Synthesis of hydride and alkyl compounds containing the Cp*Os(NO) fragment. Crystal structure of [Cp*Os(mu-NO)](2)

Treatment of the pentamethylcyclopentadienyl (Cp*) compound Cp*Os(NO)Br-2 ( 1) with NaBH4 yields the dihydride Cp*Os(NO)Hz. The dihydride loses Hz over several days in solution to form [Cp*Os(mu-NO)](2); this dinuclear compoun d can also be formed directly by reduction of 1 with zinc powder. The X-ray crystal structure of [Cp*Os(mu-NO)](2) shows that nitrosyl ligands are bri dging and that the Os-Os distance is 2.539(1) Angstrom. Compound 1 reacts w ith MgR2 to form the monoalkylated products Cp*Os(NO)RBr, where R = Me, CH2 SiMe3, Ph, or o-Tol. The slow ligand substitution kinetics of this reaction prevent the formation of dialkyls of stoichiometry Cp*Os(NO)R-2, even afte r long reaction times or when a large excess of alkylating agent is used. D ialkyls such as Cp*Os(NO)Me-2 can, however, be obtained by treatment of Cp* Os(NO)MeBr with silver trifluoromethanesulfonate followed by addition of di methylmagnesium.