Osmium Alkyl and Silyl Derivatives with Cyclopentadienyl(phosphine) and Pentamethylcyclopentadienyl(phosphine) Ligand Sets

The preparation and characterization of new osmium(II) and osmium(IV) silyl derivatives containing the cyclopentadienyl(phosphine) and pentamethylcyclopentadienyl(phosphine) ligand sets are described. The osmium silyl complexes are prepared by thermal reactions of hydrosilanes with osmium(II) alkyl complexes of the type Cp'(PR3)2OsCH2SiMe3 (Cp' = Cp, R = Ph (4), Me (5); Cp' = η5-C5Me5, R = Me (7)), which in turn are available via alkylation of the corresponding bromo complexes. The synthesis of alkyl derivatives of Cp(PR3)2Os (R = Ph, Me) requires the use of dialkylmagnesium reagents, while alkylation of the more electron-rich Cp*(PMe3)2Os system can be achieved using Grignard reagents. Additionally, reaction of Cp(PPh3)2OsBr with AgOTf (Tf = SO2CF3) affords the osmium(II) triflate complex Cp(PPh3)2OsOTf (2), which possesses a labile triflate group. The structure of complex 2 was determined by X-ray crystallography. Similar to their ruthenium analogs, the osmium(II) alkyl complexes 4, 5, and 7 thermally activate arene C−H bonds. Reaction of 7 with HSiR2[S(p-Tol)] (R = S(p-Tol), Me) provides metallacycle complexes of the = S(p-Tol) (11), Me (13)) via activation of both the Si−H and arene C−H bonds in the silanes. The X-ray structure of 13 is described. Alkyl complexes 4, 5, and 7 react with HSiR2Cl (R = Ph, Me) to give osmium(II) silyl and/or osmium(IV) bis(silyl) hydride species, depending on the reaction conditions and the strength of the Os−P bond. Reaction of 7 with HSiMeCl2 or HSiCl3 affords, exclusively, the osmium(II) silyl derivatives. Exchange reactions at silicon are used to synthesize Cp*(PMe3)2OsSiMe2OTf (24) and Cp*(PMe3)2OsSiMe[S(p-Tol)]2 (25) from the corresponding chloro(silyl) complexes Cp*(PMe3)2OsSiMe2Cl (17) and Cp*(PMe3)2OsSiMeCl2 (18). The solution behavior and solid-state structure of 24 indicate that the compound may be described as a base-stabilized silylene complex.