Cu(II)-amino acid–CaAl-layered double hydroxide complexes, recyclable, efficient catalysts in various oxidative transformations

• Synthesis of pristine and Cu-amino acid intercalated CaAl-LDHs by two methods.
• Selecting the samples having the complex exclusively among the layers of the LDH.
• State-of-the-art characterization of the samples.
• Their application in mild oxidation reactions and in Ullmann coupling.
• The selected samples proved to be efficient and recyclable catalysts.

Intercalated composite materials were prepared with CaAl-layered double hydroxide as host and Cu(II)-amino acid (l-cysteine, l-histidine and l-tyrosine) complex anions as guests. 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 synthesis conditions were performed to obtain composites having the complex exclusively among the layers. The composite materials were structurally characterized by powder X-ray diffractometry, mid infrared (IR) spectroscopy with ATR (attenuated total reflectance) or photoacoustic detections, transmission and scanning electron microscopies and X-ray photoelectron spectroscopy. Structural features of the intercalant (coordination number, coordination sites) were elucidated by classical chemical and energy dispersive X-ray analyses, EPR (electron paramagnetic spectroscopy), X-ray absorption and far IR spectroscopies. Structural models based on these methods are also given. 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 in the liquid phase. The catalysts were active in the Ullmann coupling reaction as well. The intercalated substances were found to be efficient and highly selective catalysts with very good recycling abilities.

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