Abstract
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(Me) (P5(Me)) ligand have been replaced with phospholanes (Pln). The derived molybdenum complex [Mo(N(2))P5(Pln)] generates 22 and the analogous tungsten complex [W(N(2))P5(Pln)] 7 equivalents of NH(3) from N(2) in the presence of 180 equivalents of SmI(2)(THF)(2)/H(2)O, rendering the latter the first tungsten complex chemocatalytically converting N(2) to NH(3). In contrast, the tungsten complex [W(N(2))P5(Me)] generates ammonia from N(2) only in a slightly overstoichiometric fashion. The reasons for these reactivity differences are investigated with the help of spectroscopic and electrochemical methods.