Transition Metal Induced Topotactic C-C Bond Formation

The thermolyses of dichlorobis-(1-phenyl-3,4-dimethylphosphole) platinum (II), 1, and dichlorobis-(1-phenyl-3,4-dimethylphosphople) palladium (In, 2, were investigated in 1,1,2,2-tetrachloroethane solutions and in the crystalline state. The solid state reactions show a high degree of topotacticity and probably involve 1,4-biradical intermediates. Three compounds are formed upon thermolysis of 1 in 1,1,2,2-tetrachloloethane at 142°C (scheme I): a [4+2] cycloaddition product, 3; a [2+2] cycloaddition product, 4, and a compound, 5, that results from 1,5-hydrogen migration from a methyl group on one phosphole to the β-carbon of an adjacent phosphole. Only 5 is ultimately formed in quantitative yield from 1 after 24 hours at 150°C in the solid state.