Encapsulation of chiral Mn(III) salen complexes into aluminium pillared clays: Application as heterogeneous catalysts in the epoxidation of styrene

Two chiral manganese(III) salen complexes bearing different chiral diimine bridges, complexes I and II, were encapsulated into three types of Al-pillared clays (Al-PILCs) by in situ generation of the complexes inside the PILCs; one of the PILCs used was derived from a Wyoming clay (Al-WYO) and the other two were from the same original clay Benavila: (i) Al-BEN, where no surfactant was used in the preparation and (ii) Al-TERG, where a polyalchol, i.e. tergitol was used as surfactant to act as an interlayer gallery template. The Al-pillared clay based materials were characterised by different techniques such as FTIR, UV–vis, AA, XPS, XRD and N2 adsorption at 77 K. They were screened as heterogeneous catalysts in the epoxidation of styrene using iodosylbenzene or m-chloroperbenzoic acid as oxidants. The encapsulated complexes show, in general, moderate alkene conversion (16–40%), but very poor enantiomeric excesses (ee% = 0–14); nevertheless, for complex I encapsulated into Al-TERG using PhIO as oxidant 14 ee% was obtained, which is higher than the value found for the homogeneous phase reaction run under comparable conditions. Characterisation of the catalyst materials after two run suggests partial collapsing of the clay pillars.

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