Efforts towards novel catalysts for N_2 reduction to NH_3

Abstract

In part as an effort to probe the viability of a single iron site hypothesis for the binding and conversion of N_2 to NH_3 by nitrogenase enzymes, our group has recently reported a tris(phosphine)borane supported mononuclear Fe system that can stabilize many potentially relevant nitrogenous ligands and ligand motifs, such as N_2, N_2H_4, NH_3, NH_2, N_2R_2, N_2R, and NR. This system has also been shown to mediate catalytic conversion of N_2 to NH_3 at low temp. in the presence of strong acid and reductant. More recently we reported a related tris(phosphine)alky supported Fe system that also mediates N_2 to NH_3 conversion under similar conditions. Common features of these systems that may be crit. to the obsd. nitrogen fixation reactivity include local approx. three-fold rotational symmetry at the metal center as well as a flexible axial interaction to a light atom, either carbon or boron. This paper will describe recent efforts to extend this nitrogen fixation catalysis to novel systems and the elucidation of important factors in achieving this reactivity.