MnII and CuII complexes with arylhydrazones of active methylene compounds as effective heterogeneous catalysts for solvent- and additive-free microwave-assisted peroxidative oxidation of alcohols

Abstract

A one-pot template reaction of sodium 2-(2-(dicyanomethylene)hydrazinyl)benzenesulfonate (NaHL¹) with water and manganese(II) acetate tetrahydrate led to the mononuclear complex [Mn(H₂O)₆](HL^1a)₂·4H₂O (1), where (HL^1a)⁻ = 2-(SO₃⁻)C₆H₄(NH)NC(CN) (CONH₂) is the carboxamide species derived from nucleophilic attack of water on a cyano group of (HL¹)⁻. The copper tetramer [Cu₄(H₂O)₁₀(1κN:κ²O:κO,2κN:κO-L²)₂]·2H₂O (2) was obtained from reaction of Cu(NO₃)₂·2.5H₂O with sodium 5-(2-(4,4-dimethyl-2,6-dioxocyclohexylidene)hydrazinyl)-4-hydroxybenzene-1,3-disulfonate (Na₂H₂L²). Both complexes were characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray diffraction. They exhibit a high catalytic activity for the solvent- and additive-free microwave (MW) assisted oxidation of primary and secondary alcohols with tert-butylhydroperoxide, leading to yields of the oxidized products up to 85.5% and TOFs up to 1.90 × 10³ h⁻¹ after 1 h under low power (5–10 W) MW irradiation. Moreover, the heterogeneous catalysts are easily recovered and reused, at least for three consecutive cycles, maintaining 89% of the initial activity and a high selectivity.