Synthesis of Hydride and Alkyl Compounds Containing the Cp*Os(NO) Fragment. Crystal Structure of [Cp*Os(μ-NO)]₂

Treatment of the pentamethylcyclopentadienyl (Cp*) compound Cp*Os(NO)Br₂ (1) with NaBH₄ yields the dihydride Cp*Os(NO)H₂. The dihydride loses H₂ over several days in solution to form [Cp*Os(μ-NO)]₂; this dinuclear compound can also be formed directly by reduction of 1 with zinc powder. The X-ray crystal structure of [Cp*Os(μ-NO)]₂ shows that nitrosyl ligands are bridging and that the Os−Os distance is 2.539(1) Å. Compound 1 reacts with MgR₂ to form the monoalkylated products Cp*Os(NO)RBr, where R = Me, CH₂SiMe₃, Ph, or o-Tol. The slow ligand substitution kinetics of this reaction prevent the formation of dialkyls of stoichiometry Cp*Os(NO)R₂, even after long reaction times or when a large excess of alkylating agent is used. Dialkyls such as Cp*Os(NO)Me₂ can, however, be obtained by treatment of Cp*Os(NO)MeBr with silver trifluoromethanesulfonate followed by addition of dimethylmagnesium.