Heptacoordinate tricarbonyl Mo(II) complexes as highly selective oxidation homogeneous and heterogeneous catalysts

摘要

[MoX2(CO)3(pyca)] (X = I,Br) complexes bearing the ligand C5H4NCH=N(CH2)2CH3 (pyca,2) were prepared and characterized by elemental analysis as well as FTIR and 1H and 13C solution NMR spectroscopy.Using the modified ligand C5H4NCH=N(CH2)3Si(OEt)3 (pycaSi,3),they were immobilized in MCM-41 (MCM) and in mesoporous materials (i.e.,periodic mesoporous organosilica [PMO]) and then characterized by powder X-ray diffraction,N2 adsorption analysis,FTIR,and 29Si MAS and CP MAS and 13C CP MAS solid-state NMR spectroscopy.These new materials and complexes were tested in the oxidation of cyclohexene,cyclooctene,and styrene and in the polymerization of styrene and norbornene.All were good catalyst precursors for olefin epoxidation with TBHP (t-butylhydroperoxide),leading selectively to epoxides with high conversions and TOFs and achieving high conversions in the second run.This finding,combined with the fact that the materials outperformed the homogeneous complexes,make these catalysts very attractive.They combine the selectivity and activity of the homogeneous species with the features of materials.The iodine-containing materials performed better for styrene (100% conversion),and the bromine-containing materials displayed higher conversion for cyclooctene.