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 penta methylcyclopentadienyl(phosphine) ligand sets are described. The osmiu m silyl complexes are prepared by thermal reactions of hydrosilanes wi th osmium(II) alkyl complexes of the type Cp'(PR3)(2)OsCH2SiMe3 (Cp' = Cp, R = Ph (4), Me (5); Cp' = eta(5)-C5Me5, R = Me (7)), which in tur n are available via alkylation of the corresponding bromo complexes. T he synthesis of alkyl derivatives of Cp(PR3)(2)Os (R = Ph, Me) require s the use of dialkylmagnesium reagents, while alkylation of the more e lectron-rich Cp-(PMe3)(2)Os system can be achieved using Grignard rea gents. Additionally, reaction of Cp(PPh3)(2)OsBr with AgOTf (Tf = SO2C F3) affords the osmium(II) triflate complex Cp(PPh3)(2)OsOTf (2), whic h possesses a labile triflate group. The structure of complex 2 was de termined 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) provid es metallacycle complexes of the type Cp-(PMe3)(H)Os[C6H3(3-Me)(6-S)S iR2] (R = 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, dependi ng on the reaction conditions and the strength of the Os-P bond. React ion of 7 with HSiMeCl2 or HSiCl3 affords, exclusively, the osmium(II) silyl derivatives. Exchange reactions at silicon are used to synthesiz e Cp-(PMe3)(2)OsSiMe2OTf (24) and Cp-*(PMe3)(2)OsSiMe[S(p-Tol)](2) (2 5) from the corresponding chloro(silyl) complexes Cp-(PMe3)(2)OsSiMe2 Cl (17) and Cp-(PMe3)(2)OsSiMeCl2 (18). The solution behavior and sol id-state structure of 24 indicate that the compound may be described a s a base-stabilized silylene complex.