Polymer-Bound Iridium Catalysis. Hydrogen Transfer from Formic Acid to Unsaturated Carbon-Carbon Bounds

Article abstract of DOI:10.1021/jo00182a002

Polystyrene-bound IrCl(CO)(PPh3)2 promotes hydrogen transfer from formic acid to a variety of olefinic substances.The activity of the catalyst increases after the first few uses during which time a substrate-iridium complex is formed.Detailed kinetic studies were carried out with benzylideneacetophenone as the hydrogen acceptor.The catalysis is assumed to proceed by the following steps: (a) cleavage (dissociation) of an Ir-P bond in the supported complex <*>(PPh2)2IrCl(CO); (b) coordination of the acceptor at the vacated site; (c) oxidative addition of formic acid followed by olefin insertion leading to the formation of an iridium oxopropenyl formate complex; (d) hydrogen transfer from the formate to the iridium accompanied by loss of carbon dioxide; (e) reductive elimination to give the final product.Step d is considered rate determining on the basis of kinetic isotope effect measurements with HCOOD, DCOOH, and DCOOD.The catalytic activity of the system is decreased by swelling solvents and increased by nonswelling ones.The fully activated, supported catalyst is air stable, essentially leach proof, and capable of being used for an unlimited number of catalytic cycles.