Theoretical studies of N2 reduction to ammonia in Fe(dmpe)2N2.

Electronic structure calculations using density functional theory were performed on potential intermediates in the reaction of Fe(dmpe)2N2 (dmpe = 1,2-bis(dimethylphosphino)ethane) with protons. Three mechanisms were investigated and compared, and the possibility of a two-electron reduction by a sacrificial Fe(dmpe)2N2 complex was considered in each mechanism. A Chatt-like mechanism, involving the stepwise addition of protons to the terminal nitrogen, was found to be the least favorable. A second pathway involving dimerization of the Fe(dmpe)2N2 complex, followed by the stepwise addition of protons leading to hydrazine, was found to be energetically favorable; however many of the dimeric intermediates prefer to dissociate into monomers. A third mechanism proceeding through diazene and hydrazine intermediates, formed by alternating protonation of each nitrogen atom, was found to be the most energetically favorable.