Kinetic Studies on the Reductive Elimination of cis-PtMe(SiPh₃)(PMe₂Ph)₂ and cis-PtMe(GePh₃)(PMe₂Ph)₂. The First Comparison between C−Si and C−Ge Reductive Elimination

The novel complex cis -PtMe(GePh 3 )(PMe 2 Ph) 2 ( 2b ) was prepared by the treatment of trans -PtCl(GePh 3 )(PMe 2 Ph) 2 ( 3 ) with 2 equiv of MeLi in THF followed by methanolysis of the reaction system. The X-ray and NMR data of 2b, together with the NMR data of related cis -PtMe(SiPh 3 )(PMe 2 Ph) 2 ( 1b ) and cis -PtMe 2 (PMe 2 Ph) 2 ( 4 ), indicated the following order of trans influence: SiPh 3 ≫ GePh 3 > Me. While the trans influence of the GePh 3 ligand is much lower than that of the SiPh 3 ligand and only slightly higher than that of the Me ligand, the GePh 3 ligand was found to possess a much higher trans effect than the methyl ligand, comparable to the SiPh 3 ligand. Thermolysis of 1b and 2b in toluene- d 8 in the presence of an excess amount of diphenylacetylene provided quantitative yields of reductive-elimination products MeSiPh 3 and MeGePh 3, respectively. Kinetic studies revealed that the methyl−germyl complex 2b is much more stable than the methyl−silyl complex 1b . The reductive elimination proceeds for both complexes via a process involving a prior ligand displacement of one of the PMe 2 Ph ligands with diphenylacetylene, followed by elimination of MeSiPh 3 or MeGePh 3 from the resulting acetylene-coordinated species. Factors governing the reactivity of C−Si and C−Ge reductive elimination from a Pt(II) center are discussed.