Electrochemistry of molybdenum imides: cleavage of molybdenum–nitrogen triple bonds to release ammonia or amines †

Abstract

The electrochemical reduction of molybdenum(IV) alkylimides trans-[MoX(NR)(dppe)2]+ (X = halide, R = alkyl, dppe = Ph2PCH2CH2PPh2) proceeded by two pathways. In the absence of a source of protons, moderately stable five-co-ordinate molybdenum(II) imides are formed via an initial single-electron transfer followed by rate-determining loss of the trans-halide ligand and an additional electron transfer. In the presence of a source of protons, molybdenum–halide bond cleavage is intercepted by protonation at N which gives an amide intermediate. Further electron-transfer chemistry liberates amines and yields a dinitrogen complex in an overall four-electron process. Molybdenum(IV) imides trans-[MoX(NH)(dppe)2]+ were reduced to amide intermediates with the parent imide cation providing the source of protons and water probably acts as a proton-transfer relay. The amide has two fates; it is either converted into a nitride by hydrogen loss or, at a potential which encompasses its further reduction, yields ammonia and a dinitrogen complex.