Polyoxoanion- and tetrabutylammonium-stabilized Rh(0)n nanoclusters:: Unprecedented nanocluster catalytic lifetime in solution

The solution catalytic lifetimes of polyoxoanion- and tetrabutylammonium-stabilized Rh(0) nanoclusters have been investigated, including comparison to the lifetimes of [RhCl(PPh3)(3)] (Wilkinson's catalyst), [(1.5-COD)Rh(CH3CN)(2)]BF4, and 5% Rh/Al2O3 under identical conditions. These Rh(0) nanoclusters, derived from the polyoxoanion-supported organometallic precursor [(n-C4H9)(4)N](5)Na-3[(1.5-COD)Rh.P2W15Nb3O62], exhibit catalytic lifetimes that are the longest lifetimes reported for a transition metal nanocluster catalyst in solution, greater than or equal to 193 000 turnovers for olefin hydrogenation. The Rh(0) nanocluster catalytic lifetimes approach those of a solid-oxide-supported heterogeneous Rh(0) catalyst and are an order of magnitude higher than any previously reported for an unsupported nanocluster in solution. The results are of significance in that they provide the catalytic lifetime evidence needed to support the concept of highly stabilized nanocluster catalysts, such as: the present polyoxoanion- and tetrabutylammonium-stabilized nanoclusters, serving as "soluble heterogeneous catalysts".