Bis(μ-alkoxo) bridged dinuclear CuII2 and ZnII2 complexes of an isoindol functionality based new ligand: Synthesis, structure, spectral characterization, magnetic properties and catechol oxidase activity

Aerial Oxidation of Phenol/Catechol in the Presence of Catalytic Amounts of [(Cl)2Mn(RCOOET)], RCOOET= Ethyl-5-Methyl-1-(((6-Methyl-3-Nitropyridin-2-yl)Amino)Methyl)-1H-Pyrazole-3-Carboxylate

In this work, we report on the catalytic activity of a manganese complex [(Cl)2Mn(RCOOET)], where RCOOET is ethyl-5-methyl-1-(((6-methyl-3-nitropyridin-2-yl)amino)methyl)-1H-pyrazole-3-carboxylate, in the oxidation of phenol or catechol by atmospheric oxygen to form o-quinone. The [(Cl)2Mn(RCOOET)] catalyzes the oxidation of catechol at a rate of 3.74 µmol L−1 min−1 in tetrahydrofuran (THF), in a similar manner to catecholase or tyrosinase.

Oxygen Delivery as a Limiting Factor in Modelling Dicopper(II) Oxidase Reactivity

Deprotonation of ligand-appended alkoxyl groups in mononuclear copper(II) complexes of N,O ligands L₁ and L₂ , gave dinuclear complexes sharing symmetrical Cu₂ O₂ cores. Molecular structures of these mono- and binuclear complexes have been characterized by XRD, and their electronic structures by UV/Vis, ¹ H NMR, EPR and DFT; moreover, catalytic performance as models of catechol oxidase was studied. The binuclear complexes with anti-ferromagnetically coupled copper(II) centers are moderately active in quinone formation from 3,5-di-tert-butyl-catechol under the established conditions of oxygen saturation, but are strongly activated when additional dioxygen is administered during catalytic turnover. This unforeseen and unprecedented effect is attributed to increased maximum reaction rates v_max , whereas the substrate affinity K_M remains unaffected. Oxygen administration is capable of (partially) removing limitations to turnover caused by product inhibition. Because product inhibition is generally accepted to be a major limitation of catechol oxidase models, we think that our observations will be applicable more widely.

Vanadium(V) complexes of a tripodal ligand, their characterisation and biological implications

The reaction of the tripodal tetradentate dibasic ligand 6,6'-(2-(pyridin-2-yl)ethylazanediyl)bis(methylene)bis(2,4-di-tert-butylphenol), H2L(1)I, with [V(IV)O(acac)2] in CH3CN gives the V(V)O-complex, [V(V)O(acac)(L(1))] 1. Crystallisation of 1 in CH3CN at ∼0 °C gives dark blue crystals of 1, while at room temperature it affords dark green crystals of [{V(V)O(L(1))}2μ-O] 3. Upon prolonged treatment of 1 in MeOH, [V(V)O(OMe)(MeOH)(L(1))] 2 is obtained. All three complexes were analysed by single-crystal X-ray diffraction, depicting a distorted octahedral geometry around vanadium. In the reaction of H2L(1) with V(IV)OSO4 partial hydrolysis of the tripodal ligand results in the elimination of the pyridyl fragment of L(1) and the formation of H[V(V)O2(L(2))] 4 containing the ONO tridentate ligand 6,6'-azanediylbis(methylene)bis(2,4-di-tert-butylphenol), H2L(2)II. Compound 4, which was not fully characterised, undergoes dimerization in acetone yielding the hydroxido-bridged [{V(V)O(L(2))}2μ-(OH)2] 5 having a distorted octahedral geometry around each vanadium. In contrast, from a solution of 4 in acetonitrile, the dinuclear compound [{V(V)O(L(2))}2μ-O] 6 is obtained, with a trigonal bipyramidal geometry around each vanadium. The methoxido complex 2 is successfully employed as a functional catechol-oxidase mimic in the oxidation of catechol to o-quinone under air. The process was confirmed to follow a Michaelis-Menten type kinetics with respect to catechol, the Vmax and KM values obtained being 7.66 × 10(-6) M min(-1) and 0.0557 M, respectively, and the turnover frequency is 0.0541 min(-1). A similar reaction with the bulkier 3,5-di-tert-butylcatechol proceeded at a much slower rate. Complex 2 was also used as a catalyst precursor for the oxidative bromination of thymol in aqueous medium. The selectivity shows quite interesting trends, namely when not using excess of the primary oxidizing agent, H2O2, the para mono-brominated product corresponds to ∼93% of the products and no dibromo derivative is formed.

Hydrolytically active tetranuclear [NiII2]2 complexes: synthesis, structure, spectroscopy and phosphoester hydrolysis

Hydrolytically active three tetranuclear nickel(ii) complexes of a new symmetrical μ-bis(tetradentate) ligand, H₅chdp were prepared and their catalytic activity toward the phosphoester hydrolysis was examined.