Syntheses and applications of functionalized polyolefins as ligands for homogeneous transition metal catalysts

Abstract

Ethylene oligomers having diphenylphosphine, diaryl and triaryl phosphite functional groups were used as supports for hydrogenation, hydroformylation and diene cyclooligomerization catalysts. An advantage of these ethylene oligomer-ligated catalyst was their solubility in common hydrocarbon solvents such as toluene at 95 °C and quantitative separation as a precipitate on cooling these solutions to 25 °C. Various alkenes were hydrogenated using analogs of Wilkinson's catalyst and these were also used to hydroformylate 1-hexene and styrene homogeneously at 100 °C in xylene and toluene. The hydrogenation and hydroformylation rates were comparable to those seen using homogeneous catalysts and were an order of magnitude higher than seen using cross-linked polystyrene-supported catalysts. The substrate size was not a significant factor affecting the hydrogenation rates because of the homogeneity of the catalyst. This differs from the effect seen in the case of cross-linked polymer-supported catalysts. The homogeneity of the catalytic species involved in these reactions was established through a "triphase test" where a 1% DVB cross-linked polystyrene bearing styrene units was hydrogenated or hydroformylated. A simultaneous catalytic reduction/stoichiometric oxidation of unsaturated alcohols was affected using a hydrogenation catalyst and a poly(vinyl pyridinium)-Cr(VI) oxidant. This reaction shows that a macromolecular matrix and oligomeric ligands can kinetically isolate two mutually incompatible species. An additional advantage of using ethylene oligomer-ligated catalyst in this case is the facile recovery of each individual catalyst, reagent and product. Polyethyl diaryl phosphites and polyethylphenyl diaryl phosphites were used to ligate Ni(0) catalysts and to carry out cyclooligomerizations of butadiene homogeneously at 100 °C in toluene. The catalytic activity and product selectivity for 1,5-cyclooctadiene were similar to that obtained using conventional homogeneous catalysts. The active nickel catalyst was separable as a precipitate in polyethylene by cooling the hot solution. The recovered oligomerligated catalyst was reused in cyclodimerization reactions without reactivation of the catalyst. The highest selectivity for COD was seen when the nickel to phosphite functionalized oligomeric-ligand ratio was 1:1.