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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
Ligand effects on reactivity of cobalt acyl complexes
ACS Catalysis, Volume 2, No. 12, Year 2012
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Description
Hydrogenolysis reactions of cobalt acyl complexes, [Co(CO) 3(L)(COR)] (L = phosphine, R = Me, nPr) have been monitored using in situ IR spectroscopy at moderate temperatures (<75 °C) and pressures (<25 bar). The reactions provide a model for the product-formation step in phosphine-modified, cobalt-catalyzed hydroformylation. The reaction kinetics are dependent on L, with the fastest rate being observed for the complex containing n-pentyl-9-phosphabicyclo[4.2.1]nonane (a 5-PhobPC5). The observed dependence of rate on H 2 and CO pressure is consistent with a mechanism involving initial CO dissociation, followed by reaction of [Co(CO)2(L)(COR)] with H 2. Isotopic exchange experiments, monitored by IR spectroscopy, demonstrate that both terminal and acetyl carbonyls of [Co(CO) 3(L)(COR)] exchange with free 13CO. Kinetic data are also reported for reactions of [Co(CO)3(L)(COR)] with triphenyltinhydride. A zero-order dependence on [Ph3SnH] (at large excess) and positive values of ΔS‡ demonstrate rate-determining CO dissociation. For a series of less bulky, symmetrical phosphines, the rates follow the sequence PEt3 < PMe2Ph ∼ PEtPh 2 < PPh3 < P(4-ClC6H4) 3, in accord with their electron-donating strength. Higher rates are found for more bulky phosphines, and the fastest rate is again found for L = a5-PhobPC5. Calculations using density functional theory indicate that the CO dissociation energy for [Co(CO)3(L)(COMe)] is influenced by the stereoelectronic properties of L, with steric bulk having a substantial effect. X-ray crystal structures are reported for [Co(CO) 3(PEtPh2)(COMe)], [Co(CO)3(s-PhobPC 5)]2, and [Co(CO)3(a5-PhobPC 5)]2. © 2012 American Chemical Society.
Authors & Co-Authors
Birbeck, James M.
United Kingdom, Sheffield
The University of Sheffield
Haynes, Anthony
United Kingdom, Sheffield
The University of Sheffield
Adams, Harry
United Kingdom, Sheffield
The University of Sheffield
Damoense, Llewellyn J.
South Africa, Sasolburg
Sasol Technology Pty Ltd
Otto, Stefanus F.
South Africa, Sasolburg
Sasol Technology Pty Ltd
Statistics
Citations: 23
Authors: 5
Affiliations: 2
Identifiers
Doi:
10.1021/cs300589n
ISSN:
21555435