Synthesis and reactivity of silyl and silylene ligands in the coordination sphere of the 14-electron fragment Cp*(iPr3P)Os+

Oxidative addition reactions of the 16-electron half-sandwich osmium complex Cp*((Pr3P)-Pr-i)OsBr (2) with SiH4 and primary and secondary hydrosilanes were examined. Compared to the previously studied ruthenium complex Cp((Pr3P)-Pr-i)RuCl (1), 2 exhibits a greater tendency to add hydrosilanes to afford stable, isolable silyl complexes. Using an abstraction-migration methodology, in which abstraction of a labile metal halide ligand is followed by 1,2-H migration from silicon to the metal center, new osmium silylene complexes were prepared. Thus, silyl complexes derived from 2 were combined with LiB(C6F5)(4) to afford cationic osmium silylene complexes of the type [Cp*((Pr3P)-Pr-i)(H)(2)Os=SiRR'] [B(C6F5)(4)] (R = aryl, silyl; R' = aryl, H). The silylene complexes exhibit downfield Si-29 chemical shifts ranging from 316 ppm (R = 2,4,6-(Pr3C6H2)-Pr-i, R' = H; 18) to 417 ppm (R = Si(SiMe3)(3), R' = H; 19). Complexes with a hydride substituent at silicon feature downfield shifts for this proton (e.g., 12.06 ppm for 19). The reaction of Cp*((Pr3P)-Pr-i)Os(H)(Br)SiH2SiPh3 (11) with LiB(C6F5)(4) provided the unexpected rearrangement product [Cp*((Pr3P)-Pr-i)(H)(2)Os=Si(Ph)SiPh2H] [B(C6F5)(4)] (22). Reaction of 2 with KB(C6F5)(4) produced the metalated complex {Cp*[(Pr2P)-Pr-i(eta(2)-MeC=CH2)]OsH2} [B(C6F5)(4)] (24), which was shown to act as a synthon for the 14-electron species Cp*((Pr3P)-Pr-i)Os+. Thus, 24 reacted with Ph2SiH2 to afford [Cp*((Pr3P)-Pr-i)(H)(2)Os=SiPh2] [B(C6F5)(4)] (14).