Structure and Reactivity of (η-C₅R₅)Mo(NO)₂−Halide, −Halomethyl, and −Alkyl Complexes:  Consecutive Aerobic Methylene and Nitrosyl Ligand Oxidation

Cp‘Mo(NO)₂(CH₂X) complexes are isolated in 80−90% yield after the treatment of the Cp‘Mo(NO)₂X complexes in CH₂Cl₂ with ethereal diazomethane in the presence of Cu powder (Cp‘ = η-C₅H₅ (Cp), η-C₅(CH₃)₅ (Cp*); X = Cl, Br). The Cp‘Mo(NO)₂(CH₂I) derivatives are obtained in over 90% yield by treating the Cp‘Mo(NO)₂(CH₂Cl) derivatives with NaI in THF. Four new halomethyl complexes have been characterized by X-ray crystallography and are compared to the related CpMo(NO)₂Br, Cp*Mo(NO)₂Cl, and Cp*Mo(NO)₂(CH₃) derivatives. The structural data and IR data indicate the donor properties of the halomethyl ligands to be intermediate between halide and alkyl ligands. The Cp‘Mo(NO)₂(CH₂X) complexes react initially with O₂ to give CH₂O and the regeneration of the parent Cp‘Mo(NO)₂X complexes. The Cp‘Mo(NO)₂Cl complexes react with O₂ after an induction period to give the well-known Cp‘MoO₂Cl complexes, NO₂, NOCl, and N₂O. Exposure of CpCr(NO)₂(CH(CH₃)Br) to ¹⁸O₂ gives ¹⁸OCH(CH₃) and ¹⁶O-labeled CpCr(NO)₂Br. The Cp‘Mo(NO)₂−alkyl complexes react with O₂ to give the corresponding Cp‘MoO₂−alkyl derivatives in 40−70% yield (alkyl = CH₃, CH₂CH₃). Electrochemical data show the Mo complexes to oxidize at 0.2−0.3 V lower than the Cr congeners.