Electrochemical Acetonitrile Release from Dinitrogen-Derived Rhenium Imido Complexes through Proton-Coupled Electron Transfer

The oxidation of rhenium(III) azavinylidene complexes that originate from the reductive splitting of dinitrogen enables the stepwise conversion of N2 to nitriles. We here report the development of an electrochemical protocol and the experimental and computational examination of the reaction mechanism. Electrolysis of N2-derived {ReIII–N═CHCH3} azavinylidene complexes in the presence of chloride and NEt3 affords MeCN nearly quantitatively and the respective ReIV 3-electron oxidation products in yields around 50%. The lower yields in the Re product can be attributed to degradation processes of the supporting pincer ligands. The first oxidation is coupled to chloride addition. Subsequent proton-coupled electron transfer (PCET) affords the nitrile product as a net 2-electron oxidation of the nitrogenous ligand. The overoxidation to rhenium(IV) originates in a large potential inversion upon restoration of rhenium(III) as an inherent feature to the mechanism.