Calcium Hydride Cation [CaH]+ Stabilized by an NNNN-type Macrocyclic Ligand: A Selective Catalyst for Olefin Hydrogenation.

Reaction of dibenzyl calcium complex [Ca(Me4 TACD)(CH2 Ph)2 ], containing the neutral NNNN-type macrocyclic ligand Me4 TACD (Me4 TACD=1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane), with triphenylsilane gave the cationic dinuclear calcium hydride [Ca2 H2 (Me4 TACD)2 ](PhCHSiPh3 )2 which was characterized by NMR spectroscopy and single-crystal X-ray diffraction. The cation can be regarded as the ligand-stabilized dimeric form of hypothetical [CaH]+ . Hydrogenolysis of benzyl calcium cation [Ca(Me4 TACD)(CH2 Ph)(thf)]+ gave dicationic calcium hydrides [Ca2 H2 (Me4 TACD)2 ][BAr4 ]2 (Ar=C6 H4 -4-t Bu; C6 H3 -3,5-Me2 ) containing weakly coordinating anions. In THF, they catalyzed the isotope exchange of H2 and D2 to give HD and the hydrogenation of unactivated 1-alkenes.