Reactions of free radicals with η 3-allylpalladium(II) complexes: cyclohexyl radicals

Abstract

Allyl palladium complexes of the types [(η 3-allyl)PdCl] 2, (η 3-allyl)PdCl(PPh 3) and [(η 3-allyl)Pd(PPh 3) 2]Cl (allyl=C 3H 5, 1-MeC 3H 4, 2-MeC 3H 4, 1-PhC 3H 4, 2-PhC 3H 4) react with cyclohexyl radicals derived from the visible light photolysis of (c-hex)Co(DMG) 2(py). The reactions proceed via initial attack of the free radical at the metal center, followed by β-hydrogen elimination and subsequent reductive elimination of propene, 1-butene, isobutene, 3-phenylpropene and 2-phenylpropene, respectively. The 3-phenylpropene can be catalytically isomerized to the thermodynamically more stable 1-phenylpropene by either palladium metal or palladium(0) products, but the formation of 1-butene and 3-phenylpropene as primary products is unusual. A mechanism, differing in many ways from that proposed previously for analogous reactions of phenyl and trityl radicals, is proposed for the overall reaction and supported by use of the labeled cobaloxime, (2,2,6,6-D 4-c-hex)Co(DMG) 2(py).