Electrochemical generation of low-valent molybdenum tri-tertiary phosphine complexes: interactions with monophosphines and molecular nitrogen

Abstract

The electrochemical reduction of the 15-electron molybdenum(III) complex [MoCl₃(dpepp)], dpepp = Ph₂PCH₂CH₂P(Ph)CH₂CH₂PPh₂, has been studied in the presence of PPh₃ under argon and under molecular nitrogen. The primary reduction of the trichloride involves a reversible single-electron transfer to give the unstable 16-electron molybdenum(II) anion [MoCl₃(dpepp)]^–. Loss of chloride from this anion prior to or following further electron transfer provides two principal pathways to molybdenum(0) products, [Mo(η⁶-C₆H₅PPh₂)(dpepp)] under Ar or cis-[Mo(N₂)₂(dpepp)(PPh₃)] under molecular nitrogen, a relatively high potential pathway via molybdenum(I) solvated intermediates and a low potential pathway via trans-[MoCl₂(dpepp)(PPh₃)]. The cis-dinitrogen complex is unstable on the preparative time-scale, small amounts of trans-[Mo(N₂)₂(dpepp)(PPh₃] are formed, presumably by isomerisation, but the major product is the η⁶-arene complex.