Reactions of cis- and trans-Silyl(methyl)platinum(II) Complexes with Phenylacetylene. Remarkable Effect of Cis and Trans Configurations on the Reactivity

Two geometrical isomers of silyl(methyl)platinum complexes cis - and trans -PtMe(SiPh 3 )L 2 (L = PMe 2 Ph, PMePh 2 ) exhibited entirely different reactivities toward phenylacetylene. Reactions of cis -PtMe(SiPh 3 )L 2 (L = PMe 2 Ph ( 1a ), PMePh 2 ( 1b )) with phenylacetylene readily proceeded at room temperature in benzene to give the acetylene-insertion products cis -PtMe{C(Ph) CH(SiPh 3 )}L 2 (L = PMe 2 Ph ( 3a ), PMePh 2 ( 3b ), respectively). In contrast, trans -PtMe(SiPh 3 )L 2 complexes (L = PMe 2 Ph ( 2a ), PMePh 2 ( 2b )) were totally inactive toward acetylene insertion. The cis -organo(silyl)platinum complexes cis -PtMe(SiPh 3 )(PMe 3 )(PMePh 2 ) ( 1c ) and cis -Pt(COEt)(SiPh 3 )(PMe 2 Ph) 2 ( 6d ) also underwent the insertion of phenylacetylene into the Pt−SiPh 3 bond to provide quantitative yields of cis -PtMe{C(Ph) CH(SiPh 3 )}(PMe 3 )(PMePh 2 ) ( 3c ) and cis -Pt(COEt){C(Ph) CH(SiPh 3 )}(PMe 2 Ph) 2 ( 7 ), respectively. The molecular structures of 3a, c were determined by X-ray diffraction studies. Kinetic studies on the formation of 7 revealed the insertion process initiated by rate-determining displacement of one of the PMe 2 Ph ligands in 6d with phenylacetylene.