental procedures are described in later chapters.
2.3.1
From the elements (2Na + Te → Na2Te)
2.3.1.1
In liquid ammonia4
2.3.1.2
In DMF5
2.3.1.3
In the presence of naphthalene6
2.3.2
From tellurium and reducing agents (Te → Te2−−)
2.3.2.1
Rongalite (HOCH2SO2Na/NaOH )7
2.3.2.2
Thiourea dioxide (TUDO, HN=C(NH2)S(O)OH)/NaOH8
2.3.2.3
Hydride transfer reagents
KBH4/NaOH9
Me4NBH4 (giving tetramethylammonium telluride)10
NaBH4/DMF11
NaBH4/H2O12
LiHBH313
2.3.2.4
Tin(II) chloride/KOH/DMSO14
2.3.2.5
Hydrazine hydrate/NaOH15
2.3.3
From tellurium and non-reducing bases
2.3.3.1
NaH/DMF16
2.3.3.2
NaH/DME17
2.3.3.3
NaH/N-methyl-2-pyrrolidone18
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2. PREPARATION OF THE MORE IMPORTANT INORGANIC TELLURIUM REAGENTS
2.4
2.4.1
ALKALI METAL DITELLURIDES (Na2Te2)
From the elements (2Na + 2Te → Na2Te2)
2.4.1.1
In liquid ammonia19
2.4.1.2
In HMPA20
2.4.1.3
In the presence of naphthalene21
2.4.2
red
⫺
From tellurium and reducing agents (2Te → Te22⫺
)
2.4.2.1
Rongalite22
2.4.2.2
TUDO/NaOH23
2.4.2.3
Hydride transfer reagents
NaBH4/EtONa/EtOH24
NaBH4/DMF25
2.4.2.4
Hydrazine hydrate/NaOH26
2.5
HYDROGEN TELLURIDE (H2Te)
Hydrogen telluride is prepared in situ by hydrolysis of aluminium telluride.27
Al2Te3 + 3H2O → 3TeH2 + Al203
2.6
SODIUM HYDROGEN TELLURIDE (NaHTe)
Sodium hydrogen telluride is prepared by reduction of tellurium with NaBH4 under several conditions. The original procedure uses ethanol as the solvent, adding, after complete
reduction of the tellurium, an appropriate amount of acetic acid (see Section 4.1.2, ref. 10;
Section 4.1.7, ref. 29).
REFERENCES
1.
2.
3.
4.
Suttle, Y. F.; Smith, C. R. F. Inorg. Synth. 1956, III, 140.
Gerding, H.; Houtgraff, H. Recl. Trav. Chim. 1954, 73, 737.
Marshall, H. Inorg. Synth. 1950, III, 143.
Section 3.1.1.1 (a), ref. 1.
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7
5. Section 3.1.1.1 (a), ref. 8.
6. Section 3.1.1.1 (a), refs. 10, 11.
7. Section 3.1.1 1 (b), refs. 14, 15; Section 4.1.6, ref. 19; Section 4.1.9, ref. 33; Section 4.1.11, ref.
41; Section 4.2.5, ref. 6.
8. Section 3.1.1.1 (b), ref. 23.
9. Section 3.1.1.1 (b), ref. 24.
10. Section 3.1.1.1 (b), ref. 15.
11. Section 3.1.2.2, ref. 8; Section 4.1.11, ref. 40; Section 4.3.1.1, ref. 2.
12. Section 3.1.3.1, ref. 1; Section 4.1.13.1, ref. 49.
13. Section 5.1, ref. 2.
14. Section 3.1.1.1 (b), ref. 26.
15. Section 3.1.1.1 (b), ref. 27.
16. Section 3.1.2.1, ref. 5; Section 3.16.1.3, ref. 27; Section 4.1.5, ref. 17; Section 4.2.1, ref. 1;
Section 4.3.2.2, ref. 5.
17. Section 4.2.5, ref. 5.
18. Section 3.1.2.1, ref. 7.
19. Section 3.2.1.1, ref. 1.
20. Section 3.2.1.2, ref. 10.
21. Section 3.2.1.1, ref. 3.
22. Section 3.2.1.1, ref. 6.
23. Section 3.2.1.1, ref. 7.
24. Section 3.2.1.1, ref. 5.
25. Section 4.3.1.1, ref. 2.
26. Section 3.2.1.1, ref. 9.
27. Section 4.1.1.1, ref. 1; Section 4.1.4, ref. 14; Section 4.1.6, ref. 18.
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Preparation of the Principal Classes of
Organic Tellurium Compounds
This chapter is devoted mainly to the preparation of those classes of organotellurium compounds that have been more systematically investigated in past years, owing to their peculiar role as reagents or intermediate in organic synthesis, including compounds of
structural, biological or theoretical interest.
Sections 3.1–3.3 outline the principal preparative methods of diorganyl tellurides and
ditellurides, organyltellurium trichlorides and diorganyltellurium dichlorides, which
were the first classes of compounds investigated at the beginning of tellurium organic
chemistry.
The physical properties and stability of the compounds are also described briefly.
DIORGANYL TELLURIDES (SECTION 3.1)
The main routes to symmetrical diorganyl tellurides involve the direct reaction of nucleophilic telluride dianions (usually as Na2Te) with alkylating or arylating reagents.
Otherwise the electrophilic tellurium tetrahalides react with arylmagnesium reagents,
giving diaryl tellurides.
Unsymmetrical tellurides are obtained as follows:
•
•
•
starting from nucleophilic tellurolate anions (easily generated by telluration of
Grignard and lithium reagents or by reduction of diorganyl ditellurides) by reaction
with alkylating or arylating reagents, or by addition to acetylenes;
by cleavage of diaryl ditellurides with arylmagnesium reagents, diazonium salts, or
arenesulphonylazo compounds;
by the reaction of electrophilic tellurenyl halides with Grignard reagents.
9
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3. PREPARATION OF THE PRINCIPAL CLASSES OF ORGANIC TELLURIUM
2RX
RTeR
2ArX
Te2-
ArMgX (exc.)
ArTeAr
[2ArN2+]XRX.R1X
R1X
RTeR1
RTe-
RX
Ar-
ArTe-
R-
Te
R(Ar)Te
R(Ar)
ArTeR
TeX4
Te
NaBH4
R-
Na (Li)
[ArTeX]
Ar1X
R(Ar)
ArTeTeAr
X2
Ar1ArTeAr1
[Ar1N2+]XAr1N = NSO2Ar
Diorganyl tellurides have low molecular mass and are colourless or yellowish liquids with
an unpleasant and penetrating odour. Dimethyl telluride is a metabolite of tellurium and tellurium compounds in a variety of living organisms, including humans. Higher dialkyl tellurides
and most diaryl tellurides are solids with low melting points (diphenyl telluride is a liquid).
Diorganyl tellurides are soluble in common organic solvents.
Because of the above-mentioned organoleptic properties, it is recommended that contact
between dialkyl tellurides and the skin is avoided, and that, in general, all work involving
diorganyl tellurides is performed under a well-ventilated hood.
The thermal stability and sensitivity to the atmosphere of diorganyl tellurides is dependent
on the organic moiety. Many aliphatic, cycloaliphatic, as well as vinylic and acetylenic tellurides are reported to be decomposed by light, and therefore some authors recommend preparation of these compounds in the dark or under a red light.1 These tellurides are also sensitive
to exposure to the open atmosphere, easily undergoing oxidation to mixtures containing the
corresponding telluroxides in addition to other products. These oxidations are especially effective in solution, where the oxidation products separate as amorphous insoluble solids. Benzyl
groups in tellurides are characterized by a peculiar lability, as demonstrated by the oxidative
cleavage of aryl benzyl tellurides leading to aromatic carbonyl compounds.2 Diaryl tellurides
are generally more stable and can be handled in the open atmosphere.
DIORGANYL DITELLURIDES (SECTION 3.2)
Diorganyl ditellurides are prepared by three routes:
•
•
alkylation or arylation of the ditelluride dianion (usually as Na2Te2);
oxidation of tellurolate anions;
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ORGANYLTELLURIUM TRICHLORIDE AND DIORGANYLTELLURIUM DIHALIDES
•
11
reduction of the corresponding organyltellurium trichlorides.
red.
2RX
RTeTeR
Te222ArX
ArTeTeAr
RTeCl3
R-
ox.
RTe-
ox.
ArTe-
red.
ArTeCl3
Ar-
Te
The Te2 group is a chromophore, and aliphatic and aromatic ditellurides exhibit a characteristic orange to pale or dark red colour (absorption maximum at ~400 nm).
The short-chain aliphatic ditellurides are liquids with a pungent odour, whereas the
higher members (more than 10 C chains) are solids with low melting points.
Diaryl ditellurides, which are more important as synthetic intermediates, are solids,
highly soluble in solvents such as petroleum ether, benzene, chloroform, ether, and tetrahydrofuran (THF), but are less soluble in methanol and ethanol.
Dibenzyl ditelluride exhibits the peculiar lability of the tellurium–benzyl bond already
mentioned for the corresponding tellurides. By heating the solid at 120°C, or by exposure
in solution to ordinary incandescent lighting or to a Hanovia lamp, a rapid decomposition
into elementary tellurium and dibenzyl telluride occurs.3
ORGANYLTELLURIUM TRICHLORIDE AND DIORGANYLTELLURIUM
DIHALIDES (SECTIONS 3.5 AND 3.9)
Organyltellurium trichlorides and diorganyltellurium dichlorides are prepared starting
from the electrophilic tellurium tetrachloride (or aryltellurium trichlorides) by:
•
•
•
•
condensation reactions with active methylene compounds;
addition to a C⫽C bond (or a C⬅C bond, not shown in the scheme);
electrophilic substitution in aromatic hydrocarbons; and
reaction with organomercury chlorides.
Organyltellurium trichlorides and the not directly accessible tribromides and triiodides
are obtained by the halogenolysis of the Te–Te bond of the corresponding ditellurides.
Diorganyltellurium dihalides can also be prepared by the addition of halogens to the
parent tellurides.
R
TeCl3
R
Y
R
or
Y
Y
Cl
Cl
or
)2 TeCl2
TeCl3
TeCl4
ArH
ArHgCl
ArTeCl3
)2 TeCl2
ArH
Ar2TeCl2
ArHgCl
Ar1HgCl
ArAr1TeCl2
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ArTeCl2
R
ArTeCl3
Ar1H
Y
R
Y
ArAr1TeCl2
Cl
ArTeCl2
ArTeTeAr
3X2
red
ArTeAr
X2
2ArTeX3
X = Cl, Br, I
Ar2TeX2
red
The tri- and dihalides are crystalline compounds. The chlorides are colourless (or yellow
such as some aryltellurium trichlorides), the colour changing to orange and red (or deep
red) for the bromides and iodides.
The aryltellurium trihalides are generally more stable than the alkyltellurium trihalides
(alkyltellurium trichlorides, produced by the addition of TeCl4 to olefins, easily liberate
elemental tellurium).
The reactivity of aryltellurium trihalides decreases on going from the chlorides to the
iodides, the same trend occurring for hydrolysis. Aryltellurium trichlorides are very sensitive to water and moisture and are easily hydrolysed, the tribromides being more stable,
while the triiodides are unaffected by cold water and can be prepared even by aqueous procedures. Diaryltellurium dihalides are stable in water, and ionic exchange reactions allow
the conversion of dichlorides into dibromides and diiodides.
Aryltellurium trichlorides are highly soluble in methanol and ethanol but less soluble in
benzene. Diaryltellurium dichlorides exhibit inverse solubilities, being more soluble in
benzene than in methanol or ethanol. These properties allow an easy separation of diaryl
tellurides from diaryl ditellurides (frequently formed as by-products in the preparation of
tellurides): the mixture is treated with SO2Cl2 and the obtained mixed di- and trichlorides
are separated by the appropriate solvents, and reduced back into the pure tellurides and
ditellurides.
REFERENCES
1. Clive, D. L. J.; Chittattu, G. J.; Farina, V.; Kiel, W. A.; Menchen, S. M.; Russell, C. G.; Singh,
A.; Wong, C. K.; Curtis, N. J. J. Am. Chem. Soc. 1980, 102, 4438.
2. Ferreira, J. T. B.; Oliveira, A. R. M.; Comasseto, J. V. Tetrahedron Lett. 1992, 33, 915.
3. Spencer, H. K.; Cava, M. P. J. Org. Chem. 1977, 42, 2937.
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DIORGANYL TELLURIDES
3.1
13
DIORGANYL TELLURIDES
Diorganyl tellurides, compounds with two organic groups linked to a tellurium atom,
constitute the most abundant and familiar class of organic tellurium compounds. The
organic groups, of the most differentiated types, can be identical or different, giving rise to
symmetrical or unsymmetrical tellurides.
Since symmetrical dialkyl and diaryl tellurides are the most employed in organic synthesis, and often exhibit structural or biological interest, their preparation will be examined in detail, focusing on the methods and procedures that are considered as the most
popular.
3.1.1
3.1.1.1
Symmetrical dialkyl tellurides
From alkali tellurides and alkylating agents
Te2- + 2RX
RTeR
Alkali tellurides, among which sodium telluride is the most widely employed, are powerful nucleophilic reagents and therefore react easily with alkylating agents.
(a) From sodium telluride prepared from the elements
(i) Sodium/liquid ammonia method
Te + 2Na
NH3 liquid
Na2Te
RX
RTeR
This method has been applied successfully to n- and s-alkyl halides.1–4
Dialkyl tellurides (general procedure).1 Elemental Te is added in ~0.5 g portions to a wellstirred solution of Na in liquid NH3 until the solution decolourizes, forming a colourless
suspension (2 g-atom Na/1 g-atom Te). The quantities of the materials are chosen to give
a suspension of ~0.7 M. The alkylating agent is added dropwise in 10% excess to the
suspension of Na2Te. The reaction mixture is stirred until the NH3 evaporates. H2O is then
added, the mixture extracted with ether and the ethereal solution worked up in the usual
manner.
Diethyltelluride: yield 80%; b.p. 38°C/14 torr, Diisopropyltelluride: yield 80%;
b.p. 49°C/14 torr.
When the alkylating agent is insoluble in liquid ammonia, as in the case of long-chain
compounds, an organic solvent is added to the sodium telluride residue after evaporation
of the ammonia. Some cyclic and steroidal tellurides have been prepared from sodium telluride in ethanol and the appropriate dihalides.5–7
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3. PREPARATION OF THE PRINCIPAL CLASSES OF ORGANIC TELLURIUM
Sodium/DMF method 8,9
Te + 2Na
DMF
Na2Te
RX
RTeR
O O
Bis(2-phenyl-1,2-dioxolan-2-yl)methyl telluride (R⫽Ph–C–CH2) (typical procedure).8
Finely powdered Te (0.30 g, 2.3 mmol) and Na (0.22 g, 9.6 mmol) are stirred under N2 in
dry DMF (15 mL) at 110°C until all the Te has disappeared (15 min). 2-(Bromomethyl)2-phenyl-1,3-dioxolane (1.15 g, 4.7 mmol) in dry THF (10 mL) is added to the resulting
yellowish suspension. After 2.5 h at room temperature the reaction mixture is poured into
H2O and extracted with ether. Chromatography on SiO2 (eluent: CH2Cl2/petroleum ether
at 40–60°C, 1:1) furnishes the telluride (0.65 g (60%); recrystallized from EtOH, m.p.
67–68°C).
Additional examples: R ⫽ n-C12H25 (66%), PhCH⫽CH- (41%).9
(iii) Sodium/naphthalene method
Sodium telluride can be prepared under mild conditions from the elements in the presence
of catalytic amounts of naphthalene10 or by treating tellurium with sodium naphthalide.11
Te
Na / naphthalene
RX
Na2Te
RTeR
THF
(60-90%)
R = Et, n- Pr, n - Bu, MeOCH2CH2
Dialkyl tellurides (general procedure).10 Te powder (3.58 g, 28 mmol), Na chips (1.29 g,
56 mmol), and naphthalene (0.72 g, 5.6 mmol) in THF (25 mL) are refluxed under N2 and
stirred for 3 h. The heterogeneous white mixture is cooled at 0°C and the alkyl halide
(56 mmol) is added slowly, stirring for 30 min. After 30 min of additional stirring, the
mixture is filtered, the solution evaporated and the residue distilled under vacuum, giving
the telluride.
Diallyl telluride (typical procedure).11 In a 25 mL Schlenk flask, Te pieces (6.1 g, 48
mmol, from a Te ingot), Na (2.2 g, 96 mmol) and naphthalene (0.1 g, 0.8 mmol) in THF
(20 mL) are stirred under argon at 25°C for 4 days. The mixture is filtered and the filter
cake washed with THF (20 mL) and dried under vacuum to give Na2Te (7.6 g, 92%).
Alternatively, Te powder (60 mesh) and sodium naphthalide (2 mol equiv) are stirred in
THF for 4 h. Na2Te is isolated as an amber-coloured solid. The Na2Te (62.9 g, 0.362 mmol)
is slurried in absolute EtOH (400 mL). The slurry is cooled at 0°C and allyl bromide (93.3 g,
0.77 mmol) is added dropwise during a 1-h period while stirring. The mixture is stirred
for an additional hour at 20°C and then filtered. The grey filter cake is washed with EtOH
(400 mL). The combined washing and filtrate are evaporated at atmospheric pressure.
The residue is distilled, giving diallyl telluride as a pungent, air-sensitive, yellow liquid
(56.7 g (75%); b.p. 70–72°C/13 torr).
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DIORGANYL TELLURIDES
15
(b) From alkali tellurides prepared from tellurium and reducing agents
(i) Rongalite (sodium formaldehyde sulphoxylate) method
This method was first described at the beginning of the past century,12 and continues to
find a wide application.
Te
HOCH2SO2Na
NaOH / H2O
Na2Te
RX
RTeR
n-Alkyl halides, benzyl chloride, ethyl sulphate, and s-alkyl bromides give
the expected tellurides in medium yields whereas t-butyl chloride is not converted into the
telluride.13–15 Owing to the insolubility of the alkyl halides, ethanol must be added to
the reaction mixture.
Dibenzyl telluride (typical procedure).15 Rongalite (18.0 g, 0.5 mol) is added under N2 at
80°C to a suspension of Te (2.56 g, 20 mmol) in a solution of NaOH (12 g, 0.3 mol) in 125
mL of H2O. After stirring for 1 h, a solution of benzyl chloride (1.26 g, 10 mmol) in a small
volume of EtOH is added dropwise at room temperature to the almost colourless telluride
solution. After stirring for an additional hour, the mixture is extracted with ether, and the
ethereal solution dried (MgSO4) and evaporated. The residue is recrystallized from petroleum ether (40–60°C) under red light, giving the telluride as yellow needles (1.09 g (70%);
m.p. 49–57°C).
Cyclic tellurides, 16–18 including some with a steroidal structure,19,20 have been prepared
by the Rongalite method.
Te
( )n
Te
Te
Y
Y = 0, S
n = 1, 2
(ii) Sodium dithionite and thiourea dioxide method
The use of sodium dithionite (Na2S2O4) and thiourea dioxide (TUDO; HN⫽C(NH2)S(O)OH)
has been introduced later as a reducing agent for the preparation of sodium telluride in an
aqueous medium, followed by reaction with n-alkyl halides to give dialkyl tellurides.21,22
The TUDO method has been reinvestigated and has found wide use because of the simplicity of the experimental conditions.23
TUDO
RX
Na2Te
THF (CTBA) RTeR
NaOH / H2O / THF
(72 - 85%)
R = n- C12H23, n- C8H17, i- C3H7CH2CH2, THPO(CH2)6
Te
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3. PREPARATION OF THE PRINCIPAL CLASSES OF ORGANIC TELLURIUM
Dialkyl tellurides (general procedure).23 A mixture of TUDO (0.2 g, 2 mmol), NaOH
(0.112 g, 2.6 mmol), Te powder (0.128 g, 1 mmol) in H2O (0.75 mL) and THF (0.75 mL)
is refluxed for 1 h. The alkyl halide (2 mmol) and (cetyl trimethyl ammonium bromide)
CTBA (0.004 g, 1.1 ⫻ 10⫺5 mmol) in THF (0.5 mL) are added to the pale pink solution.
After 1 h of additional reflux the mixture is worked up in the usual manner and the residue
purified by column chromatography on SiO2 (elution with petroleum ether 40–60°C).
(iii) Hydride transfer reagent method
A useful method for the reductive conversion of elemental tellurium into Te2⫺ anions
employs complex hydrides such as sodium or potassium borohydride and tetraalkyl
ammonium borohydride as reducing agents.
Te
cat+BH42solvent / reflux Te
cat = Na
+,
K+,
RX
RTeR
N+
Me4
Di-n-octyl telluride (typical procedure).24 Elemental Te (2.54 g, 20 mmol) is heated at reflux
in 20% aqueous NaOH (43 mL) containing KBH4 (2.7 g, 50 mmol), under argon. After 1.5
h the mixture is deep purple, but after an additional 30 min of reflux turns pale yellow and
no Te metal remains. Bromooctane (7.72 g, 40 mmol) in MeOH (50 mL) is added, the solution refluxed for 30 min, cooled, poured into H2O (100 mL) and extracted with ether (3⫻).
The ether extracts are washed with H2O, dried (Na2SO4) and evaporated. The oily residue is
distilled under vacuum, giving the telluride (5.5 g (78%); b.p. 154°C/0.7 torr).
Dibenzyl telluride (typical procedure).15 Elemental Te (1.27 g, 10 mmol) and Me4NBH4
(1.78 g, 20 mmol) are heated in H2O (100 mL) in a steam bath under N2 until the initially
produced purple colour is discharged. After cooling at room temperature, benzyl chloride
(2.53 g, 20 mmol) in EtOH (20 mL) is added slowly with stirring and rigorous exclusion
of air. After 2 h of stirring, the mixture is extracted with ether, dried and evaporated. The
residue is recrystallized from petroleum ether (under red light), giving the telluride as yellow needles (2.56 g (82%); m.p. 49–57°C).
In an interesting one-pot procedure the borohydride is used as both the reducing and
alkylating agent.25
Te + 2R4NBH4
RTeR + 2R3NBH3 + H2
Di-n-butyl telluride (typical procedure).25 Elemental Te (0.63 g, 5 mmol) and n-Bu4NBH4
(3.87 g, 15 mmol, 50% excess) are refluxed in toluene (80 mL) under N2 and stirring. The
initial red solution gradually turns colourless, giving a clear solution after 3 h. The cooled
solution is washed with H2O (50 mL) and 1 M HCl (50 mL) (evolution of H2). The organic
phase is dried (CaCl2) and evaporated, giving an oil (mixture of the telluride and
Bu3NBH3). The telluride is separated by column chromatography on SiO2 (eluent:
CH2Cl2/petroleum ether at 40–60°C, 1:1) (1.20 g (95%); nD20⫽1.5165).
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DIORGANYL TELLURIDES
17
(iv) Tin(n)/potassium hydroxide method 26
Te
SnCl2 / KOH
DMSO, 120°C, 10h
K2Te
MeI
MeTeMe
Dimethyl telluride (typical procedure).26 KOH (100 g, 1.78 mol) in dimethyl sulfoxide
(DMSO) (180 mL) is heated on a steam bath. SnCl2 (10 g, 53 mmol) and Te powder
(60 g, 0.47 mmol) are added and the mixture heated at 120°C for 20 h. After cooling at 40°C,
methyl iodide (157 g, 1.1 mol) is added dropwise for 2 h. The mixture is then heated at
70°C for 2 h and then distilled until the condensing vapour reaches a temperature of
100°C. The organic layer of the residue is separated, dried and distilled (71.6 g (97%);
b.p. 93–94°C).
(v) Hydrazine hydrate method 27
N2H4 / NaOH
RX
Na2Te
RTeR
(55 - 73%)
DMF
R = Et, n- Bu, n- pentyl, s- Bu, i - pr - CH2CH2, n - octyl
Te
Dibutyl telluride (typical procedure).27 Hydrazine hydrate 80% (0.50 mL, 7.1 mmol) is
added dropwise using a syringe to a stirred mixture of finely ground Te (0.64 g, 5 mmol)
and powdered NaOH (0.40 g, 10 mmol) in DMF (10 mL) at 50–60°C. After 3 h stirring,
n-butyl bromide (1.4 g, 10 mmol) in DMF (2 mL) is added, the mixture is heated at 60°C
for a further 30 min, cooled at room temperature and extracted with petroleum ether
(40–60°C). The organic phase is separated, washed with H2O, dried (CaCl2) and evaporated, giving the pure telluride (0.69 g (57%); b.p. 111–114°C/13 torr).
3.1.1.2
From bis(triphenylstannyl) telluride and alkylating reagents
The title reagent (prepared by the reaction of sodium hydrogen telluride with chlorotriphenylstannane)28 reacts easily with the more active halides such as benzyl bromides whereas
common halides need to be activated by cesium fluoride.29
Alkyl iodides and bromides react satisfactorily under these conditions whereas alkyl
chlorides and aryl halides are nonreactive.
Ph3SnTeSnPh3 + RX
MeCN
THF
PH3Sn TeSnPh3
R X
-Ph3SnF
F..
PH3Sn TeR
R X
40 - 100%
RTeR + Ph3SnF
F..
RX = BzBr, n - C10H21I, n - C10H21Br, i - PrI, EtO2CCH2Br, PhCOCH2Br,
Cl(CH2)6Br (giving [Cl(CH2)6]2Te),
Br
Br
giving
Te
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3. PREPARATION OF THE PRINCIPAL CLASSES OF ORGANIC TELLURIUM
Dialkyl tellurides (general procedure).29 Bis(triphenylstannyl) telluride (1 equiv), alkyl
halide (2 equiv), excess CsF (4 equiv) and the solvent (MeCN or MeCN/THF) are mixed,
kept under N2 and monitored by thin layer chromatography (TLC) (or 1H NMR). Usual
work-up of the mixture yields the telluride.
REFERENCES
1. Brandsma, L.; Wijers, H. E. Recl. Trav. Chim. Pays-Bas 1963, 82, 68.
2. Sukhai, R. S.; Jong, R. A.; Verkruijsse, H. D.; Brandsma, L. Recl. J. R. Neth. Chem. Soc. 1981,
100, 368. Sukhai, R. S.; Jong, R. A.; Verkruijsse, H. D.; Brandsma, L. Chem. Abstr. 1982, 96,
104204.
3. US 2398414 (1946), Cal Research Corporation; Denison, G. H.; Condit, P. C. Chem. Abstr.
1946, 40, 3598.
4. Bogolyubov, G. M.; Shlyk, Y. N.; Petrov, A. A. J. Gen. Chem. USSR 1969, 39, 1768 (in English).
5. Buchta, E.; Greiner, K. Chem. Ber. 1961, 94, 1311.
6. Zanati, G.; Wolf, M. E. J. Med. Chem. 1972, 15, 368.
7. Zanati, G.; Gaare, G.; Wolf, M. E. J. Med. Chem.1974, 17, 561.
8. Engman, L. Organometallics 1986, 5, 427.
9. Ohe, K.; Takahashi, H.; Uemura, S.; Sugita, N. Nippon Kagaku Kaishi 1987, 1469.
10. Bhasin, K. K.; Gupta, V.; Gautam, A.; Sharma, R. P. Synth. Commun. 1990, 20, 2191.
11. Higa, K.; Harris, D. C. Organometallics 1989, 8, 1674.
12. Tschugaeff, L.; Chlopin, W. Ber. Dtsch. Chem. Ges. 1914, 47, 1274.
13. Balfe, M. D.; Nandi, K. M. J. Chem. Soc. 1941, 70.
14. Balfe, M. P.; Chaplin, C. A.; Phillips, H. J. Chem. Soc. 1938, 344.
15. Spencer, H. K.; Cava, M. P. J. Org. Chem. 1977, 42, 2937.
16. Farrar, W. V.; Gulland, J. M. J. Chem. Soc. 1945, 11.
17. McCullough, J. B. Inorg. Chem. 1965, 4, 862.
18. Holliman, F. G.; Mann, F. G. J. Chem. Soc. 1945, 37.
19. Knapp Jr., F. F. J. Labelled Compd. Radiopharm. 1980, 17, 81.
20. Suginome, H.; Yamada, S.; Wang, J. B. J. Org. Chem. 1990, 55, 2170.
21. Brigov, B. G.; Bregadze, V. I.; Golubinskaya, L. N.; Tonoyan, L. G.; Kozyzkin, B. I. USSR 541,
851, Chem. Abstr. 1977, 87, 5394.
22. Kozyzkin, B. I.; Salamtin, B. A.; Ivanov, L. L.; Kuzovlev, I. A.; Gribov, B. G.; Federov, V. A. Poluch.
Anal. Veshchestv Osoboi Chist [Dokl. Vses. Konf.] 1976, 5, 142, Chem. Abstr. 1979, 91, 140278.
23. Ferreira, J. T. B.; Oliveira, A. R.; Comasseto, J. V. Synth. Commun. 1989, 19, 239.
24. Kirsch, G.; Goodman, M. M.; Knapp Jr., F. F. Organometallics 1983, 2, 357.
25. Bergman, J.; Engman, C. Synthesis 1980, 569.
26. Voronkov, M. G.; Stankevich, V. K.; Rodkniko, P. A.; Korchevin, N. A.; Deryagina, E. N.;
Trofimov, B. A. J. Gen. Chem. USSR 1987, 57, 2398.
27. Lue, P.; Chen, B.; Yu, X.; Chen, J.; Zhou, X. Synth. Commun. 1986, 16, 1849.
28. Einstein, F. W.; Jones, C. H. W.; Jones T.; Sharma, R. D. Can. J. Chem. 1983, 61, 2611.
29. Li, C. J.; Harpp, D. N. Tetrahedron Lett. 1990, 31, 6291.
3.1.2
3.1.2.1
Symmetrical diaryl tellurides
From sodium telluride and non-activated aryl halides
The normal low reactivity of aryl halides towards nucleophilic reagents is not generally
observed in their reaction with alkali tellurides. The observed reactivity seems to be
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DIORGANYL TELLURIDES
19
dependent on the method employed to prepare the alkali telluride as well as on the experimental conditions and solvents.
Non-activated aryl halides react only moderately with sodium telluride prepared from
the elements in inert solvents (DMF, N-methyl-2-pyrrolidone (NMP), hexamethylphosphoric acid triamide (HMPA)).1–4
Te + 2Na
solvent
Na2Te
ArX
solvent, 130 -170°C, 16 -24h
(35 - 50%)
ArTeAr
solvent = DMF, NMP, HMPA
ArX = PhI, 2 - bromonaphthalene
Better results are achieved with tellurium and sodium hydride in DMF.5
Te
NaH
DMF, 140°C
Na2Te
ArI
DMF, 130°C, 24 h
(41 - 70%)
ArTeAr
Ar = 1 - naphthyl and derivatives, 2 - fluorenyl
Diaryl tellurides (general procedure).5 A mixture of powdered Te (0.128 g, 1.0 mmol), NaH
(0.053 g, 2.2 mmol, 60% suspension in oil, washed with hexane) and dry DMF
(3 mL) is heated at 140°C for 1 h. Within 0.5 h the initial deep red colour is lost, and a
pale yellow suspension is obtained. After cooling at room temperature, the aryl iodide
(2.0 mmol) in dry DMF (3 mL) is added and the mixture heated at 130°C for 24 h. After
cooling at room temperature, the mixture is quenched with 10% aqueous NH4HSO4 (10 mL)
and extracted with ether (10 mL). The ethereal extract is washed with H2O, dried (Na2SO4)
and evaporated, giving the telluride, which is purified by column chromatography on SiO2
(eluent/hexane).
The Rongalite method (see Section 3.1.1.1b,i) can be successfully applied to the preparation of diaryl tellurides from aryl iodides.5,6 This method seems to be advantageous compared to the preceding one because of the higher yields and milder experimental
conditions.
Te
HOCH2SO2NA
NaOH / H2O
Na2Te
ArI
DMF, 60°C, 10 h
(55 - 94%)
ArTeAr
Ar = Ph and (alkyl and methoxy) derivatives, 1-naphthyl, 2 -naphthyl
and derivatives, 9 -anthryl, 9 -phenanthryl, 1-pyrenyl
Some concurrent reactions sometimes observed in the above methods (dehydrohalogenation with the tellurium/Rongalite method and formation of tellurocarbamates
RTeC(O)NMe2 with the tellurium/NaH/DMF method) that decrease the yields of the
desired tellurides can be avoided by a modified procedure, where sodium telluride is generated by heating elemental tellurium and NaH in NMP.7 The deep purple solution of the
reagent prepared under these conditions can be stored for many days (in contrast to the use
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3. PREPARATION OF THE PRINCIPAL CLASSES OF ORGANIC TELLURIUM
of DMF as the solvent) without appreciable degradation.
NaH / NMP
100 -110°C, 1 h
ArI
ArTeAr
NMP, 50 -110°C, 2 -24 h
(42-77%)
Ar = Ph and (alkyl and methoxy) derivatives, 1-naphthyl, 2-naphthyl,
1-(2-methyl)naphthyl
Te
Na2Te
Di(1-naphthyl) telluride (typical procedure).7 Finely ground Te (0.140 g, 1.1 mmol) and
NaH (2.2 mmol, 60% suspension in oil, washed with hexane) are heated in NMP (3.5 mL)
for 1 h. 1-Iodonaphthalene (0.310 g, 1.2 mmol) is added in small portions over 1.5 h to the
obtained solution of Na2Te at 100°C under argon. The resulting mixture is kept at this temperature for 19 h. During this period the colour of the solution gradually changes from
deep purple to black. The progress of the reaction is monitored by TLC. After complete
disappearance of the starting material the reaction is quenched by addition of saturated
aqueous NH4Cl (1 mL) followed by benzene (5 mL). The Te deposit is filtered off and the
filtrate is partitioned between EtOAc (30 mL) and H2O (20 mL). The organic phase is
separated and dried (Na2SO4), the solvent is evaporated and the residue chromatographed
over SiO2 (eluent/hexane), giving the telluride. The product is recrystallized from hexane/
CHCl3 (1:1) as yellow crystals (0.160 g (76%); m.p. 123–126°C).
3.1.2.2
From sodium telluride or sodium O,O-diethyl phosphorotellurolate and
arenediazonium fluoroborates
Sodium telluride and sodium O,O-diethyl phosphorotellurolate, prepared respectively by
the Te/NaBH4DMF method and by the reaction of elemental tellurium with NaH and
O,O-diethyl phosphate in ethanol, react with arenediazonium fluoroborates, giving good
yields of diaryl tellurides.8
Te
(method A) NaBH4
DMF, 100°C
(method B)(EtO)2P(O)H
NaH / EtOH, r.t.
Na2Te
[ArN2+]BF4DMF, 0-5°C, 30min
(59 - 72%)
(EtO)2P(O)TeNa
ArTeAr
[ArN2+]BF4DMF, r.t.
(64 - 94%)
A = Ph and (alkyl, methoxy, halo and acyl) derivatives
Di(p-tolyl) telluride (typical procedure).8 Method A. Elemental Te (0.65 g, 5 mmol) and
NaBH4 (0.45 g, 12 mmol) in DMF (15 mL) are heated in a Schlenk reactor at 100°C with
stirring and under N2 until disappearance of the Te powder. The solution is cooled at 0°C and
p-toluenediazonium fluoroborate (2.06 g, 10 mmol) in DMF (5 mL) is added dropwise. The
mixture is stirred at 0°C for 30 min, quenched with H2O (20 mL) and then stirred continuously for 30 min. The mixture is filtered, the filtrate extracted with ether (3⫻15 mL) and the
extracts washed with H2O (3⫻15 mL) and dried (MgSO4). The solvent is evaporated and the
residue recrystallized from MeOH, giving the telluride (1.05 g (68%); m.p. 67°C).
Method B. Elemental Te (0.64 g, 5 mmol), NaH (0.30 g, 10 mmol, 80% oil suspension,
washed with hexane) and (EtO)2P(O)H (1.41 g, 10 mmol, 97%) in anhydrous EtOH
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DIORGANYL TELLURIDES
21
(20 mL) are stirred in a Schlenk apparatus at room temperature under N2 until disappearance of the Te powder. p-Toluenediazonium fluoroborate (2.27 g, 11 mmol) in DMF
(5 mL) is added slowly and the whole stirred for 30 min. The solution is diluted with H2O,
extracted with ether (3⫻15 mL) and the extract dried (MgSO4) and evaporated. The
residue is recrystallized from MeOH, giving the telluride (1.38 g (89%); m.p. 67°C).
3.1.2.3
From potassium tellurocyanate and arenediazonium fluoroborates
Another method that uses arenediazonium fluoroborates to prepare diaryl tellurides is the
reaction with potassium tellurocyanate.9 Aryl tellurocyanides are postulated as intermediates.
2KTeCN + 2ArN2+]BF4-
DMSO, r.t.
-N2, -2KBF4
[2ArTeCN]
(41- 47%)
ArTeAr + Te(CN)2
Te + (CN)2
Ar = alkyl, methoxy, nitro, cyano, halophenyl derivatives, 2 - biphenyl
Diaryl tellurides (general procedure).9 Finely ground Te (1.6 g, 12.5 mmol) and KCN
(0.82 g, 12.5 mmol) in dry DMSO (20 mL) are heated at 100°C, for 1 h under N2. After
all the Te has dissolved, the mixture is cooled in an ice bath until most of the solvent has
solidified. The diazonium fluoroborate (12.5 mmol) is added rapidly while a brisk stream
of N2 is passed into the system. When the initial violent gas evolution has ceased, the ice
bath is removed and stirring is continued at room temperature for 3 h. The mixture is
diluted with CH2Cl2 (250 mL), filtered from the dark insoluble material (Te) and washed
several times with H2O. The solution is dried (CaCl2) and evaporated, giving an oil or a
pasty-solid, which is dissolved in CH2Cl2 and filtered through a short SiO2 column. (ln the
few cases where aryl tellurocyanides are formed as by-products, more careful chromatography is required with CH2Cl2/hexane, 1:1 as the eluent.)
The small amounts of diaryl ditellurides formed frequently as by-products can be converted into tellurides by treatment with copper powder in refluxing dioxane.10 For
Ar⫽2HO2CC6H4, the crude product is extracted with aqueous Na2CO3 and precipitated
with acid (yield 8%).
3.1.2.4
From tellurium(IV) halides and arylmagnesium halides
In this method, the electrophilic tellurium tetrachloride is employed as starting material to
introduce tellurium in organic substrates, in contrast to the preceding methods using nucleophilic tellurium species.
Tellurium tetrachloride (as well as tellurium tetrabromide and tellurium tetraiodide)
reacts with 4 mol equiv of arylmagnesium bromide, giving rise to diaryl tellurides in high
yields.11,12
TeX4 + 4ArMgBr
ether / benzene
0°C, reflux (>90%)
ArTeAr + ArAr + 4MgBrX
Ar = Ph; X = Cl, Br, I
Ar = 1-naphthyl, o -MeC6H4, p -MeC6H4; X = Br
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The intermediates in these reactions are the corresponding triaryltelluronium halides
(which react with an additional equivalent of Grignard reagent) or the unstable tetraaryltellurium derivatives.
TeX4 + 3ArMgX
[Ar3Te+]X-
TeX4 + 4ArMgX
[Ar4Te]
ArMgX
ArTeAr + ArAr
This method is an efficient modification of the early method of Lederer,13 employing tellurium dihalides (unstable compounds which disproportionate in elemental tellurium and
tellurium(IV) halides).
To make the isolation and purification of the products easier, the obtained tellurides are
converted in situ into the corresponding dichlorides, dibromides or diiodides by treating,
respectively, with sulphuryl chloride, bromine or iodine.11,12
Diphenyl telluride (typical procedure).12 To an ethereal solution of a Grignard reagent (100
mL), prepared from bromobenzene (39.3 g, 0.25 mol) and Mg (6.1 g, 0.25 mol), benzene
(100 mL) is added. The solution is cooled at 0°C and TeCl4 (13.5 g, 0.05 mol) in benzene
(200 mL) is added slowly with vigorous stirring. The reaction mixture is refluxed for 2 h,
then cooled at 0°C and quenched with saturated aqueous NH4Cl (300 mL). The organic
layer is separated, washed with H2O (3⫻), dried (Na2SO4) and evaporated in a rotatory
evaporator, giving the crude telluride. Treatment of the crude telluride with Br2 gives
diphenyltellurium dibromide (20 g (91%); m.p. 197°C).
3.1.2.5
From elemental tellurium and diarylmercury compounds
The reaction of diarylmercurials with elemental tellurium under heating, one of the oldest
methods for the preparation of diaryl tellurides,14–16 has been later employed in some specific cases.17–19
Ar2Hg + 2Te
3.1.2.6
>200°C
ArTeAr + TeHg
From diaryl ditellurides by extrusion of a tellurium atom
Diaryl ditellurides are relatively thermolabile compounds and eliminate one tellurium
atom by heating at ~300°C.20,21 In the presence of copper metal, however, the extrusion of
tellurium is achieved during reflux with toluene or dioxane.10,22–24
ArTeTeAr
~300°C
-Te
Cu
toluene, dioxane, reflux
(70 - 90%)
ArTeAr (Ar = Ph, p -MeOC6H4, p -EtOC6H4)
ArTeAr
Ar = p -MeC6H4, m -MeOC6H4, p -FC6H4, m -BrC6H4, p -NO2C6H4,
p -Me3SiC6H4, 4 - biphenyl, [2 - (2 - quinolylphenyl)]
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REFERENCES
23
Bis(2,4,6-trimethylphenyl) telluride (typical procedure).24 A solution of bis(2,4,
6-trimethylphenyl) ditelluride (4.94 g, 10 mmol) in toluene (150 mL) is refluxed in the
presence of electrolytic Cu (1.40 g, 22 mmol) for 12 h. The mixture is filtered and the
filtrate evaporated to give the pure telluride (m.p. 123–125°C).
3.1.2.7
Bis-(phenylethynyl) telluride as Te2+ equivalent
On the basis that bis-organyl tellurides undergo Te/Li exchange by treatment with an
organolithium reagent, if a thermodynamically more stable organolithium moiety is
released,25 bis-(phenylethynyl) telluride26 has been employed as starting material for the
synthesis of diaryl tellurides.27
2ArBr
t - BuLi
2ArLi
Ph CTeC Ph
ArTeAr
-2PhC CLi (75 - 100%)
THF, -78°C
Ar = Ph, p - Me2NC6H4, p - MeOC6H4, p - HOC6H4, p -MeC6H4, m - MeC6H4,
o,m-Me2C6H3, o,p,o - Me3C6H2, 2 - thienyl, p - F3CC6H4, 2 - thianapftenyl
REFERENCES
1. Sandman, J. D.; Stark, J. C.; Acampora, L. A; Gagne, P. Organometallics 1983, 2, 549.
2. Sandman, D. J.; Stark; J. C.; Rubner, M.; Acampora, L. A.; Samuelson, L. A. Mol. Cryst. Liq.
Cryst. 1983, 93, 293.
3. Acampora, L. A.; Dugger, D. L.; Emma, T.; Mohammed, J.; Rubner, M. F.; Samuelson, L.;
Sandman, D. J.; Tripathy, S. K. Polym. Electron. 1984, 36, 461.
4. Sandman, D. L.; Stark, J. C.; Acampora, C. A.; Samuelson, C. A.; Allen, G. W. Mol. Cryst. Liq.
Cryst. 1984, 107, 1.
5. Suzuki, S.; Padmanabhan, S.; Inouye, M.; Ogawa, T. Synthesis 1989, 468.
6. Suzuki, H.; Inouye, M. Chem. Lett. 1985, 389.
7. Suzuki, H.; Nakamura, T. Synthesis 1992, 549.
8. Li, J.; Lue, P.; Zhan, X. Synthesis 1992, 281.
9. Engman, L. J. Org. Chem. 1983, 48, 2920.
10. Sadekov, T. D.; Bushkov, A. Y.; Minkin, V. T. J. Gen. Chem. USSR 1973, 43, 815.
11. Rheinboldt, H.; Petragnani, N. Chem. Ber. 1956, 89, 1270.
12. McWhinnie, W. R.; Patel, M. G. J. Chem. Soc. Dalton Trans. 1972, 199.
13. (a) Lederer, K. Bericht 1915, 48, 1345, 2049. (b) Lederer, K. Bericht 1916, 49, 334, 345, 1071,
1076, 2002, 2532, 2663. (c) Lederer, K. Bericht 1917, 50, 238. (d) Lederer, K. Ber. Dtsch. Chem.
Ges. 1919, 52, 1989. (e) Lederer, K. Bericht 1920, 53, 712.
14. Kraft, F.; Lyons, R. E. Bericht 1896, 27, 1769.
15. Zeiser, F. Bericht 1895, 28, 1760.
16. Lyons, R. E.; Bush, G. H. J. Am. Chem. Soc. 1908, 30, 834.
17. Hellwinkel, D.; Farbach, G. Tetrahedron Lett. 1965, 1823.
18. Cohen, S. C.; Reddy, M. L. N.; Massey, A. G. J. Organomet. Chem. 1968, 11, 563.
19. Jones, C. W. H.; Sharma, R. D.; Naumann, D. Can. J. Chem. 1986, 64, 987.
20. Farrar, W. V. Research 1951, 4, 177.
21. Petragnani, N.; Moura Campos, M. Chem. Ber. 1961, 94, 1759.
22. Haller, W. S.; Irgolic, K. J. J. Organomet. Chem. 1972, 38, 97.
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3. PREPARATION OF THE PRINCIPAL CLASSES OF ORGANIC TELLURIUM
23. Sadekov, I. D.; Bushkov, A. Y.; Minkin, V. I. J. Gen. Chem. USSR 1977, 47, 576.
24. Akiba, M.; Lakshmikantham, M. V.; Jen, K. Y.; Cava, M. C. J. Org. Chem. 1984, 49, 4819.
25. Hiiro, T.; Kambe, N.; Ogawa, A.; Miyoshi, N.; Murai, S.; Sonoda, N. Angew. Chem. Int. Ed.
Engl. 1987, 26, 1187.
26. The synthesis of bis(phenylethynyl) telluride, isolated as the corresponding diiodide, was
described at first by Moura Campos, M.; Petragnani, N. Tetrahedron 1962, 18, 527. And later
by Dabdoub, M. J.; Comasseto, J. V.; Braga, A. L. Synth. Commun. 1988, 18, 1979. See Section
3.17.2.2.
27. Engman, L.; Stern, D. Organometallics 1993, 12, 1445.
3.1.3
Unsymmetrical tellurides
Unsymmetrical tellurides comprise a large class of organotellurium compounds characterized by two different alkyl groups, one alkyl and one aryl group, or two different aryl
groups linked to a tellurium atom. These compounds find only a minor use as reagents in
organic synthesis, but because of structural, and in some cases biological interest, their
preparation will be discussed in the following sections.
3.1.3.1
From sodium telluride and two different alkyl halides
Te
NaBH4
H2O
Na2Te
(1) RX, (2) R1X
EtOH / THF
RTeR1 (+ RTeR + R1TeR1)
(25%)
(25%)
(25%)
R = n -Bu, n - octyl, p - IC6H4(CH2)9, CH C(CH2)3, ICH CH(CH2)3
R1 = (CH2)nCO2Me
Unsymmetrical telluro-substituted fatty esters (of biological interest) are obtained in about
40% yield after chromatographic separation from the symmetrical tellurides.1
n-Octyl (7-carbomethoxy)heptyl telluride (typical procedure).1 To a suspension of elemental Te (0.127 g, 1 mmol) in H2O (3 mL) heated at 80°C is added a solution of
NaBH4 (0.100 g, 2.64 mmol) in H2O (1 mL), under red light, after careful deaeration
and argon purge. The obtained clear solution of Na2Te is cooled at room temperature
and a solution of methyl 8-bromooctanoate (0.223 g, 0.95 mmol) and 1-bromooctane
(0.202 g, 1.05 mmol) in THF/EtOH (1:1, 15 mL) is added under argon. The solution is
stirred for 1 h, poured into H2O (150 mL) and then extracted with ether (3⫻50 mL).
The ether extracts are washed with H2O (3⫻50 mL), dried (Na2SO4) and evaporated
under vacuum. The crude product is dissolved in petroleum ether (30–60°C) and purified by column chromatography on SiO2 slurried with petroleum ether (elution with
10⫻25 mL aliquots of petroleum ether followed by 10⫻25 mL aliquots of benzene,
monitoring the fractions by TLC). By combination of aliquots 13–16 the telluride is
obtained as an oil (0.155 g (39%)).
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DIORGANYL TELLURIDES
25
Aryl alkyl tellurides are prepared in medium yields by sequential arylation/alkylation of
Na2Te generated by the described Te/NaH/NMP system (see Section 3.1.2.1).2
Te
NaH
NMP, 100 - 110°C, 1 h
Na2Te
ArI (0.5 equiv)
NMP, 120°C, 2 - 4 h
[ArTe-]
Ar = o - MeC6H4, 1-naphthyl; R = n - hepthyl
Ar = 2- naphthyl; R = Me
RX
NMP, 50°C, 2 h
(52 - 67%)
ArTeAr
Methyl 2-naphthyl telluride (typical procedure).2 2-Iodonaphthalene (0.150 g, 0.59 mmol)
is added dropwise to a stirred solution of Na2Te (1.3 mmol) in NMP (4 mL) and the mixture is heated at 120°C for 5 h. An excess of MeI (0.40 mL, 4.3 mmol) is then added and
the resulting mixture is stirred at 50°C for 2 h. Usual work-up gives the telluride as pale
yellow crystals (0.110 g (67%); m.p. 59–60°C).
3.1.3.2
From organyl tellurolates and alkylating agents
(a) From organyl tellurolates generated by tellurium insertion in organomagnesium or
organolithium reagents
The magnesium aryl tellurolates described earlier 3 have seldom been employed for the
preparation of unsymmetrical tellurides.4–6
Te + ArMgBr
ArTeMgBr
RX
ArTeR
Ar = Ph; R = Et, H2C-C CH
Ar = o-MeS-, o-Me2N, o-ClC6H4; R = Me (68-92%)
Elemental tellurium also inserts easily into a C(sp2)–Mg bond of a vinyl or styryl
Grignard reagent (see Section 3.16.1.4), but is unaffected by alkylmagnesium halides.7
In contrast, tellurium insertion in alkyl- or aryllithium compounds followed by alkylation is a useful method for the synthesis of unsymmetrical tellurides. (For a tabulation of
unsymmetrical tellurides prepared by alkylation of organyl tellurolates, see ref. 8.)
Te + RLi
Te + ArLi
1
RTeLi R X
ArTeLi RX
RTeR1
ArTeR
Methyl (3-hydroxy)propyl telluride (typical procedure).9 MeTeLi. A suspension of Te powder (12.8 g, 0.1 mol) in THF (100 mL) is frozen in a liquid N2 bath, and then MeLi (66.7
mL of a 1.5 M solution in ether, 0.1 mol) is injected into the flask. The mixture is allowed
to thaw and is stirred magnetically for a further 30 min at room temperature. The resulting
yellow-orange solution is stored under N2 and used within 2 h.
MeTe(CH2)3OH. 3-Bromopropan-1-ol (6.95 g, 50 mmol) is injected into a frozen (by liquid
N2) solution of MeTeLi (50 mmol). The mixture is allowed to thaw and is stirred magnetically at room temperature for about 1 h. Aqueous NaCl (100 mL) is then added and the
aqueous layer extracted several times with ether. The combined organic phases are dried
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3. PREPARATION OF THE PRINCIPAL CLASSES OF ORGANIC TELLURIUM
(MgSO4) for 16 h, and evaporated. The residue is chromatographed on an SiO2 column (elution with petroleum ether 40–60°C), giving the telluride (8.3 g (83%)) in acceptable purity.
Methyl phenyl telluride (typical procedure).10 To a well-stirred suspension of Te powder
(3.0 g, 24 mmol) in anhydrous THF (36 mL) under argon is added dropwise an equimolar
amount of PhLi (1.5–2.0 M in ether). The mixture is then stirred for 2 h at room temperature, and for 1 h under reflux, and then MeI (3.4 g, 24 mmol) is added. After refluxing for
0.5 h the mixture is poured into three volumes of H2O, the aqueous layer is extracted with
CH2Cl2, and the combined organic phases are washed with H2O, dried (Na2SO4) and evaporated. The oily brown residue is distilled under vacuum, giving the telluride (2.1 g (43%);
b.p. 57–58°C/0.7 torr).
(b) From organyl tellurolates generated by the cleavage of ditellurides with alkali metals
or reducing agents
The reductive fission of diaryl ditellurides with sodium in liquid ammonia reported earlier11 has seldom been employed.12,13 More recently, aprotic solvents have been substituted
for ammonia.14–16
A practical and successful method employs lithium in THF.17
ArTeTeAr
Li
THF
ArTeLi
RX
ArTeR
Ar = Ph; R = Me, Et, n -Pr, n -Bu, n -C14H29 (62-84%)
R = i -prop (46%)
Alkyl phenyl tellurides (general procedure).17 Li metal (1.4 g, 0.2 mol) in small pieces is
added under N2 to a solution of diphenyl ditelluride (4.1 g, 10 mmol) in dry THF (100 mL).
The mixture is stirred at room temperature for 6 h, unreacted lithium is removed using a
spatula and the alkyl halide (20 mmol) neat or in THF is added dropwise to the stirred
yellowish-brown solution. The solution is stirred at room temperature for 30 min, and under
reflux for an additional 30 min. The solvent is evaporated, and H2O (10 mL) and ether
(25 mL) are added to the residue, mixing thoroughly. The ethereal phase is separated and
evaporated. The residue is fractionally distilled under vacuum (yields 62–79%).
Actually, the method of choice for the preparation of organyl tellurolate anions is the
reduction of diorganyl ditellurides with reducing agents.
NaBH4 is the more widely used reagent owing to the mild experimental conditions. The
choice of solvent, or solvent mixture, and of neutral or basic media is governed by the further use of the tellurolate solution. Typical media are benzene/ethanol/aqueous NaOH,18
MeOH or EtOH.19–21
ArTeTeAr (RTeTeR)
NaBH4
EtOH (MeOH)
ArTeNa (RTeNa)
R 1X
ArTeR1 (RTeR1)
Medium-to-high yields of the expected tellurides are obtained from diaryl or dialkyl
ditellurides and n- and s-alkyl halides (and steroidal tosylates).
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DIORGANYL TELLURIDES
27
Reactions with epoxides are also successful, giving the corresponding hydroxy tellurides.19
ArTeNa +
R
O
R
R
OH
ArTe
R
Phenyl dodecyl telluride (typical procedure).19 To a solution of diphenyl ditelluride
(1.21 g, 2.96 mmol) in absolute EtOH (100 mL) is slowly added powdered NaBH4
(0.23 g, 6.08 mmol) under N2 at room temperature. At the end of the addition the
red colour is discharged and 1-bromododecane (1.5 g, 6.02 mmol) is added by a
syringe. The mixture is refluxed for 3.5 h (during this period the progress of the reaction is monitored by TLC; the plates are developed in the dark) and then evaporated.
The residue is purified by chromatography on SiO2 (eluting with CCl4), giving the telluride (1.73 g (76%)).
Diaryl ditellurides, like diaryl disulphides and diselenides,22 undergo disproportionation
into arene tellurolates and tellurinates by alkaline treatment.
3ArTe- + ArTeO2- + 2H2O
2ArTeTeAr + 4OH-
The tellurolate anion formed can be alkylated in situ, giving alkyl aryl tellurides, if the
above reaction is effected in the presence of a phase transfer catalyst.23 Otherwise, performing the reaction in the presence of the reducing agent TUDO a telluride yield near
to quantitative is generated, owing to the reduction of the aryl tellurinate anion to aryl
tellurolate.24
2ArTeTeAr + 4OH-
PTC
3ArTe- + ArTeO2- + 2H2O
TUDO
ArTe- + RX
ArTeR
(81-96%)
Ar = Ph, 2-naphthyl, p -MeOC6H4, m-F3CC6H4
R = n- and s-alkyl, benzyl
Alkyl aryl tellurides (general procedure).24 To a solution of diaryl ditelluride (1.0 mmol)
in THF (7.5 mL) are added TUDO (0.108 g, 1.0 mmol), 2HT (0.030 g) and the alkyl halide
(2.0 mmol). Then, 50% NaOH (7.5 mL) is added and the mixture is stirred vigorously for
several hours at room temperature. The phases are separated, and the organic phase is
extracted with EtOAc (3⫻20 mL). The combined organic phases are washed with H2O,
dried (MgSO4) and evaporated. The residue is purified by column chromatography on SiO2
(eluting with EtOAc).
Aryl ditellurides are cleaved by samarium diiodide (SmI2) to generate the new nucleophilic species diiodosamarium aryl tellurolate which reacts smoothly with alkyl and acyl
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3. PREPARATION OF THE PRINCIPAL CLASSES OF ORGANIC TELLURIUM
halides, and even with aryl halides to afford the corresponding tellurides and telluroesters.25–27
ArTeTeAr + 2SmI2
THF / HMPA
r.t., 0.5 h, 1 h
2 "ArTeSmI2"
ArTeR
RCOCl
r.t., 2 h
CN
X
C C
H Y
THF, r.t., 3h
ArTe
RX
r.t., THF, 3 h
ArTeCOR
(77, 72%)
CN
C C
H Y
(64-85%)
Ar = Ph
X = Br, I
R = Me, Et, prop, n -Bu
i -propyl, PhCH2
Ar = Ph, p -MeC6H4
R = Ph
Ar = Ph, p -MeC6H4
X = Cl, Br
Y = CN, CO2Et
Reaction of diphenyl ditelluride with organic halides mediated by SmI2.25 Samarium
powder (0.20 g, 1.3 mmol) was placed in a well-dried, two-neck, round-bottom flask containing a magnetic stirrer bar. The flask was flushed with nitrogen several times.
Methylene diiodide (0.32 g, 1.2 mmol) in THF (7 mL) was added through a rubber septum by a syringe. The mixture was stirred at room temperature until the solution became
deep green and homogeneous (0.5–1 h). HMPA (0.7 mL) was then added and the solution became deep purple; the THF-HMPA solution of SmI2 was ready for subsequent use.
To the THF-HMPA (7–0.7 mL) solution of SmI2 (1.2 mmol), prepared as described
above, was added a mixture of ditelluride (0.21 g, 0.5 mmol) and organic halide (1 mmol)
in THF (7 mL) at room temperature, and the solution was stirred for 5 h, during which time
its colour changed into brownish-yellow. The reaction solution was poured into diluted
HCl, and the mixture was extracted with ether (2⫻15 mL). The ethereal solution was
treated with aqueous Na2S2O3, washed with brine, and dried (MgSO4). Evaporation of the
solvent left a yellow oil that was subjected to preparative TLC on silica gel (petroleum
ether as eluent), giving the phenylalkyl tellurides.
Diisobutylaluminium benzenetellurolate, generated in situ from diphenyl ditelluride and
diisobutylaluminium (DIBAL), reacts with acetals, alkyl sulphonates and oxiranes, giving
the expected tellurides in high yields.28
(i-Bu)2AlTePh
RCH(OMe)2
CH2Cl2
re
OMe
TePh
R = H, C11H23
(42-80%)
RCH
r.t.
flu
x
C11H23CH
TePh
TePh
(50%)
C6H13OMs(OTs)
OMs
( )11
same condition
same condition
C6H13TePh
(72%)
TePh
( )11
(46%)
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DIORGANYL TELLURIDES
29
OH
O
same condition
RCHCH2TePh
(70-88%)
R
R = Me, Et, C12H25
O
( )n
OH
same condition
( )n TePh
n = 4, 10
(c)
(80%)
From organyl telluroesters generated by the reduction of organyltellurium
trichlorides with NaBH4
The reaction of organyltellurium trichlorides with NaBH4 followed by the in situ treatment
of the generated tellurolate with alkyl halides is a useful method to prepare several types
of unsymmetrical telluride.29
NaBH4
RX
ArTeR
ArTeNa
THF/H2O
THF/N2 (88-95%)
0°C
Ar = Ph, p -MeOC6H4, p -C6H5OC6H4
RX = MeI, EtBr, Me(CH2)2CH(Me)Br
ArTeCl3
Transformation of aryltellurium trichlorides into alkyl aryl tellurides (typical procedure).29 To a solution of the aryltellurium trichloride (5 mmol) and the appropriate alkyl
halide (7.5 mmol) in THF (60 mL) under a nitrogen atmosphere, was slowly added a solution of NaBH4 (0.93 g, 25 mmol) in water (30 mL) at 0°C. The colour changed from
yellow to red when the addition of NaBH4 started and to yellow again after the addition
was completed. After the addition, the mixture was stirred for 20 min at room temperature
and then treated with saturated aqueous solution of NH4Cl (100 mL) and extracted with
ethyl acetate (3⫻20 mL). The extracts were washed with brine (3⫻20 mL) dried with
MgSO4 and the solvents were evaporated. The residue was purified by column chromatography on silica gel, eluting with hexane, to give the aryl–alkyl tellurides.
Vinylic30 and cyclic organyltellurium trichlorides31 undergo similar reactions.
R
Cl
R1
1) NaBH4
TeCl3
THF/ H2O
2) EtBr / N2
Cl
R = Ph; R1 = Ph, Me
R2
R1 ( )n
R
O
R1
R
TeEt
(78, 75%)
1) NaBH4
TeCl3 THF/ H O
2
2) n-BuBr
n=1
R, R1, R2 = H
R = i -prop; R1, R2 = Me
n=2
R, R1, R2 = H
R2
R1 ( )n
R
TeBu-n
O
(90-95%)
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3. PREPARATION OF THE PRINCIPAL CLASSES OF ORGANIC TELLURIUM
By addition of aryl tellurolates to electrophilic alkenes
Aryl tellurolates add to alkenes bearing electron-withdrawing groups in a typical 1,4-Michael
addition, giving -telluro-substituted derivative.32
R
Y
PhTeNa / EtOH
(PhTe)2 / NaBH4
(31-71%)
R
PhTe
Y
R = H, Me; Y = CO2Et, CN
THF
Te + RLi
r.t., N2
EtOH
[RTeLi]
r.t.
[RTeH]
R1
R2
EWG
RTe
R1 2
R
R = Bu, s- Bu
EWG = CN, CHO, COR, CO2R
R1, R2 = H
R1 = H; R2 = Me, cyclohexenone, 4,4 - dimethyl cyclohexenone
EWG
(98%)
3.1.3.4 From organyl tellurolates and arylating agents
The arylation of organyl tellurolates, restricted first to aryl halides activated by electronwithdrawing groups,24 or requiring special conditions such as heating in HMPA in the
presence of CuI,33 or photostimulation in liquid ammonia,12,13 has later been achieved successfully with non-activated aryl halides under normal conditions.6
PhTeTePh
1) NaBH4 / HMPA, 70 - 80°C
2) CuI, 3) ArI (80 - 90%)
Ar = nitroaryl
PhTeTePh
RLi + Te
Na/ NH3
ArX
UV
PhTeNa
RTeLi
ArX
PhTeAr
[ref. 33]
PhTeAr
(ref. 12,13)
RTeAr (R = Me, Ph)
(ref. 6)
Methyl o-methoxyphenyl telluride (typical procedure).6 To a frozen solution of MeTeLi (50
mmol) is added o-bromoanisole (9.3 g, 50 mmol). The mixture is allowed to warm at room
temperature, stirred for 1.5 h and then quenched with deoxygenated H2O (100 mL). The
organic product is extracted with ether (3⫻50 mL), the organic extracts dried (MgSO4) for
16 h and evaporated, and the residue is distilled under vacuum, giving the telluride as a
pale yellow oil (9.3 g (74%)).
Arenediazonium salts34,35 as well as arenesulphonylazo compounds36 have also found a
use as arylating agents for arene tellurolates.
ArTeTeAr
NaBH4
EtOH/THF/NaOH aq.
PhTeLi + ArN = NSO2C6H4CH3
ArTeNa
[Ar1N2+]X-
18-crown-6
MeCN, r.t.
PhTeAr
ArTeAr1
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31
Reaction of diarylditellurides with arenediazonium salts (typical procedure). p-Methoxy
phenyl p-tolyl telluride.35 With heating and stirring in an atmosphere of nitrogen, sodium
tetrahydroborate was added in small portions to a solution of 9.4 g of bis(p-methoxyphenyl)
ditelluride in a mixture of 50 mL of ethanol and 15 mL of benzene until the solution was
decolourized completely (1.5 g was required). Then 8.24 g of p-toluenediazonium fluoroborate was added rapidly and the mixture was stirred for 1 h and poured into dilute HCl.
The oil formed was extracted with ether, and the extract was washed with water and dried
over CaCl2. Ether was evaporated, and the residue was dissolved in benzene and chromatographed on alumina (eluent hexane). After the evaporation of hexane, 4.8 g (36%) of
the telluride was isolated, m.p. 64–64.5°C (hexane).
Trimethylsylilmethyl telluride generated in situ from methyllithium and trimethylchlorosilane can be used instead of the tellurolate in the latter reaction.36
MeTeLi + Me3SiCl
3.1.3.5
MeTeSiMe3
ArN = NSO2C6H4CH3
MeTeAr
From diorganyl ditellurides or arenetellurenyl halides and organometallic
reagents
A different approach to unsymmetrical diorganyl tellurides, in which an electrophilic tellurium species is used, involves the nucleophilic attack of organomagnesium or organolithium reagents to diorganyl ditellurides.
RTeTeR + R1Met
R
aryl
aryl, alkyl
alkyl
RTeR1 + RTeMet
R1
Met
aryl
alkyl
alkyl
MgX, Li
MgX, Li
Li
(ref. 37, 39)
(ref. 39, 40)
(ref. 38, 6)
Only half of the tellurium of the starting ditelluride is converted into telluride. The other
half, converted into tellurolate, can be oxidatively recovered as the starting ditelluride.
If the diaryl ditelluride is previously converted in situ into the corresponding tellurenyl
halide, both the electrophilic tellurium moieties are used.41 (The stable crystalline 2-naphthyltellurenyl iodide42 (see Section 3.7) reacts similarly.) The reaction is of general application, giving high yields of the expected tellurides with aromatic, aliphatic, cycloaliphatic,
vinylic43 and acetylenic Grignard reagents,44 under mild conditions.
ArTeTeAr
X2
THF / benzene
[ArTeX]
RMgX
(>90%)
ArTeR
Ar = Ph, p -Me, p -MeO, p -EtOC6H4
R = Ph, n-Bu, cyclohexyl, PhC C ; X = Br, I
Unsymmetrical diorganyl tellurides (general procedure).41 A solution of the ditelluride
(2 mmol) in THF (30 mL) is treated dropwise at 0°C under N2 with Br2 (0.32 g, 3 mmol)
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in benzene (4 mL). The Grignard reagent is then added dropwise by means of a syringe.
Gradual disappearance of the red colour of the solution is observed. Finally, the solution
becomes almost colourless after the addition of a 10% excess of the Grignard reagent.
After stirring for 30 min at room temperature the solution is diluted with petroleum ether
30–60 C (30 mL) and treated successively with aqueous NH4Cl and brine. The organic
layer is dried (MgSO4) and evaporated, giving the telluride.
3.1.3.6
Additional methods
(a) From dialkyl ditellurides and arenediazonium fIuoroborates45
RTeTeR
[ArN2+]BF4-
ArTeR
CHCl3(CH2Cl2), KOAc,
18-crown-6
(25 - 48%)
R = Et
Ar = 2-halC6H4, 2-MeC6H4, 3-MeC6H4, 4-MeC6H4,
2-AcC6H4, 2-CO2HC6H4
(b) From diaryl ditellurides and dialkylmercury reagents46,47
ArTeTeAr + R2Hg
dioxane / reflux
-Hg (70 -80%)
2 ArTeR
Ar = Ph
R = n -C4H9, i -C4H9, Bz
(c) From phenyl tellurocyanate and alcohols48
PhTeTePh
1) NaBH4
2) BrCN
PhTeCN
ROH
Bu3P / CH2Cl2
PhTeR
(41-78%)
R = n -C8H17, n -C11H23, n -C12H25, n -C14H29, n -C16H33,
Ph(CH2)2, Ph(CH2)3, n -C12H25CHCH3
(d) From diphenyl ditellurides and trialkyl boranes49
PhTeTePh
R3B
O2 / THF
RTePh
(64 -95%)
Selected examples:
R = n -C6H13, n -C16H33, c-hex, Br(CH2)5,
PhCH2OCO(CH2)4
R3B = n -C6H13B(c-hex)2
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REFERENCES
33
(e) From trimethylsylilphenyl tellurium and organyl halides50
Me3SiTePh + RX
MeCN
RTePh + Me3SiX
(60-100%)
X = Br
R = sec - C10H21, PhCH2, o -ClC6H4CH2, m -ClC6H4CH2, Ph
allyl, cinnamyl, c - hex, t - But (36%),
(48%),
N
CH2
CH2 ,
N
N
N
( f ) From arylethynyl tellurides and aryllithium
The protocol shown in Section 3.1.2.7 is also useful to prepare unsymmetrical diaryl
tellurides.51
ArTe-C
Ph + Ar1Li
THF
-78°C
ArTeAr1 + PhC CLi
(44-85%)
Ar = p -Me2NC6H4, p -MeOC6H4
Ar1 = Ph, p -MeOC6H4, p -MeC6H4, p -FC6H4, p -F3CC6H4
(g) From aryltellurium tribromides and arylboronic acids52
ArB(OH)2 + Ar1TeBr3
MeNO2
reflux, 30min
Ar Te Ar1
Br Br
NaHSO3
ArTeAr1
(46 - 54%)
Ar = o -NO2C6H4, m -NO2C6H4
Ar1 = m, m -Me2C6H3
(h) From diaryl ditellurides and ethyldiazoacetate53
PhTeTePh
N2CHCO2Et
PhTeCH2CO2Et
CuSO4, benzene
(70%)
reflux
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
Goodman, M. M.; Knapp Jr., F. F. Organometallics 1983, 2, 1106.
Suzuki, H.; Nakamura, T. Synthesis 1992, 549.
Giua, M.; Cherchi, F. Gazz. Chim. It. 1920, 50, 362.
Bowden, K.; Braude, A. E. J. Chem. Soc. 1952, 1076.
Pourcelot, G.; Lequan, M.; Simmonin, M. P.; Cadiot, P. Bull. Soc. Chim. Fr. 1962, 1278.
Kemmitt, T.; Levanson, W. Organometallics 1989, 8, 1303.
Haller, W. S.; Irgolic, K. J. J. Organomet. Chem. 1972, 38, 97.
Irgolic, K. J. in Houben-Weyl-Methods of Organic Chemistry. 4th edn, Vol. E12b, p. 389. Georg
Thieme, Stuttgart, 1990.
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3. PREPARATION OF THE PRINCIPAL CLASSES OF ORGANIC TELLURIUM
9. Hope, E. G.; Kemmitt, T.; Levanson, W. Organometallics 1988, 7, 78.
10. Seebach, D.; Beck, A. K. Chem. Ber. 1975, 108, 314.
11. Lederer, K. Ber. Dtsch. Chem. Ges. 1915, 48, 1345; see also Liesk, J.; Schultz, P.; Klar, G. Z.
Anorg. AlIg. Chem. 1977, 435, 98.
12. Pierini, A. B.; Rossi, R. A. J. Organomet. Chem. 1979, 168, 163.
13. Pierini, A. B.; Rossi, R. A. J. Org. Chem. 1979, 44, 4667.
14. Uemura, S.; Fukuzawa, S. I.; Yamauchi, T.; Hattori, K.; Mizutaki, S.; Tamaki, K. J. Chem. Soc.
Chem. Commun. 1984, 426.
15. Engman, L. Organometallics 1986, 5, 427.
16. Ohe, K.; Takahashi, H.; Uemura, S.; Sugita, N. J. Organomet. Chem. 1987, 326, 35.
17. Irgolic, K. J.; Busse, P. J.; Grigsby, R. A.; Smith, M. R. J. Organomet. Chem. 1975, 88, 175.
18. Piette, J. L.; Renson, M. Bull. Soc. Chim. Belg. 1970, 79, 353.
19. Clive, D. L.; Chittattu, G. J.; Farina, V.; Kiel, W. A.; Menchen, S. M.; Russel, C. G.; Sing, A.;
Wong, C. K.; Curtis, N. J. J. Am. Chem. Soc. 1980, 102, 4438.
20. Knapp, F. F.; Ambrose, K. R.; Callahan, A. P. J. Med. Chem. 1981, 24, 794.
21. Uemura, S.; Fukuzawa, S. J. Am. Chem. Soc. 1983, 105, 2748.
22. Rheinboldt, H. in Houben-Weyl-Methoden der Organischen Chemie (ed. E. Muller). 4th edn,
Vol. IX, p. 1102. Georg Thieme, Stuttgart, 1955.
23. Comasseto, J. V.; Ferreira, J. T. B.; Fontanellas, J. A. J. Organomet. Chem. 1984, 277, 261.
24. Comasseto, J. V.; Lang, E. S.; Ferreira, J. T. B.; Simonelli F.; Correia, V. R. J. Organomet. Chem.
1987, 334, 329.
25. Fukuzawa, S. I.; Niimoto, Y.; Fujinami, T.; Sakai, S. Heteroatom. Chem. 1990, 1, 491.
26. Zhang, Y.; Yu, Y.; Lin, R. Synth. Commun. 1993, 23, 189.
27. Bao, W.; Zhang, Y. Synth. Commun. 1995, 25, 1913.
28. Sasaki, K.; Mori, T.; Doi, Y.; Kawachi, A.; Aso, Y.; Otsubo, T.; Ogura, F. Chem. Lett. 1991, 415.
29. Chieffi, A.; Menezes, P. H.; Comasseto, J. V. Organometallics 1997, 16, 809.
30. See Section 3.16.2.1.
31. See Section 4.5.1.1.
32. (a) Ohe, K.; Takahashi, H.; Uemura, S.; Sugita, M. Nippon Kagaku Kaishi 1987, 1469. (b) Zinn,
F. K.; Righi, V. E.; Luque, S. C.; Formiga, H. B.; Comasseto, J. V. Tetrahedron Lett. 2002, 43,
1625.
33. Suzuki, H.; Abe, H.; Ohmasa, N.; Osuka, A. Chem. Lett. 1981, 1115.
34. Piette, L.; Thibaut, P.; Renson, M. Tetrahedron 1978, 34, 655.
35. Sadekov, J. D.; Ladatko, A. A.; Minkin, U. I. J. Gen. Chem. USSR 1977, 47, 2194.
36. Evers, M. J.; Christiaens, L. E.; Renson, M. J. J. Org. Chem. 1986, 51, 5196.
37. Petragnani, N. Chem. Ber. 1963, 86, 247.
38. Herberhold, M.; Leitner, P. J. Organomet. Chem. 1987, 336, 153.
39. O⬘Brien, D. H.; Dereu, N., Huang, C. K.; Irgolic, K. J.; Knapp, F. F. Organometallics 1983, 2,
305.
40. Dereu, N.; Piette, I. L. Bull. Soc. Chem. Fr. 1979, 623.
41. Petragnani, N.; Torres, L.; Wynne. K. J. J. Organomet. Chem. 1975, 92, 185.
42. Vicentini, G. ; Giesbrecht E.; Pitombo, L. R. M. Chem. Ber. 1959, 92,40.
43. Dadboub, M.; Dabdoub, V. M.; Comasseto, J. V.; Petragnani, N. J. Organomet. Chem. 1986,
308, 211.
44. Moura Campos, M.; Petragnani, N. Tetrahedron 1982, 18, 527.
45. Luxen, A.; Christiaens, L. Tetrahedron Lett. 1982, 3905.
46. Okamoto, Y.; Yano, T. J. Organomet. Chem. 1971, 29, 99.
47. Vychkova, T. I.; Kalabin, G. A.; Kushnarev, D. F. J. Org. Chem. Russia 1982, 17, 1179.
48. Ogura, F.; Yamaguchi, H.; Otsubo, T.; Chikamatsu, K. Synth. Commun. 1982, 12, 131.
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REFERENCES
49.
50.
51.
52.
53.
35
Abe, T., Aso, Y.; Otsubo, T.; Ogura, F. Chem. Lett. 1990, 1671.
Yamago, S.; Lida, K.; Yoshida, J. I. Tetrahedron Lett. 2001, 42, 5061.
Engman, L.; Stern, D. Organometallics 1993, 12, 1445.
Clark, A. R.; Nair, R.; Fronczek, F. R.; Junk, T. Tetrahedron Lett. 2002, 43, 1387.
Dabdoub, M.; Guerrero, P. G.; Silveira, C. C. J. Organomet. Chem. 1993, 460, 31.
3.1.4 Diorganyl tellurides by reduction of diorganyltellurium dihalides
Diorganyltellurium dihalides are often the primary products in the synthesis of organic
derivatives of tellurium and are therefore immediate precursors of the corresponding
tellurides.
The most employed reducing agents in the “old” tellurium chemistry were alkali sulphites or hydrogen sulphites, methylmagnesium iodide and sodium sulphide hydrate. The
last reagent is still used, together with the more recently introduced sodium borohydride,
TUDO, hydrazine, samarium diiodide and sodium ascorbate.1
red
RTeR
RTeR
X X
Often the sequence
R2Te
X2
R2TeX2
red
R2Te
is employed for isolation and purification purposes, since the dihalides are generally
solid, easily recrystallizable compounds, and the two steps cause only a little loss in the
telluride yield.
Reduction of diorganyltellurium dihalides
With sodium sulphide hydrate (general procedure).2 The diorganyltellurium dihalide is
mixed with a 15 times molar excess of Na2S·9H2O and the mixture heated at 95–100°C for
10 min or more, until all the solid has melted. Sufficient H2O is added to dissolve the sulphide and then the mixture is filtered if the obtained telluride is a solid, or extracted with
a solvent (ether or petroleum ether) if the telluride is a liquid. The products are purified by
crystallization or distillation. Yields are high or quantitative (except for diphenyl telluride
or di-p-tolyl telluride).
With sodium borohydride – tetrahydrotellurophene (typical procedure.3 NaBH4 is added to
a boiling methanolic solution of diiodotetrahydrotellurophene until the orange colour disappears. The solution is filtered and the filtrate is poured into H2O (1 L). Extraction with
ether, followed by drying (CaCl2) and evaporation, gives the product as a yellow oil with
a persistent odour (b.p. 165–167°C/760 mmHg; no yield was given).
With TUDO (general procedure).4 A mixture of diorganyltellurium dihalide (2 mmol) and
2 N NaOH (10 mL) is stirred at room temperature for 15 min. TUDO (0.432 g, 4 mmol)
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and petroleum ether (30–60°C, 10 mL) are then added and the two-phase system is stirred
at room temperature until the mixture turns clear. The phases are separated and the aqueous
phase is extracted with ether (3⫻). The combined organic phases are dried (MgSO4) and the
solvent is evaporated. The residue is placed on an SiO2 column and eluted with petroleum
ether giving the telluride (dibutyl, didodecyl, butyl phenyl, and di-4-methoxyphenyl telluride; yields 77–90%).
With hydrazine – di-p-anisyl telluride (typical procedure).5 p-Anisyltellurium dichloride
(8.3 g, 0.02 mol) suspended in EtOH/H2O (150:15) is heated under reflux, and hydrazine
(3.2 g, 0.1 mol) is added dropwise (vigorous evolution of N2). When further addition of
hydrazine no longer causes evolution of N2, the mixture is poured into H2O (700 mL), and
extracted with ether (2⫻300 mL). The extracts are washed with H2O, dried and evaporated, giving the telluride. The product is recrystallized from MeOH (at ⫺25°C) (5.2 g
(77%); m.p. 57°C).
3.1.5
Additional methods
Sodium ascorbate6 and samarium diiodide7 have also been used as reducing agents.
Reduction of diaryltellurium dichlorides with sodium ascorbate (typical procedure).6 Bis
(p-methoxyphenyl)tellurium dichloride (0.20 g, 0.48 mmol) dissolved in acetone (10 mL)
was added to a stirred solution of sodium ascorbate (0.20 g, 1.0 mmol) in water/methanol
(2⫹8 mL). After 24 h, water (50 mL) and CH2Cl2 (50 mL) were added and the two phases
separated. The organic phase was dried (CaCl2) and the solvent evaporated in vacuo. Flash
chromatography yielded 0.14 g (84%) of bis(p-methoxyphenyl) telluride.
Reduction of diaryltellurium dichlorides with samarium diiodide (typical procedure).7
Diaryl tellurium dichloride (1 mmol) was added to the deep blue solution of SmI2 (2.2
mmol) in THF (22 mL) at room temperature under nitrogen with stirring. The deep blue
colour of the solution disappeared immediately and became yellow. The resulting solution
was stirred at room temperature under nitrogen for 30 min. To the solution was added
dilute hydrochloric acid, and the mixture was extracted with ether. The ethereal solution
was washed with brine and dried over MgSO4. The solvent was evaporated in vacuo, and
the residue was purified by preparative TLC on silica gel (petroleum ether–methylene
dichloride as eluent).
REFERENCES
1. For an extensive coverage on the reduction of diorganyltellurium dichloride see: Rheinboldt, H.
in Houben-Weyl-Methoden der Organishen Chemie (ed. E. Muller). 4th edn, Vol. IX, p. 1068.
Georg Thieme, Stuttgart, 1955. Irgolic, K. J. in Houben-Weyl-Methods of Organic Chemistry.
4th edn, Vol. El2b, p. 426. Georg Thieme, Stuttgart, 1990.
2. Reichel L.; Kirschbaum, E. Chem. Ber. 1943, 76, 1105.
3. AI-Rubaie, A. Z.; Alshirayda, H. A. Y. J. Organomet. Chem. 1985, 287, 321.
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4.
5.
6.
7.
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DIORGANYL DITELLURIDES
37
Lang, E. S.; Comasseto, J. V. Synth. Commun. 1988, 18, 301.
Bergman, J. Tetrahedron 1972, 28, 3323.
Engman, L.; Persson, J. Synth. Commun. 1993, 23, 445.
Jia, X.; Jin, P.; Zhang, Y.; Zhou, X. Synth. Commun. 1995, 25, 253.
3.2
DIORGANYL DITELLURIDES
Three main routes have been well established for the preparation of diorganyl ditellurides:
(1)
The reaction of sodium ditelluride with alkylating or arylating agents.
NaTeTeNa + RX
(2)
The oxidation of tellurols or tellurolate anions.
RTeH (RTe-)
(3)
RTeTeR
ox.
RTeTeR
The reduction of organyltellurium trichlorides.
RTeCl3
red.
RTeTeR
R = alkyl, aryl
3.2.1
3.2.1.1
From sodium ditelluride
From sodium ditelluride and alkylating agents
This is the most direct route to diorganyl ditellurides and therefore parallels the route leading to diorganyl tellurides, substituting sodium telluride for sodium ditelluride. Sodium
ditelluride is prepared employing, with the appropriate ratio of the elements, methods analogous to those described for sodium telluride.
(a) Liquid ammonia method
Dimethyl ditelluride (typical procedure).1 Clean Na metal (3.2 g, 0.14 mol) is added to 100
mL of liquid NH3 at ⫺78°C. After stirring for 1 h, high-purity powdered Te (18.2 g, 0.14
mol) is added in 0.5 g portions. Methyl iodide (24 g, 0.17 mol) is then added dropwise for
20 min, with stirring, to the dark green solution. The NH3 is evaporated, H2O is added to
the residue and the mixture extracted with ether (4⫻50 mL). The combined deep red
extracts are dried overnight (CaCl2), and evaporated under vacuum. The residue is then distilled (7.6 g (38%); b.p. 97°C/9 torr).
Diethyl ditelluride and dibenzyl ditelluride are prepared similarly2 in yields of 71% and
82%, respectively.
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(b) Sodium naphthalene method
Dialkyl ditellurides (general procedure).3 A mixture of powdered Te (3.58 g, 28 mmol),
Na chips (0.65 g, 28 mmol) and naphthalene (0.36 g, 2.8 mmol) in anhydrous THF
(25 mL) is refluxed under N2 and stirred for 1 h. During this time all the sodium is consumed
and the mixture turns a light brown colour. The solution is stirred for an additional 3 h to
ensure the complete reduction of Te, the temperature is then lowered to 10°C and the alkyl
halide (28 mmol) is added dropwise for 30 min with stirring. After an additional hour of
stirring at room temperature, the reaction mixture is filtered, the solvent evaporated and the
residue distilled under vacuum, giving the pure ditelluride (R⫽Et (85%), n-Pr (90%),
n-Bu (90%), MeOCH2CH2 (60%)).
(c) Sodium hydride/DMF method
Bis(4-carbomethoxy)butyl ditelluride (typical procedure).4 Powdered Te (1.27 g, 10
mmol), NaH (0.44 g, 11 mmol) and dry DMF (50 mL) are stirred at 70°C under argon for
3 h. The purple Na2Te2 solution is cooled at room temperature, and methyl 5-bromovalerate (2.15 g, 11 mmol) in dry argon-purged DMF (10 mL) is added. The mixture is stirred
at room temperature for 1 h, cooled and poured into H2O (100 mL) and extracted several
times with ether. The combined extracts are washed thoroughly with H2O, dried (Na2SO4)
and evaporated under vacuum, giving a dark orange oil. The crude ditelluride is chromatographed on SiO2 (basic, 125 g eluting with CHCl3). Dark orange oil (1.38 g (53%));
single component on TLC (Rf ⫽0.56 in CHCl3).
(d) Rongalite method
Dialkyl ditellurides (general procedure)5 Rongalite (9.24 g, 0.08 mol) and NaOH (9.0 g,
0.23 mol) are dissolved in distilled H2O (200 mL). The apparatus is flushed with N2
and finely powdered Te (15.3 g, 0.12 mol) is added. The mixture is stirred for 5 h and
then the alkyl bromide (0.12 mol) is added dropwise for 30 min with cooling and stirring. The solution is extracted with CCl4 (3⫻100 mL), and the extract is dried (CaCl2)
and distilled under vacuum, giving the dark red, foul-smelling ditelluride (R⫽Et, n-Bu,
n-pentyl, n-dodecyl).5,6
(e) TUDO method
Dialkyl ditellurides (general procedure).7 A mixture of powdered Te (0.128 g, 1 mmol) and
cetyltrimethylammonium bromide (CTAB, 0.004 g, 1.1⫻10⫺5 mmol) in THF (0.75 mL)
and DMSO (0.5 mL) is purged with a flux of deoxygenated N2 for 15 min and then heated
at 80°C. TUDO (0.1 g, 1 mmol) and NaOH (0.112 g, 2.6 mmol) in H2O (0.75 mL) are
added. The mixture is refluxed for 1 h and then the purple solution is cooled at 15°C. The
alkyl halide (2 mmol) is added and the mixture is stirred at room temperature for 1 h.
Normal work-up and filtration through a pad of Celite® (using CH2Cl2 as the mobile phase)
give the ditellurides as dark red oils (R⫽n-C11H23, n-C8H17, Me2CHCH2CH2, 2-heptyl,
THPO(CH2)6 (93–98%)).
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39
( f ) Sodium borohydride method
Dioctyl ditelluride (typical procedure)8 Na (0.10 g, 4 mmol) in small pieces is added to
a suspension of Te (0.50 g, 4 mmol) in absolute ethanol (50 mL), under N2 and with stirring. When the Na is dissolved, NaBH4 (0.075 g, 2 mmol) is added and the mixture heated
under N2 for 2 h, using a heating mantle. The mixture is cooled at room temperature and
neat octyl bromide (0.72 g, 4 mmol) is slowly added while stirring and cooling in an ice
bath. After stirring for 30 min, the mixture is poured into distilled H2O (100 mL), extracted
with ether (2⫻40 mL) and the combined extracts are dried. The solvent is evaporated
under vacuum and the residue is recrystallized from ether (by cooling at ⫺78°C) (0.77 g
(85%); m.p. 9°C).
(g) Hydrazine hydrate method
Dialkyl ditellurides (general procedure).9 Powdered Te (6.35 g, 50 mmol) is added to a
stirred solution of NaOH (3.0 g, 75 mmol) in deoxygenated H2O (20 mL). The mixture is
cooled in a water bath, and 100% hydrazine hydrate (2.5 g, 200 mmol) is added over a
period of 30 min and stirring is continued for an additional hour at room temperature. The
alkyl halide (50 mmol) is then added dropwise over a period of 2–3 h. During the addition,
the temperature is maintained at 15–20°C. The end-point of the alkylation is indicated by
a sharp colour change from dark brown to nearly colourless. The mixture is then extracted
with ether, the organic layer is washed with H2O, dried (Na2SO4) and the solvent removed
by slow distillation. The residue is distilled under vacuum.
3.2.1.2
From sodium ditelluride and aryl halides
The low reactivity of aryl halides towards nucleophilic reagents makes their reaction
with sodium ditelluride unattractive for the preparation of diaryl ditellurides. Low yields
are obtained, like the similar reaction with sodium telluride (see Section 3.1.2.1).
Na2Te2 + 2ArX
HMPA
ArTeTeAr
DMF
(5 - 40%)
Ar = Ph, 1- naphthyl, 2 - naphthyl, 9 -antracenyl
Di-2-naphthyl ditelluride (typical procedure).10 2-Chloronaphthalene (2 mol equiv) is
added to Na2Te2 (prepared by heating equimolar amounts of Te and Na in HMPA under
N2). The mixture is heated at 130–170°C for 16–24 h (yield 20%; m.p. 116–118°C, recrystallized from hexane).
This method was later revised replacing sodium ditelluride by potassium ditelluride.11
K2Te2
RTeTeR
Te/ KOH/ H2NNH2
45, 38%
80- 90°C, 2 h
R = Et, Me
RX
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3.2.2
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3. PREPARATION OF THE PRINCIPAL CLASSES OF ORGANIC TELLURIUM
By oxidation of organotellurols or organotellurolates
Organyl tellurolates, obtained by the insertion of elemental tellurium in organyllithium (or
magnesium) reagents (used as starting materials to prepare unsymmetrical tellurides as
shown in Section 3.1.3.2), can be oxidatively converted into the corresponding ditellurides.
This general method can be performed by direct oxidation of the tellurolates or through a
previous hydrolysis to the tellurols.
RMet
Te
R = alkyl, aryl
Met = Li(MgX)
RTeMet
H+
air
RTeH
air
RTeTeR
The Grignard route to diorganyl ditellurides suffers from lack of generality and the
mechanism of the oxidation seems to be uncertain. Alkylmagnesium halides demonstrate
lack of reactivity towards elemental tellurium,12 whereas arylmagnesium halides in ether
as the solvent furnish a mixture of ditellurides and tellurides.13 Satisfactory results are
obtained by tellurium insertion in arylmagnesium halides in THF followed by oxidation
before or after aqueous work-up.12,14,15
Bis(m-methoxyphenyl) ditelluride (typical procedure).14 To a stirred solution of m-bromoanisole (3.74 g, 20 mmol) in dry THF (80 mL) under N2 are added Mg turnings
(0.49 g, 20 mmol) at room temperature. The mixture is heated under reflux until most of
the Mg is dissolved. The Grignard reagent solution is cooled to room temperature and
well-powdered Te metal is added. After 0.5 h most of the metal will have dissolved. The
reaction mixture is then saturated with dry air at room temperature. The m-methoxyphenyl
ditelluride is obtained after routine work-up as a red oil (2.96 g (63.0%)).
Bis(p-methoxyphenyl) ditelluride (typical procedure).15 To a solurion of p-methoxyphenylmagnesium bromide (prepared from p-bromoanisole (5.82 g, 0.0311 mol) and Mg (1.0 g,
0.042 mol) in THF (20 mL)) is added Te shot (3.81 g, 0.0300 mol) at room temperature.
The mixture is stirred under reflux for 3 h and then cooled to 0°C and treated with a saturated solution of NH4Cl (20 mL; vigorous evolution of gas). The mixture is filtered through
Celite® and the solids washed with saturated solution of NH4Cl and ether. The organic phase
is washed with brine and dried with Na2SO4. Evaporation of the solvent and recrystallization from CHCl3/petroleum ether affords the pure product (5.16 g (75%); m.p. 57–59°C).
Early experiments to prepare diaryl ditellurides, employing aryllithium reagents generated by lithium–halogen exchange using ether as the solvent, gave only modest yields.16,17
At present the most successful and general route to dialkyl and diaryl ditellurides
employs the telluration of organyllithium compounds in THF.
Di-n-butyl ditelluride (typical procedure).18 n-Butyllithium (8.0 mL, 2.15 M in hexane;
17.2 mmol) is added dropwise at room temperature under N2 to a stirred suspension of
finely ground elemental Te (1.9 g, 14.9 mmol) in dry THF (50 mL). After 15 min all the
Te has been consumed, and the resulting yellowish solution is diluted with H2O (200 mL).
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DIORGANYL DITELLURIDES
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41
Air is then bubbled through it to oxidize the lithium tellurolate. The red oily ditelluride that
separates is extracted with ethyl ether (200 mL). The organic phase is washed with H2O
(2⫻50 mL), dried (CaCl2) and evaporated to give 2.83 g of a viscous red oil. Distillation
of 5.66 g of the crude material prepared in this manner affords 4.87 g of pure di-n-butyl
ditelluride (89% based on Te; b.p. 103–105°C/0.8 torr).
Di-t-butyl ditelluride is prepared in the same manner.
Diphenyl ditelluride (typical procedure).19 To a suspension of powdered Te (25.5 g,
0.2 mol) in anhydrous THF (300 mL), 2.0 M phenyllithium (100 mL, 0.2 mol) is added
dropwise, with stirring and under argon. The resultant mixture is stirred at room temperature for 2 h and under reflux for 1 h. The reaction mixture, which should contain only a
small amount of unreacted Te, is allowed to cool to 20°C, and is poured into 1 L of H2O.
Oxygen (or air) is bubbled for 1 h through the mixture, which is then extracted with
benzene (100 mL). The benzene solution is washed three times with H2O, dried (Na2SO4)
and evaporated. The residue is recrystallized from EtOH (77%; m.p. 63.8–65.0°C).
Di-2-thienyl and di-2-furyl ditelluride are prepared from thiophene and furan by lithiation with n-buthyllithium, tellurium insertion and oxidative work-up.17
Di-2-thienyl ditelluride (typical procedure).17 n-Butyllithium (11.0 mL, 2.2 M, 24.2 mmol)
is added to an ice-cooled stirred solution of thiophene (2.0 g, 23.8 mmol) in dry THF
(50 mL). After 10 min at 0°C and 50 min at room temperature, elemental Te (2.9 g,
22.7 mmol) is added rapidly. All Te is completely dissolved after 30 min, when the yellowish
solution is poured into a beaker containing H2O (300 mL). CH2Cl2 (200 mL) is then added
and air passed through the two-phase system for 1 h. To effect complete oxidation, the
beaker is left overnight in the open air. The organic phase is separated and the aqueous
phase extracted several times with CH2Cl2. The combined organic extracts are dried
(CaCl2) and evaporated to give a red solid. Recrystallization from EtOH affords 3.54 g
(74%) of di-2-thienyl ditelluride (m.p. 89–90°C).
The preparation of aryllithium reagents can also be performed by using t-butyllithium
in a halogen–metal exchange, and aqueous potassium ferricyanide as an oxidant.17,20
Bis(p-methoxyphenyl) ditelluride (typical procedure).20 t-Butyllithium (10 mL, 1.7 M,
17.0 mmol) is added dropwise to a stirred solution of p-bromoanisole (1.59 g, 8.5 mmol)
in THF (40 mL) at ⫺78°C under argon. After 1 h the cooling bath is removed and the mixture allowed to warm to room temperature for 30 min. Finely ground Te (1.08 g, 8.5 mmol)
is then added rapidly while a brisk stream of argon is passed through the open system to
prevent admission of air. After 1 h, when only traces of Te remain, the mixture is poured
into a separating funnel containing K3Fe(CN)6 (2.80 g, 8.5 mmol) in H2O (150 mL). The
ditelluride product is extracted with CH2Cl2 (100 mL ⫹ 2⫻50 mL). After drying of the
combined extracts (CaCl2), evaporation on SiO2 (10 g) and flash chromatography (SiO2;
hexane/CH2Cl2, 8:2) give the ditelluride (0.99 g (50%); m.p. 58–59°C). The material is
recrystallized from EtOH.
The following diaryl ditelluride can be prepared in the same manner as in the foregoing
procedure: Ar⫽2-pyridyl, Ph an...