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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.

CpCr(N0)2(N02) exists as a mixture of the nitro and nitrito linkage isomers, with the nitrito isomer predominating in both solution and the solid state (Cp = rj5-C5H5). The Cr-N02 ** Cr-ONO equilibrium is markedly solvent and temperature dependent: in CDC13, AH^= 1.8(3) kcal/mol and £«, = 9.3(9) eu. The treatment of CpCr(N0)2(N02) with Na15N02 in MeOH leads to the exchange of free and bound N02~, eventually giving a statistical distribution of the 15N label in the NO and N02 ligands and free N02" at equilibrium. The linkage isomers of the labeled CpCr(N0)2(15N02) complex convert to a statistical mixture of the CpCr(15NO)(NO)(N02) and CpCr(15NO)(NO)(ONO) isotopomers in solution and in the solid state. The initial disappearance rate of the CpCr(NO)2(15N02) isotopomer is first-order, leading to AH* = 11.3(6) kcál/mol and AS* = 10(2) eu in MeOH and AH* = 14(1) kcal/mol and AS* = 20(1) eu in toluene. This behavior, together with the fact that CpCr-(N0)2(i5N02) equilibrates to CpCr(l5N0)(N0)(N02) in the solid state, supports an intramolecular O atom transfer process between «'¿-coordinated NO and N02 ligands.

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The paramagnetic hydride complexes, (dmpe),MCI,H, [ M = Nb, Ta; dmpe = 1,2-bis(dimethylphosphino)ethane] have been isolated from the reactions of (dmpe),MCI, with molecular hydrogen and characterized by magnetic susceptibility measurements, i.r. and e.s.r. spectroscopy, and for the case where M = Ta, by X-ray crystal lograp hy.