Combined KH/alkaline-earth metal amide catalysts for hydrogenation of alkenes†
Using earth abundant and environmentally friendly base metal catalysts instead of noble transition metal catalysts is becoming a hot topic in catalytic hydrogenation reactions. Under this guidance, several soluble, structurally well-defined alkaline-earth metal hydride complexes were reported to catalyze hydrogenation reactions. The easily available alkali metal hydrides, however, showed poor activity probably because of their saline structures and high lattice energies. Herein, we reported the efficient hydrogenation of various styrenes and α-alkenes with the combined catalysts of KH and Ca(HMDS)2·(THF)2 or Mg(HMDS)2·Et2O (HMDS = −N(SiMe3)2). The combined catalysts exhibited much better activity than their components KH or alkaline-earth metal amides, suggesting an obvious bimetallic synergistic effect. Preliminary mechanism studies revealed a degradation and activation effect of the alkaline-earth metal amides on saline KH.