Reactions of Dienes with the Ion +: A Kinetic and Mechanistic Study of Complex Formation and Diene Hydrogenation

DOI: 10.1039/DT9840001171

Source and publish data:

Journal of the Chemical Society, Dalton Transactions p. 1171 - 1180 (1984)

Update date:2022-08-04

Topics:

Authors:

Howarth, Oliver W.

McAteer, Colin H.

Moore, Peter

Morris, George E.

Read Full Text PDF DownLoad Join now for total 90,000,000 free articles

Article abstract of DOI:10.1039/DT9840001171

Stopped-flow n.m.r. reveals markedly different rates of co-ordination of cyclo-octa-1,5-diene (cod) and bicyclo<2.2.1>hepta-2,5-diene (norbornadiene, nbd) to the ion ⁺ (1). ⁺ ions are the first formed products.The interconversion of all three ⁺ isomers has been observed by 1H and 31P n.m.r. sprectroscopy.These species react further to give ⁺ (2), either by H2 elimination, or by hydrogenation of the co-ordinated nbd to form bicyclo<2.2.1>hept-2-ene (norbornene, nbe).Stopped-flow spectrophotometry reveals a marked inverse kinetic isotope effect for the formation of (2) during the hydrogenation or deuteriation of nbd.A mechanism involving an equilibrium between diene-dihydride and alkyl-hydride is proposed.The dienes 2,3-dimethylbutadiene and cyclohexa-1,3- or -1,4-diene react with (1) to give highly fluxional allyl-hydride species which feature an aliphatic C-H...Ir^III interaction.Variable-temperature 1H and 31P n.m.r., and 1H spin-saturation transfer experiments reveal a facile reversible hydrogen-transfer process between metal and hydrocarbon ligand which occurs via a C-H...Ir^III interaction.