Mesoporous SBA-15 modified with manganese pyrazolylpyridine complexes for the catalytic epoxidation of terminal alkenes

A manganese-based hybrid mesoporous material (denoted as 5) was synthesized by covalent grafting of [MnII(1)2](OAc)2 (3) (1 = [3-(2-pyridyl)pyrazol-1-yl]acetic acid amide) onto the surface of SBA-15, and characterized by means of XRD, N2 adsorption–desorption, FT-IR, Raman, EPR and UV–vis spectroscopic techniques. Catalytic tests showed that 5 could act as an efficient heterogeneous catalyst for the epoxidation of a wide range of alkenes (including terminal ones) under mild reaction conditions when peracids (e.g., meta-chloroperbenzoic acid) are used as oxidants. Moreover, the catalytic performance of 5 is solvent-dependent, it exhibits higher catalytic activity and selectivity to epoxides when the reaction is carried out in aprotic solvent like CH3CN. UV–vis and electrochemical measurements revealed that high-valent Mn species are easily formed during the reaction course, when meta-chloroperbenzoic acid is used as oxidant and CH3CN is used as solvent, being probably the main reason for the high activity of 5 and its selectivity toward epoxide formation.

Mesoporous SBA-15 materials modified with manganese pyrazolylpyridine complexes is an efficient heterogeneous catalyst for the epoxidation of alkenes (including terminal alkenes) with m-CPBA as oxidant under mild conditions. UV–vis measurements results revealed that high-valent Mn species are easily formed when CH3CN is used as solvent, should be the main active intermediates for the epoxidation reaction.Figure optionsDownload high-quality image (126 K)Download as PowerPoint slideHighlights
► Manganese pyrazolylpyridine complexes modified SBA-15 (5) is prepared.
► 5 is active and stable heterogeneous catalyst for the epoxidation of terminal alkenes.
► OMnIV-species should be the main active intermediates for the epoxidation reaction.