Chemocatalytic Conversion of Dinitrogen to Ammonia Mediated by a Tungsten Complex.

Whereas molybdenum dinitrogen complexes have played a major role as catalytic model systems of nitrogenase, corresponding tungsten complexes were in most cases found to be catalytically inactive. Herein, we present a modified pentadentate tetrapodal (pentaPod) phosphine ligand in which two dimethylphosphine groups of the pentaPod (P5) ligand have been replaced with phospholanes (Pln). The derived molybdenum complex [Mo(N)P5] generates 22 and the analogous tungsten complex [W(N)P5] 7 equivalents of NH from N in the presence of 180 equivalents of SmI(THF)/HO, rendering the latter the first tungsten complex chemocatalytically converting N to NH. In contrast, the tungsten complex [W(N)P5] generates ammonia from N only in a slightly overstoichiometric fashion. The reasons for these reactivity differences are investigated with the help of spectroscopic and electrochemical methods.