Synthesis and characterization of five-coordinate, 16-electron RuII complexes supported by tridentate bis(phosphino)silyl ligation

Abstract

The synthesis of 16-electron complexes of the type (Cy-PSiP)RuX(L) (Cy-PSiP = κ³-(2-Cy₂PC₆H₄)₂SiMe) is reported. Treatment of (Cy-PSiP)H with one equiv. RuCl₂(PPh₃)₃ in the presence of Et₃N afforded a mixture of (Cy-PSiP)RuCl(PPh₃) (1) and [(Cy-PSiP)RuCl]₂ (2), which exists in a temperature-dependent equilibrium process involving reversible dissociation of PPh₃ from 1 to form 2. While treatment of this equilibrium mixture with PMe₃ afforded (Cy-PSiP)RuCl(PMe₃) (3) cleanly, this product was more straightforwardly prepared by the addition of PMe₃ to 2 (97% yield). Attempts to form an alkyl complex of the type (Cy-PSiP)RuMe(PMe₃) via treatment of 3 with MeMgBr led to the dehydrogenation and cyclometalation of a cyclohexyl phosphino group to give the isolable 18-electron complex [MeSi(C₆H₄PCy₂)(C₆H₄PCy(η³-C₆H₈))]RuPMe₃ (4, 78% yield). The hydrido complex (Cy-PSiP)RuH(PMe₃) (5) was identified as a minor by-product in this dehydrogenative process. Whereas simple 16-electron alkyl complexes of the type (Cy-PSiP)RuR(PMe₃) remained elusive, the isolable allyl complex (Cy-PSiP)Ru(η³-C₃H₅) (9) was successfully prepared from 2 and (C₃H₅)MgCl (79% yield). Treatment of 3 with Me₃SiN₃ or NaN₃ did not generate a five-coordinate azido species. However, the putative dinuclear complex [(Cy-PSiP)RuN₃]₂ (10) was observed to react with one equiv. of PMe₃ to afford the isolable five-coordinate azido complex (Cy-PSiP)Ru(N₃)(PMe₃) (11; 94% yield). Crystallographic data for 3, 4, 5, 9 and 11 are presented.