Highly efficient heterogeneous catalysts for phenol oxidation: Binuclear pyrrolyl-azine metal complexes encapsulated in NaY zeolite

• Binuclear Cu(II) and Fe(II) complexes in NaY were prepared and characterised.
• DFT study confirms the geometry of the complexes formed.
• The catalysts are effective in achieving phenol hydroxylation.
• Higher conversion on phenol to catechol was obtained by the heterogeneous catalysts.
• Fe(II) heterogeneous catalysts lead to total conversion of phenol.

Phenol was successfully oxidized by the heterogeneous catalysts based on iron(II) or copper(II) pyrrolyl-azine complexes encapsulated into NaY zeolite, under mild conditions. The heterogeneous catalysts were prepared using two different methods and characterized by different spectroscopic techniques and chemical analysis. The pyrrolyl-azine complexes are formed with a metal/ligand molar ratio of 2:1. Their structures were further confirmed by DFT calculations. The catalytic experimental conditions (e.g., amount of catalyst, presence or absence of the oxidant, PhOH:tBuOOH molar ratio) were optimized. The presence of the encapsulated metal pyrrolyl-azine complexes in NaY zeolite enhances higher conversion of phenol to catechol. The catalytic activities of the encapsulated metal complexes in NaY zeolite were compared with the homogeneous counterpart, and the catalysts were easily recovered and reused.

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