Catalytic Alkyne Semihydrogenation with Polyhydride Ni/Ga Clusters
Abstract
The bimetallic, decanuclear Ni$_3$Ga$_7$-cluster of the formula [Ni$_3$(GaTMP)$_3$(µ$^2$-GaTMP)$_3$(and µ$^3$-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 and DEG;C show that 2 consist of a mixture of a di- (2$_{Di}$), tetra-(2$_{Tetra}$) and hexahydride species (2$_{Hexa}$). The structures of 2$_{Di}$ and 2$_{Tetra}$ 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.
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