Synthesis and Reactivity of Silyl and Silylene Ligands in the Coordination Sphere of the 14-Electron Fragment Cp*(ⁱPr₃P)Os⁺

Abstract

Oxidative addition reactions of the 16-electron half-sandwich osmium complex Cp*( i Pr 3 P)OsBr ( 2 ) with SiH 4 and primary and secondary hydrosilanes were examined. Compared to the previously studied ruthenium complex Cp( i Pr 3 P)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(C 6 F 5 ) 4 to afford cationic osmium silylene complexes of the type [Cp*( i Pr 3 P)(H) 2 Os SiRR‘][B(C 6 F 5 ) 4 ] (R = aryl, silyl; R‘ = aryl, H). The silylene complexes exhibit downfield 29 Si chemical shifts ranging from 316 ppm (R = 2,4,6- i Pr 3 C 6 H 2, R‘ = H; 18 ) to 417 ppm (R = Si(SiMe 3 ) 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*( i Pr 3 P)Os(H)(Br)SiH 2 SiPh 3 ( 11 ) with LiB(C 6 F 5 ) 4 provided the unexpected rearrangement product [Cp*( i Pr 3 P)(H) 2 Os Si(Ph)SiPh 2 H][B(C 6 F 5 ) 4 ] ( 22 ). Reaction of 2 with KB(C 6 F 5 ) 4 produced the metalated complex {Cp*[ i Pr 2 P(η 2 -MeC CH 2 )]OsH 2 }[B(C 6 F 5 ) 4 ] ( 24 ), which was shown to act as a synthon for the 14-electron species Cp*( i Pr 3 P)Os + . Thus, 24 reacted with Ph 2 SiH 2 to afford [Cp*( i Pr 3 P)(H) 2 Os SiPh 2 ][B(C 6 F 5 ) 4 ] ( 14 ).