Copper-complexed dipyridyl-pyridazine functionalized periodic mesoporous organosilica as heterogeneous catalyst for styrene epoxidation

Abstract

A new heterogenous catalyst has been synthesized by immobilization of a copper complex on dipyridyl-pyridazine functionalized periodic mesoporous organosilica (dppz-vPMO). This ordered support was firstly prepared by a co-condensation reaction between vinyltriethoxysilane and 1,2-bis(trimethoxysilyl)ethane and further post-functionalized through a hetero Diels-Alder reaction with 3,6-di-2-pyridyl-1,2,4,5-tetrazine. Techniques such as XRD, N2 isotherms, TEM, 13C NMR, XPS and DRIFT, among others, were employed to characterize the surface functionalized materials. These results have proven the ordered mesostructure of the materials as well as the presence of novel nitrogen-chelating heterocyclic compounds in the pore surface after the post-modification process. Additionally, it has been confirmed the successful anchoring of a copper complex on the dipyridyl-pyridazine (dppz) ligands. The resulting material was evaluated as heterogenous catalyst in the epoxidation of styrene using tert-butylhydroperoxide (TBHP) as oxidant. Under optimized reaction conditions, Cu@dppz-vPMO showed a high styrene conversion (86.0 %) and a remarkable selectivity to styrene oxide (41.9 %). Indeed, this catalyst provided excellent catalytic results in terms of stability, reaction rate, conversion and selectivity compared to other bipyridine-like copper catalysts.