Synthetic Nitrogen Fixation with Mononuclear Molybdenum(0) Phosphine Complexes: Occupying the trans-Position of Coordinated N2

Abstract

Synthetic nitrogen fixation with molybdenum phosphine complexes has witnessed a renaissance recently due to the discovery that such systems are competent to catalytically convert N2 to ammonia. In the framework of this research area, we have prepared complexes of the type [Mo(N2)(PEP)(P2)] (E = N, P; P2 = dppm, dmpm) in which the linear PEP ligand coordinates in a facial geometry. Similar complexes have been prepared using mixed carbene–phosphine (PCP) ligands. Furthermore, molybdenum bis(dinitrogen) complexes have been synthesized which are facially coordinated by a tripod ligand and contain the bidentate coligands dppm and dmpm. Recently, both of these approaches have been united in the synthesis of a Mo(0)–N2 complex supported by a pentadentate tetrapodal (pentaPod) ligand. The structural, electronic, and vibrational properties of all of these dinitrogen complexes have been investigated by NMR, IR, and Raman spectroscopy, and their reactivities in a nitrogen fixing cycle have been evaluated. To this end, protonated derivatives have been investigated as well. On the basis of these results and DFT calculations, these systems are promising candidates for the catalytic conversion of N2 to ammonia.