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Experiment 9
Preparation of -Arene Ruthenium
Complexes
-Arene Ruthenium Complexes - 1
Experiment 9: Preparation of -Arene Ruthenium
Complexes
Aims
to prepare -arene ruthenium complexes.
to examine their structures
to compare the structures with other close analogues
to interpret NMR and IR spectra
Introduction
Transition metal complexes with organic -ligands are a hugely important class of
organometallic compounds. A wide variety of unsaturated organic molecules (eg alkenes,
alkynes, butadienes and arenes) or ions (eg allyls, cyclopentadienyls) can act as -ligands as
shown in the examples below:
CO
OC
Fe
C
O
Mo
Cl
C
Fe
OC
CO
OC
CO
CO
O
Many of these organic species are reactive and can undergo a variety of reactions, while
others tend to be spectator ligands. -arenes can behave in both ways. Benzene rings are
activated towards nucleophilic substitution when -bonded to metals and are more readily and
more selectively metallated. In the example here the -arene is a spectator ligand, covering
one face of the metal.
Experimental
a) Preparation of [(6-p-cymene)RuCl2]2
- Prepare a solution of RuCl3.H2O (0.35 g) in ethanol (15 cm3) and add -terpinene (1-methyl4-isopropylcyclohexadiene, 2.5 cm3).
CARE – Avoid contact of RuCl3 with your skin – it stains. Also, RuCl3 is very hydroscopic
– do not leave the bottle open for more than a few seconds at a time.
- Heat to reflux for the remainder of the laboratory session.
- Allow to cool to room temperature overnight.
- The next day, filter off the red-brown product, wash with methanol and diethyl ether.
- Record the yield (g, %).
NOTE: The filtrate contains ruthenium and should not be put down the sink. A ruthenium
waste bottle is provided – please use it.
b) Reaction of [(6-p-cymene)RuCl2]2 with PPh3
- Dissolve [(6-p-cymene)RuCl2]2 (0.1 g) in chloroform (10 cm3) and add triphenyl phosphine
(0.085 g).
- Stir for 1 hour at reflux and cool to room temperature.
- Remove the solvent on the rotary evaporator and wash the sticky solid with diethyl ether (5
cm3), discarding the washings.
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- Dissolve the product in dichloromethane (2 cm 3) and transfer the resulting solution by
dropping pipette to a small sample vial.
- Very carefully, add diethyl ether (12-15 cm3) in such a way that two layers form.
NOTE: The best way to do this is to add the diethyl ether from a dropping pipette, allowing
it to run very slowly down the wall of the sample bottle. The density of the ruthenium
solution is much greater than that of the ether and so if you are careful they won’t mix
significantly. Be patient, for the first 5 cm3 or so it doesn’t look like the two layers are
separating, but it will eventually look OK. Slow diffusion of the ether into the
dichloromethane solution results in very slow crystallisation of the product and thus you
should obtain quite large crystals. This method of crystallisation is called twin layer
diffusion and is often used to prepare crystals suitable for single crystal X-ray diffraction
experiments.
- Carefully put the cap on the sample vial and move to a still place (e.g. your cupboard)
without mixing the two layers.
- Allow to stand overnight for crystallisation to complete.
- The following day, carefully remove most of the solvent using a dropping pipette and add
diethyl ether to cover the crystals.
- With a small spatula gently scrape the crystals from the wall of the vial and filter off.
- Dry in air.
- Record the yield (g, %).
c) Investigation
- Using the program ORTEP inspect the crystal structures of the two compounds.
- Search for the structures of the two products and related compounds on the Crystallographic
database. (You can do this on day 1 while the reflux is progressing).
- Run Infra-red spectra of your samples as nujol mulls.
- Show your samples to a demonstrator who will give you NMR spectra.
Questions
1.
2.
3.
4.
Draw reaction schemes to describe your reactions.
Describe the important features of the crystal structures of these compounds and
compare them with other examples that you found during your search.
Interpret your NMR and IR spectra as fully as possible. Why are the benzene ring
protons at such low chemical shift values (compared to free p-cymene)?
What is the electron count of [(p-cymene)RuCl2(PPh3)]?
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