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

Treatment of the pentamethylcyclopentadienyl (Cp*) compound Cp*Os(NO)Br<sub>2</sub> (<b>1</b>) with NaBH<sub>4</sub> yields the dihydride Cp*Os(NO)H<sub>2</sub>. The dihydride loses H<sub>2</sub> over several days in solution to form [Cp*Os(μ-NO)]<sub>2</sub>; this dinuclear compound can also be formed directly by reduction of <b>1</b> with zinc powder. The X-ray crystal structure of [Cp*Os(μ-NO)]<sub>2</sub> shows that nitrosyl ligands are bridging and that the Os−Os distance is 2.539(1) Å. Compound <b>1</b> reacts with MgR<sub>2</sub> to form the monoalkylated products Cp*Os(NO)RBr, where R = Me, CH<sub>2</sub>SiMe<sub>3</sub>, Ph, or <i>o</i>-Tol. The slow ligand substitution kinetics of this reaction prevent the formation of dialkyls of stoichiometry Cp*Os(NO)R<sub>2</sub>, even after long reaction times or when a large excess of alkylating agent is used. Dialkyls such as Cp*Os(NO)Me<sub>2</sub> can, however, be obtained by treatment of Cp*Os(NO)MeBr with silver trifluoromethanesulfonate followed by addition of dimethylmagnesium.