Selective propylene dimerization to 2,3-dimethylbutenes by heterogenized polymer-supported β-dithioacetylacetonate nickel(II) precursors activated by organoaluminium co-catalysts

Abstract

Heterogenized nickel catalysts, prepared in situ by anchoring nickel(II) phosphino complexes to polymer-bound β-dithioacetylacetonate (sacsac) chelate ligands and activated by organoaluminium co-catalysts, have been employed for the selective propylene oligomerization to 2,3-dimethylbutenes (DMB). In particular, the effect of reaction conditions as well as of nature of phosphine ligand and organoaluminium activator was studied. The obtained data have shown that the above catalysts, at temperatures below 0°C and in the presence of chlorobenzene as reaction medium, display a very high activity and selectivity to DMB, when basic and bulky alkyl phosphine ligands and organoaluminium co-catalysts of medium Lewis acidity are used. The performances given above are very similar to those obtained with the corresponding homogeneous catalysts. Flow experiments have allowed to check that the heterogenized catalysts given above are substantially stable, maintaining their performances during the time. No significant metal leaching was detected in the course of the reaction, at least under the adopted conditions, thus suggesting that these polymer-supported nickel catalysts behave as really heterogeneous catalysts, due to the presence of the bidentate sacsac ligand able to permanently fix the metal to the resin.