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

Heterogenized nickel catalysts, prepared in situ by anchoring nickel(II) ph osphino complexes to polymer-bound beta -dithioacetylacetonate (sacsac) che late ligands and activated by organoaluminium co-catalysts, have been emplo yed 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 d ata have shown that the above catalysts, at temperatures below 0 degreesC a nd in the presence of chlorobenzene as reaction medium, display a very high activity and selectivity to DMB, when basic and bulky alkyl phosphine liga nds and organoaluminium co-catalysts of medium Lewis acidity are used. The performances given above are very similar to those obtained with the corres ponding homogeneous catalysts. Flow experiments have allowed to check that the heterogenized catalysts given above are substantially stable, maintaini ng their performances during the time. No significant metal leaching was de tected in the course of the reaction, at least under the adopted conditions , thus suggesting that these polymer-supported nickel catalysts behave as r eally heterogeneous catalysts, due to the presence of the bidentate sacsac ligand able to permanently fix the metal to the resin. (C) 2000 Elsevier Sc ience B.V. All rights reserved.