Hydrogen migrations in rhodium silyl complexes: Silylene intermediates vs oxidative Addition/Reductive elimination

Reaction of (PMe3)(4)RhMe with H2SiPh2 results in elimination of CH4 and generation of the rhodium silyl complex (Me3P)(4)RhSiHPh2 (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)(3)RhSiHPh2 (2). Reaction of (Me3P)(3)RhCl with (THF)(2)LiSiHMes(2) (Mes = 2,4,6-trimethylphenyl) in toluene resulted in formation of the metalated species fac-(Me3P)(3)Rh(H)Si(H)(Mes)C6H2Me2CH2 (3), which was characterized by X-ray crystallography. Compound 3 was also prepared by the reaction of (Me3P)(4)RhMe with H(2)SiMes(2). The reaction of (Me3P)(4)RhMe with 1 equiv of D(2)SiMes(2) 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.