Alkene epoxidations catalysed by molybdenum(VI) supported on imidazole-containing polymers. Part 3. Epoxidation of oct-1-ene and propene

Abstract

Six polymer-supported Mo^VI catalysts have been prepared. Two involve supported aminomethyl-2-pyridine (AMP) ligands, and the other four various ligands based on imidazole. All catalysts are active in the epoxidation of propene using tert-butyl hydroperoxide in the liquid state at 80 °C and at a pressure of 400 psi (He). The catalysts with AMP ligands show a slight fall in activity on recycling, but this trend is also accompanied by significant and continuing leaching of Mo. In contrast the catalysts based on imidazole-containing polymers generally show better retention of catalyst activity, and most importantly no measurable loss of Mo after the first few cycles. The best species is based on polybenzimidazole, PBI. This shows only modest activity when used initially but when the catalyst is recycled the conversion in the reaction rises to 99.8% and the selectivity is essentially 100%. Thermogravimetric analysis also shows that this polymer-supported catalyst is stable in air to ca. 400 °C, and so also offers the possibility of application under even more extreme oxidative conditions than those used to date.