A Chatt-Type Catalyst with One Coordination Site for Dinitrogen Reduction to Ammonia.

With [Mo(N )(P PP )] the first Chatt-type complex with one coordination site catalytically converting N to ammonia is presented. Employing SmI as reductant and H O as proton source 26 equivalents of ammonia are generated. Analogous Mo -N complexes supported by a combination of bi- and tridentate phosphine ligands are catalytically inactive under the same conditions. These findings are interpreted by analyzing structural and spectroscopic features of the employed systems, leading to the conclusion that the catalytic activity of the title complex is due to the strong activation of N and the unique topology of the pentadentate tetrapodal (pentaPod) ligand P PP . The analogous hydrazido(2-) complex [Mo(NNH )(P PP )](BAr ) is generated by protonation with HBAr in ether and characterized by NMR and vibrational spectroscopy. Importantly, it is shown to be catalytically active as well. Along with the fact that the structure of the title complex precludes dimerization this demonstrates that the corresponding catalytic cycle follows a mononuclear pathway. The implications of a PCET mechanism on this reactive scheme are considered.