Catalytic Alkyne Semihydrogenation with Polyhydride Ni/Ga Clusters.

The bimetallic, deca-nuclear Ni3Ga7-cluster of the formula [Ni3(GaTMP)3(µ2-GaTMP)3(µ3-GaTMP)] (1, TMP = 2,2,6,6-tetramethylpiperidinyl) reacts reversibly with dihydrogen under the formation of a series of (poly-)hydride clusters 2. Low-temperature 2D NMR experiments at -80 °C show that 2 consist of a mixture of a di- (2Di), tetra- (2Tetra) and hexahydride species (2Hexa). The structures of 2Di and 2Tetra are assessed by a combination of 2D NMR spectroscopy and DFT calculations. The cooperation of both metals is essential for the high hydrogen uptake of the cluster. Polyhydrides 2 are catalytically active in the semihydrogenation of 4-octyne to 4-octene with good selectivity. The example is the first of its kind and conceptually relates properties of molecular, atom-precise transition metal / main group metal clusters to the respective solid-state phase in catalysis.