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

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](HL1a)2$4H2O (1), where (HL1a) ¼ 2-(SO3)C6H4(NH)N]C(C^N) (CONH2) is the carboxamide species derived from nucleophilic attack of water on a cyano group of (HL1). The copper tetramer [Cu4(H2O)10-(1kN:k2O:kO,2kN:kO-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 h1 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.