A Remarkable Difference in the Reactivity between cis- and trans-Silylplatinum Complexes toword Insertion of Acetylene

Reaction of cis-PtMe(SiPh3)(PMe2Ph)2 (1) with phenylacetylene in benzene readily proceeds at room temperature to give the acetylene-insertion product cis-PtMe{C(Ph)=CH(SiPh3)}(PMe2Ph)2, while trans-PtMe(SiPh3)(PMe2Ph)2 (2), which is the geometrical isomer of 1, is inactive toward acetylene-insertion. A mechanism of insertion involving a five-coordinate intermediate is proposed to account for the marked difference in the reactivity between the cis and trans isomers.