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Mono- and binuclear cobalt hydrides

The homogeneous hydrogenation of arenes with functional groups was studied with allylcobalt complexes containing the bulky chelating diphosphines dippp (1,3-bis(diisopropylphosphino)propane and dippcyp (trans-(±)-l,2-bis(diisopropylphos-phino)cyclopentane). The results indicated that these catalyst precursors were unsuitable for the hydrogenation reactions, being too sensitive to the nature of the substrate. From these hydrogenation reactions, the intermediates (η⁵-cyclohexadienyl)Co(dippcyp) (10) and (η⁴-2-methoxynaphthalene)Co(H)(dippcyp) (11) were isolated and structurally characterized, thus providing some insight into the mechanism of the hydrogenation reaction.
The production of binuclear hydrides such as [(dippp)CoH₂]₂ (4) and [(dippcyp)CoH₂]₂ (9) was observed to lead to the end of the catalysis. An X-ray structural characterization of the blue hydride [(dippp)CoH₂]₂ (4) showed that in the solid state it is binuclear. Although the complex is diamagnetic in the solid state (6-280 K), in solution its paramagnetic behaviour could only be attributed to an equilibrium with a second species proposed to be mononuclear, (dippp)CoH₂. In addition, a cyclic voltammogram of the complex in solution indicated that the predominant species still was the binuclear compound [(dippp)CoH₂]₂ (4).
One of the syntheses of [(dippp)CoH₂]₂ (4) gave a product identified as (dippp)CoH₃ (5). Based on variable-temperature spin-lattice relaxation time (T₁) measurements and an electrochemical study, this red hydride complex appeared to contain an η²-H₂ ligand. The relationship of this complex with the blue hydride apparently involves the mononuclear species, (dippp)CoH₂. Independent pathways led to the formation of both the blue and red hydrides, and these pathways are discussed in terms of possible mechanisms. / Science, Faculty of / Chemistry, Department of / Graduate

Identiferoai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/30789
Date January 1990
CreatorsNg, Jesse B.
PublisherUniversity of British Columbia
Source SetsUniversity of British Columbia
LanguageEnglish
Detected LanguageEnglish
TypeText, Thesis/Dissertation
RightsFor non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.

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