In the chemist's hands, dinitrogen (N2) is quite unreactive under mild conditions, yet the metalloenzyme nitrogenase manages to convert N2 to NH3. Previously, Fryzuk et al. have reported on a ditantalum complex produced when N2 displaced two of the four hydrides bridging the two Ta centers, accompanied by a reductive elimination of H2; the dinitrogen molecule adopted a side-on binding configuration at one Ta atom and end-on at the other. Now they report density functional calculations and reactivity studies. The lack of d-bonding in the side-on bond suggests that this binding configuration is enforced mainly by the geometry of the remaining bridging hydrides. Reaction of the complex with propene leads to insertion of the propene into the hydride bonds and a rearrangement to form a compound in which the Ta centers are now connected by the end-on bonded dinitrogen bridge. Because nitrogenase also appears to eliminate H2 during ammonia synthesis, further studies of these compounds may provide insights into how metal coordination of dinitrogen facilitates biological N2 fixation. -- PDS
J. Am. Chem. Soc., in press.
