J. Knight, S. Doherty, A. Harriman
Oct 21, 2000
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0
Influential Citations
38
Citations
Journal
Organometallics
Abstract
The C4-bridged diphosphines cis- and trans-1,2-bis(diphenylphosphinomethyl)cyclohexane (cis, 1a; trans, 1b) and endo,endo-2,3-bis(diphenylphosphinomethyl)norbornane and exo,endo-2,3-bis(diphenylphosphinomethyl)norbornane (endo,endo, 1c; exo,endo, 1d) and their corresponding palladium complexes [(P−P)PdCl2] (2a−d), [(P−P)Pd(OAc)2] (3a−d), and [(P−P)PdMeCl] (P−P = 1a, 4a; P−P = 1c, 4c) have been prepared and characterized. Single-crystal X-ray analysis of 2a reveals that 1a forms a seven-membered chelate ring with the cis-disubstituted cyclohexyl ring in the expected chair conformation. Variable-temperature 31P{1H} NMR studies of 2a have revealed a dynamic process that interchanges stereoisomers via conformational changes in the six-membered ring, often characteristic of cis-disubstituted cyclohexane derivatives. The free energy of activation associated with this exchange has been determined (ΔG⧧ = 48 kJ mol-1, 2a). Variable-temperature 31P{1H} and 31P NOESY NMR studies have shown that 4a exist as an interc...