Mn(II)–amino acid complexes intercalated in CaAl-layered double hydroxide – Well-characterized, highly efficient, recyclable oxidation catalysts

• Synthesis of pristine and Mn–amino acid intercalated CaAl-LDHs by two methods.
• Identifying the samples having the complex exclusively among the layers of the LDH.
• Comprehensive characterization of the samples.
• Their application in mild oxidation reactions as efficient and recyclable catalysts.
• Increased activities and exclusive selectivities in epoxidation and cis diol formation.

Intercalated composite materials were prepared with CaAl-layered double hydroxide as the host and Mn(II)–amino acid (l-cysteine, l-histidine and l-tyrosine) complex anions as the guest. Two methods (intercalation of the ligand first followed by constructing the complex; preforming the complex first, then introducing it among the layers of the host) and optimization of the auxiliary conditions were performed to arrive at composites having the complex exclusively among the layers. The obtained substances were structurally characterized by powder X-ray diffractometry, mid IR spectroscopy in diffuse reflectance mode and with ATR or photoacoustic detections, and scanning electron microscopy. The structural features of the intercalant (coordination number, coordination sites) were elucidated by classical chemical and energy dispersive X-ray analyses, EPR, X-ray absorption and far IR spectroscopies. Structural models are also given. The catalytic activities, selectivities and recycling abilities of the substances were studied in the oxidation reactions of cyclohexene with peracetic acid and in situ formed iodosylbenzene as oxidants and allylic alcohol with peracetic acid, in the liquid phase. The intercalated substances proved to be efficient and highly selective (with peracetic acid: outstanding epoxide, with iodosylbenzene superior diol selectivities) catalysts with very good recycling abilities.

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