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^•). 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).