Bimetallic Cooperative Cleavage of Dinitrogen to Nitride and Tandem Frustrated Lewis Pair Hydrogenation to Ammonia

Abstract

Although reductive cleavage of dinitrogen (N2) to nitride (N3−) and hydrogenation with dihydrogen (H2) to yield ammonia (NH3) is accomplished in heterogeneous Haber–Bosch industrial processes on a vast scale, sequentially coupling these elementary reactions together with a single metal complex remains a major challenge for homogeneous molecular complexes. Herein, we report that the reaction of a chloro titanium triamidoamine complex with magnesium effects complete reductive cleavage of N2 to give a dinitride dititanium dimagnesium ditriamidoamine complex. Tandem H2 splitting by a phosphine–borane frustrated Lewis pair (FLP) shuttles H atoms to the N3−, evolving NH3. Isotope labelling experiments confirmed N2 and H2 fixation. Though not yet catalytic, these results give unprecedented insight into coupling N2 and H2 cleavage and N−H bond formation steps together, highlight the importance of heterobimetallic cooperativity in N2 activation, and establish FLPs in NH3 synthesis.

Terminal uranium(V)-nitride hydrogenations involving direct addition or Frustrated Lewis Pair mechanisms

“…One solution to overcome this hydrogenolysis challenge may be to exploit Frustrated Lewis Pair (FLP) chemistry 13,14 , but so far this has been focussed on M-N 2 complexes 15,16 . Usually with mid-or latetransition metals 3 , most metal-nitride hydrogenations involve sequential protonations [17][18][19][20][21][22] , but bridging nitrides in poly-iron/titanium/-zirconium complexes have been reported to react with H 2 to give imido-hydride and NH 3 products [23][24][25] . Only three terminal metal-nitrides have been reported to undergo hydrogenolysis with H 2 .…”