Dimeric Rhodium μ-Silylene and μ-η²-Silyl Complexes:  Catalytic Silicon−Silicon Bond Formation and X-ray Structures of [{Prⁱ₂PCH₂CH₂PPrⁱ₂}Rh]₂(μ-SiRR‘)₂ (R = R‘ = Ph and R = Me, R‘ = Ph) and [{Prⁱ₂PCH₂CH₂PPrⁱ₂}Rh(H)]₂(μ-η²-H−SiMe₂)₂

Abstract

The stoichiometric and catalytic reactions of secondary silanes with the rhodium hydride bridged dimer [(dippe)Rh]2(μ-H)2 (1; dippe = 1,2-bis(diisopropylphosphino)ethane) are described. The reaction of 1 with Ph2SiH2 results in the formation of the bis(μ-silylene) complex [(dippe)Rh]2(μ-SiPh2)2 (2a); a similar reaction ensues upon addition of MePhSiH2 or MepTolSiH2 (pTol = p-tolyl) to 1 except that the bis(silylene) complexes exist as a mixture of cis and trans stereoisomers. Dimethylsilane reacts with 1 to generate the dinuclear complex [(dippe)Rh(H)]2(μ-η2-H−SiMe2)2 (4d). The hydride dimer acts as a catalyst precursor for the dimerization of excess Ph2SiH2 to tetraphenyldisilane (Ph2SiHSiHPh2). A catalytic cycle is proposed that consists of dinuclear intermediates.