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 NH 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.