Thermoneutral N−H Bond Activation of Ammonia by a Geometrically Constrained Phosphine

A geometrically constrained phosphine bearing a tridentate NNS pincer ligand is reported. The effect of the geometric constraint on the electronic structure was probed by theoretical calculations and derivatization reactions. Reactions with N−H bonds result in formation of cooperative addition products. The thermochemistry of these transformations is strongly dependent on the substrate, with ammonia activation being thermoneutral. This represents the first example of a molecular compound that reversibly activates ammonia via N−H bond scission in solution upon mild heating. A geometrically constrained phosphine bearing an NNS pincer ligand is reported. The steric and electronic parameters were tuned to allow for unprecedented reversible ammonia activation via N−H bond scission. The phosphine's electronic structure and the associated reaction mechanism of N−H bond scission are elucidated by derivatization reactions and computational methods.