Facile, Reversible Hydrogen Activation by Low-Coordinate Magnesium Oxide Complexes.

New approaches to achieve facile and reversible dihydrogen activation are of importance for synthesis, catalysis, and hydrogen storage. Here we show that low-coordinate magnesium oxide complexes [{(nacnac)Mg}(μ-O)] , with nacnac = HC(RCNDip), Dip = 2,6-PrCH, R = Me (), Et (), Pr (), readily react with dihydrogen under mild conditions to afford mixed hydride-hydroxide complexes [{(nacnac)Mg}(μ-H)(μ-OH)] . Dehydrogenation of complexes is strongly dependent on remote ligand substitution and can be achieved by simple vacuum-degassing of (R = Pr) to regain . Donor addition to complexes also releases hydrogen and affords donor adducts of magnesium oxide complexes. Computational studies suggest that the hydrogen activation mechanism involves nucleophilic attack of an oxide lone pair at a weakly bound H···Mg complex in an S2-like manner that induces a heterolytic dihydrogen cleavage to yield an MgOH and an MgH unit. Alternative synthetic routes into complex from a magnesium hydride complex have been investigated and the ability of complexes or to act as catalysts for the hydrogenation of 1,1-diphenylethene (DPE) has been tested.