Synthesis and structure of CpMo(CO)(dppe)H and its oxidation by Ph3C+

The reaction of CpMo( CO)( dppe) Cl ( dppe) Ph2PCH2CH2PPh2) with Na+[AlH2(OCH2CH2OCH3)(2)](-) gives the molybdenum hydride complex CpMo( CO)( dppe) H, the structure of which was determined by X-ray crystallography. Electrochemical oxidation of CpMo(CO)(dppe) H in CH3CN is quasi-reversible, with the peak potential at - 0.15 V ( vs Fc/Fc(+)). The reaction of CpMo(CO)( dppe) H with 1 equiv of Ph3C+ BF4- in CD3CN gives [CpMo(CO)(dppe)( NCCD3)](+) as the organometallic product, along with dihydrogen and Gomberg's dimer ( which is formed by dimerization of Ph3C center dot). The proposed mechanism involves one-electron oxidation of CpMo( CO)( dppe) H by Ph3C+ to give the radical-cation complex [CpMo(CO)(dppe) H](center dot+). Proton transfer from [CpMo(CO)(dppe)H](center dot+) to CpMo( CO)(dppe) H, loss of dihydrogen from [CpMo(CO)(dppe)(H)(2)](+), and oxidation of Cp(CO)(dppe)Mo-center dot by Ph3C+ lead to the observed products. In the presence of an amine base, the stoichiometry changes, with 2 equiv of Ph3C+ being required for each 1 equiv of CpMo(CO)(dppe) H because of deprotonation of [CpMo(CO)(dppe)H](center dot+) by the amine. Protonation of CpMo(CO)( dppe) H by HOTf provides the dihydride complex [CpMo(CO)(dppe)(H)(2)](+) OTf-, which loses dihydrogen to generate CpMo(CO)(dppe)(OTf).