Hydrogen Migrations in Rhodium Silyl Complexes:  Silylene Intermediates vs Oxidative Addition/Reductive Elimination

Reaction of (PMe3)4RhMe with H2SiPh2 results in elimination of CH4 and generation of the rhodium silyl complex (Me3P)4RhSiHPh2 (1; 62% isolated yield). Compound 1, which appears to adopt a trigonal bipyramidal geometry with the silyl group in an axial position, is in equilibrium with the 16-electron complex (Me3P)3RhSiHPh2 (2). Reaction of (Me3P)3RhCl with (THF)2LiSiHMes2 (Mes = 2,4,6-trimethylphenyl) in toluene resulted in formation of the metalated which was characterized by X-ray crystallography. Compound 3 was also prepared by the reaction of (Me3P)4RhMe with H2SiMes2. The reaction of (Me3P)4RhMe with 1 equiv of D2SiMes2 in toluene resulted in distribution of deuterium between the Rh−H, SiH, RhCH2, and o-Me positions of 3. Since the rate of this equilibration is not reduced in the presence of excess PMe3, we propose that successive Si−H and C−H reductive-elimination/oxidative-addition cycles are responsible for the deuterium-scrambling process.