Early Transition Metal Studies of Dinitrogen Cleavage and Metal-Nitrogen Bond Reactivity Towards Catalytic N2 Fixation

Abstract

The development of energy efficient catalysts that provide a range of commodity chemicals derived from the fixation of N2 is a highly attractive target due to the abundance of molecular nitrogen present in Earth’s atmosphere. Studies have focused on the systematic investigation of several key components of metal-catalyzed N2 fixation that detail molecularly discrete transformations involving the activation of N2, cleavage of the strong N≡N triple bond and N-atom functionalization to provide ammonia and other organic molecules of scientific and industrial interest. To this end, an evaluation of group 5 N2 cleavage using the pentamethylcyclopentadienyl, amidinate (CPAM) ligand framework that includes extensive kinetic and mechanistic investigations detailing the N-N cleavage reaction coordinate has been undertaken. Further studies conducted within group 5 include the synthesis and reactivity of tantalum imido complexes to elucidate metal-nitrogen bond reactivity and N-N cleavage relevant to the Chatt cycle. In group 6, photolytic N-N cleavage has been further investigated. Most notably, chemistry has been discovered for N2-derived metal nitride complexes of Mo and W that gives access to imido complexes capable of participating in nitrene group transfer (NGT) to carbon monoxide and isocyanides to provide isocyanates and carbodiimides respectively. For the first time, it has been demonstrated that imido complexes that participate in NGT chemistry can be derived from N2 to provide N-C based organic products. Collectively, these results serve to establish a new platform for studying the catalytic viability of the discovered transformations.