Molecular systems, including homogeneous transition metals complexes and those of main group elements, are examined to illustrate the various types of stoichiometric N−H bond cleavage reactions. Molecular complexes that mediate catalytic NH3 oxidation to N2 through chemically or electrochemically driven reactions are described.
Abstract
The molecular complexes described herein use main-group elements or transition metals to control the stoichiometric cleavage of N−H bonds of ammonia (NH3) and/or catalyze chemical and electrochemical NH3 oxidation to dinitrogen (N2). We highlight the phenomenon of coordination-induced bond weakening and a variety of N−H bond cleavage mechanisms of NH3 including H atom abstraction, inter- and intra-molecular deprotonation reactions, oxidative addition, and σ -bond metathesis that have been demonstrated with molecular systems. We provide an overview of the molecular complexes reported for the rapidly developing field of NH3 oxidation catalysis to form N2. These systems exhibit several diverse structure types and innovative ligands to support transition metals capable of activating NH3 and mediating a challenging chemical transformation that requires breaking strong N−H bonds and forming an N−N bond en route to N2 formation.