Synthesis, structure, and reactivity of {(2-phosphinoethyl)silyl}rhodium(i) complexes Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)n (n = 2, 3)

Abstract

A (2-phosphinoethyl)silylrhodium(III) complex RhH(Cl)[(κ²Si,P)-Me₂Si(CH₂)₂PPh₂](PMe₃)₂ (1) was synthesized by the thermal reaction of RhCl(PMe₃)_n (n = 3, 4) with HMe₂Si(CH)₂PPh₂ at 50 °C for 2 h. Treatment of 1 with MeLi gave a coordinatively unsaturated rhodium(I) complex Rh[(κ²Si,P)-Me₂Si(CH₂)₂PPh₂](PMe₃)₂ (2) which was possibly produced via transient formation of RhH(Me)[(κ²Si,P)-Me₂Si(CH₂)₂PPh₂](PMe₃)₂ and subsequent reductive elimination of methane. X-Ray crystal structure analysis revealed that 2 adopts a slightly distorted square planar geometry. When the reaction of 1 with MeLi was carried out in the presence of PMe₃, a coordinatively saturated silylrhodium(I) complex Rh[(κ²Si,P)-Me₂Si(CH₂)₂PPh₂](PMe₃)₃ (3) was formed. According to the X-ray crystal structure analysis, 3 adopts a five-coordinate, slightly distorted trigonal-bipyramidal arrangement in which the silyl silicon atom and a PMe₃ ligand occupy the axial positions. Variable temperature NMR measurements revealed that both 2 and 3 undergo the exchange of PMe₃ ligands on the NMR timescale. The exchange in 2 is intramolecular, while that in 3 is intermolecular. Treatment of HSiMe₂Ph with 2 gave rise to selective dehydrogenative coupling of hydrosilanes to afford (SiMe₂Ph)₂ and RhH₂[(κ²Si,P)-Me₂SiCH₂CH₂PPh₂](PMe₃)₂ (5).