Nanoparticles of palladium supported on bacterial biomass : new re-usable heterogeneous catalyst with comparable activity to homogeneous colloidal Pd in the Heck reaction

The Heck coupling of iodobenzene with ethyl acrylate or styrene was used to assess the catalytic properties of biogenic nanoparticles of palladium supported upon the surface of bacterial biomass (bioPd), this approach combining advantages of both homogeneous and heterogeneous catalysts. The biomaterial was comparably active or superior to colloidal Pd in the Heck reaction, giving a final conversion of 85% halide and initial rate of 0.17 mmol/min for the coupling of styrene and iodobenzene compared to a final conversion of 70% and initial rate of 0.15 mmol/min for a colloidal Pd catalyst under the same reaction conditions at 0.5 mol.% catalyst loading. It was easily separated from the products under gravity or by filtration for reuse with low loss or agglomeration. When compared to two alternative palladium catalysts, commercial 5% Pd/C and tetraalkylammonium-stabilised palladium clusters, the bioPd was successfully reused in six sequential alkylations with only slight decreases in the rate of reaction as compared to virgin catalyst (initial rate normalised for g Pd decreased by 5% by the 6th run with bioPd catalyst cf. a decrease of 95% for Pd/C). A re-usable Pd-catalyst made cheaply from bacteria left over from other processes would impact on both conservation of primary sources via reduced metal losses in industrial application and the large environmental demand of primary processing from ores.