Chem 410 Lab Report Guidelines for
Experiment #9 – Synthesis and Reactivity of Vaska’s Complex
Experiment #9 can be found on p. 189 of the laboratory manual.
Please use the lab report templates available on Blackboard prepare a report based on your
assigned section (please see table below).
Due Date
Experiment
4/12/19
9
Abstract
Lab Report Section Assignment
Results &
Introduction Experimental
Discussion
3,8,13
4,9,14
5,10,15
1,6,11
Conclusions
2,7,12
Questions to be Answered:
1) How does the νCO stretching frequency of coordinated CO compare with free CO (2143
cm-1), and how can the difference be explained in terms of bonding (σ and π) with the
metal?
2) What is the importance oxidative additions in catalysis?
3) How much does it cost to purchase IrCl3•3H2O and Vaska’s complex? Evaluate the total
cost of the materials used in your synthesis.
4) What is the role of aniline in the synthesis of Vaska’s complex?
Data to be included in Supporting Information:
1)
2)
3)
4)
5)
Cover page with Table of Contents
IR spectra of products
Sample % yield calculations
NMR Spectra of products
Carbon copies from lab notebook
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Table of Contents Graphic (TOC)
3
EXPERIMENT 19
d IR
Microscale Synthesis of Vaska's Complex
1, 20.
IrCI(CO)[P(C6H5)3]2
V. L
Hal:
BI
1989
tma-
G.;
**This experiment requires about 6 hours spread over two laboratory periods.
The exament will introduce you to the use of microscale techniques, the
ang O compounds on a scale of 100 mg or less. One of the advantages of
BRZle synthesis is the low cost of working with small amounts of reagents
breats. This consideration is particularly important in this experiment,
We are that evaporations and filtrations proceed more quickly than with
ih uy the expensive metal iridium. Other advantages of microscale tech-
2. with practice, microscale syntheses are easier than gram-scale chemistry so
macational scale synthesis, and reaction wastes are minimized. You will find
Se ik number of transfers and to use small reaction vessels.
wants of the sample adhering to the apparatus. Thus it is important to mim-
is the
Con
bonyl
York,
US-
Many important concepts in organometallic chemistry relevant to reactivity
and catalysis are illustrated by the behavior of the complex prepared in this
exrimenttrans-chlorocarbonyibis(triphenylphosphine)iridium(I). Or
taco)PC Hs)s). This compound is called Vaska's complex in recognition of
researcher who first demonstrated its versatile chemical properties,
Vaska's complex is a square planar complex of iridium(1) with trans-triphenyl-
peine ligands:
1993,
from
stuna
o
2. G:
Try of
(CoHs)3P
>
P(CH3)3
El
6
ntary
Vaska's complex nicely illustrates the concept that the reactivity of a metal
caplex is related to its valence electron count. Complexes with 18 valence elec-
New
vers are called saturated and generally do not bind other ligands. Compleres
fa 16 valence electrons, such as Vaska's complex, are unsaturated and able to
A certain two-electron donors, L, to form adducts:
hemi
ation
*2370-
I-CH(COJIP(C2Hslala
Ircl{co){P{C;Hs)al24
+ L
189
spray
18 e complex
16 € complex
Part 1V / ORGANOMETALLIC CHEMISTRY
EXP
192
Note
reacts with the compound. If you examine the spectrum of IrCl(COP(Hsbla
a KBr pellet, you should consider the possibility that Brº/Cl- exchange occurs to
The most prominent absorption in the IR spectrum of Vaska's complex is the
carbonyl (CO) stretching band, which is usually symbolized vco. The vibrational
frequency of CO ligands is sensitive to the electronic properties of the metal center
quan
form IrBr(CO)/P(C6H3);.
hana
by virtue of the overlap of the CO n' orbital with metal d orbitals:
BOIS
e
e
Biser
In a
plaa
mmo
anili
bubb
of N
altit
yield
Iridium(1) - CO
Interaction
Iridium(III) - CO
Interaction
of m
yello
each
prod
Oxy
In a
of 10
Generally, the transfer of electron density from the metal to the CO T* orbital
is more efficient when the metal is in a low oxidation state. This transfer of elec-
tron density, called a back-bonding, strengthens the M-C bond and weakens the
C-0 bond because the gº orbital is antibonding with respect to C and O. This
logic suggests that the ico frequency in CO complexes will decrease as more
back-bonding occurs. These concepts are important for analyzing the bonding
between metals and CO; the bonding of many other ligands, including alkenes,
acetylenes, N3, and isocyanides, can be analyzed in a similar way.
The characterization of CO complexes by IR spectroscopy is very convenient
because the CO stretching bands occur in a region where fèw organic molecules
absorb. Furthermore, co stretching bands are usually rather intense; con-
sequently, it is possible to record spectra from extremely dilute solutions. The roo
bands of metal carbonyls are even more intense than the ico bands seen for
organic carbonyls such as ketones and esters,
The voo band for the iridium(I) compound IrCl(CO)P(C6Hs);}; is found
near 1960 cm -, whereas in the iridium(III) compound IrCl3(CO)[PC Hshh it
appears at 2120 cm). This frequency shift indicates that the C-o bond is
stronger (and the Ir-C bond weaker) in the latter complex. For the O, complex
IrCl(CO)[P(C6Hshl:(03) the CO stretching band occurs at 2010 cm
suggests that the O, ligand withdraws electron density less effectively than
two chloride ligands
. In the present experiment, the relative amounts of
Ircico)P(C6H,)sh and Ircico[PC Hs);};(0) can be estimated from the
relative intensities of the yco bands at 1960 and 2010 cm
CUSSI
then
the
resid
mits
sirea
resid
IR S
This
1. P
which
2. A
Thuis
Experiment 19 Microscale Synthesis of Vaska's Complex IrCi(CO) P(Cehshalz
193
EXPERIMENTAL PROCEDURE
Vole: Indium salts can cost up to US$100 per gram, so it is essential to use small
quantities in this experiment. When small amounts of compounds are being
handled, it is important to minimize mechanical losses by using small reaction
vessels and by reducing the number of times the sample is transferred,
lo
en
cale
trans-IrCi(CO)[P(CHz)sk
In a 50-mL round-bottom flask mounted in a rheostat-controlled heating mantle,
place a Tefion-coated stir bar, 0.105 g (0.3 mmol) of LC13-3 H20,* 0,393 g (I.S
mmol) of triphenylphosphine, 10 mL of dimethylformamide, and 0.120 mL of
aniline. Fit the flask with a reflux condenser topped with a N, inlet connected to a
bubbler. Briefly flush she air from the system with a Nz stream. Decrease the fios
Teing kept
-1000
around /
of Nz gas and heat the mixture to vigorous reflux for 2 h (or longer at higher
altitudes). Heating can be continued for up to 24 h without adversely affecting the
yield
. Allow the yellow solution to cool to 50 °C (or below) and then add 30 ml
of methanol. Cool the mixture in an ice bath for 10 min and then collect the
yellow microcrystals by filtration in air. Wash the crystals with a few milliliters
each of methanol and diethyl ether, and then dry the solid in a vacuum. Solid
samples of Vaska's complex are air stable. Record the yield, and save some of the
product for an IR spectrum.
NMR sal
in Chlorate
ge
Oxygeaation of IrCKCO)[P(CsHsbh2
In a 100-ml Schlenk flask containing a magnetic stirring bar, prepare a solution
of 40 mg of Vaska's complex in 20 mL of toluene (see Experiment 17 for a dis-
cussion of Schlenkware). While stirring the solution, flush the fask with O, gas,
then close off the stopcock and stopper the fiask. Vigorously stir the solution in
the O2 atmosphere for 90 min. Evaporate the solution to obtain a yellow-orange
residue. Record the IR spectrum of some of the solid as a Nujol mull. Time per-
mitting, redissolve the remainder in toluene and purge the solution again with a
Stream of N, gas. Once the solvent has evaporated, remove some of the solid
residue and examine ils IR spectrum.
pt
IR Spectra as Nujol Mulls
This section describes in detail a method for preparing mulls of compounds.
1. Put about 5 mg of the complex in a polished agate mortar and grind the
sample with an agate pestle until the substance forms a glossy layer in the
mortar (between 1 and 5 min of grinding). The extent of grinding will make
the difference between a good and a bad spectrum.
2. Add a small drop of the Nujol (or other mulling agent) to the lip of the mor-
lar, With the pestle, transfer a small amount of the mulling agent to the
powder, Grind this mixture, adding more mulling agent il necessary.
all of the sample has been converted into a paste.
Roure la cucle sunt 431 Un me BUDO sites she
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