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*(iPr3P)OsBr (2) with SiH4 and primary and secondary hydrosilanes were examined. Compared to the previously studied ruthenium complex Cp(iPr3P)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*(iPr3P)(H)2OsSiRR'][B(C6F5)4] (R = aryl, silyl; R' = aryl, H). The silylene complexes exhibit downfield 29Si chemical shifts ranging from 316 ppm (R = 2,4,6-iPr3C6H2, 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*(iPr3P)Os(H)(Br)SiH2SiPh3 (11) with LiB(C6F5)4 provided the unexpected rearrangement product [Cp*(iPr3P)(H)2OsSi(Ph)SiPh2H][B(C6F5)4] (22). Reaction of 2 with KB(C6F5)4 produced the metalated complex {Cp*[iPr2P(η2-MeCCH2)]OsH2}[B(C6F5)4] (24), which was shown to act as a synthon for the 14-electron species Cp*(iPr3P)Os+. Thus, 24 reacted with Ph2SiH2 to afford [Cp*(iPr3P)(H)2OsSiPh2][B(C6F5)4] (14).