Mechanistic Study on the Insertion of Phenylacetylene into cis-Bis(silyl)platinum(II) Complexes

Four bis(silyl)platinum complexes cis -Pt(SiR 3 ) 2 (PMe 2 Ph) 2 (SiR 3 = SiMe 2 Ph ( 1a ), SiMePh 2 ( 1b ), SiPh 3 ( 1c ), SiFPh 2 ( 1d )) have been prepared and their reactions with alkynes and alkenes examined. The X-ray structures of 1a − c exhibit significant distortion from the square planar geometry in the order 1b > 1c > 1a . Complexes 1a − d react with phenylacetylene in solution to give the corresponding insertion complexes cis -Pt{C(Ph) CH(SiR 3 )}(SiR 3 )(PMe 2 Ph) 2 ( 2a − d ). Complex 1c reacts also with acetylene to afford the insertion complex cis -Pt(CH CHSiPh 3 )(SiPh 3 )(PMe 2 Ph) 2 ( 2e ), whose structure has been determined by X-ray diffraction study. Kinetic studies indicate the insertion process involving prior dissociation of PMe 2 Ph ligand from 1, followed by insertion of phenylacetylene into the Pt−SiR 3 bond. The reactivity toward insertion decreases in the order 1c > 1a > 1b ≫ 1d . Factors responsible for the reactivity order are discussed on the basis of kinetic data and X-ray structures.