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Synthesis and Structure of CpMo(CO)(dppe)H and Its Oxidation by Ph3C+

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journal contribution
posted on 12.06.2006, 00:00 by Tan-Yun Cheng, David J. Szalda, Jie Zhang, R. Morris Bullock
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). The proposed mechanism involves one-electron oxidation of CpMo(CO)(dppe)H by Ph3C+ to give the radical-cation complex [CpMo(CO)(dppe)H]•+. Proton transfer from [CpMo(CO)(dppe)H]•+ to CpMo(CO)(dppe)H, loss of dihydrogen from [CpMo(CO)(dppe)(H)2]+, and oxidation of Cp(CO)(dppe)Mo 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]•+ 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).