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

With [Mo(N2)(P2MePP2Ph)] the first Chatt‐type complex with one coordination site catalytically converting N2 to ammonia is presented. Employing SmI2 as reductant and H2O as proton source 26 equivalents of ammonia are generated. Analogous Mo0‐N2 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 N2 and the unique topology of the pentadentate tetrapodal (pentaPod) ligand P2MePP2Ph. The analogous hydrazido(2‐) complex [Mo(NNH2)(P2MePP2Ph)](BArF)2 is generated by protonation with HBArF 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. [Mo(N2)(P2MePP2Ph)] is the first Chatt‐type complex with one coordination site that catalytically converts N2 to ammonia (26 equivalents). The fact that the analogous hydrazido(2‐) complex is catalytically active as well demonstrates that the corresponding catalytic cycle follows a mononuclear pathway. Proton and electron transfer to N2 are mediated by the PCET reagent SmI2/H2O.