<p> Dicobalt octacarbonyl reacts with a wide variety of
molecules containing trichloromethyl functionalities to
yield carbynyl tricobalt nonacarbonyl clusters of the
general formula R-CCo 3 (CO) 9 . While these clusters have
been shown to undergo many reactions, mechanistic studies
on these systems are sparse. In particular, their rather
facile decarbonylation processes are not well understood. </p> <p> Complexes of the type Ar-CO-CCo 3 (CO)9 readily lose CO
to produce the corresponding Ar-CCo 3 (C0) 9 clusters but
the origin of the carbon monoxide extruded was not known .
Speculation had focussed on two possibilities: firstly,
direct elimination of the ketonic carbonyl - perhaps via
radical intermediates - and, secondly, via initial loss
of a cobalt carbonyl ligand (to produce a 16-electron
cobalt vertex) with subsequent migration of the original
ketonic group onto the coordinatively unsaturated cobalt
center. These two mechanistic possibilities are differentiable
by labelling either the cobalt carbonyl sites or
the ketonic position with carbon-13 and then examining
the decarbonylated product to locate the isotopically
enriched positions by 13c NMR spectroscopy. It is shown
that the carbon monoxide initially eliminated is a cobalt
carbonyl and the ketonic CO migrates from its apical
position onto a cobalt atom. </p> <p> A second project involves the synthesis and characterization
of a cobalt cluster derived from the reaction of dicobalt octacarbonyl with the insecticide DDT . This
cluster contains the bis(4-chlorophenyl)methylcarbynyl
capping group which is so bulky that it has the potential
to stop the rotation of the carbynyl ligand and also
prevent carbonyl exchange on the metal triangle. The
DDT-tricobalt cluster was characterized by X-ray crystallography.
The compound crystallizes in the space group
P21/n: the monoclinic cell has dimensions a = 13.083 A,
b = 14.222 A, c = 14.165 A, B = 95.871 degrees and Z = 4. The
molecule adopts almost Cs symmetry except that the phenyl
rings are twisted slightly so as to destroy the potential
mirror plane. At low temperature, the cobalt carbonyl
ligands are non-equivalent on the NMR time-scale and the
possible causes for this behaviour are discussed. </p> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19381 |
| Date | 03 1900 |
| Creators | Gates, Reginald |
| Contributors | McGlinchey, M. J., Chemistry |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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