Crystal structure, catecholase activity and ESI-MS of a mixed valence cobalt(III)–cobalt(II) complex derived from a macrocyclic ligand: Identification/proposition of hydrogen bonded metal complex⋯solvent aggregates in ESI-MS

Abstract

This paper presents the synthesis, crystal structure, catechol oxidase activity and electrospray ionization mass spectra (ESI-MS positive) of a mixed-valence CoIIICoII compound [CoIIICoIIL(N3)3]· 0.5CH3CN·0.27H2O (1) derived from the Robson type tetraiminodiphenolate macrocyclic ligand H2L, which is the [2+2] condensation product of 2,6-diformyl-4-methylphenol and 2,2-dimethyl-1,3-diaminopropane. Compound 1 crystallizes in the monoclinic P21/n space group. The structure consists of two independent units of diphenoxo-bridged CoIIICoII moieties where the CoIII center is hexacoordinated (distorted octahedral) having O(phenoxo)2N(imine)2N(azide)2 environment, while CoII center is pentacoordinated (distorted square pyramidal) having O(phenoxo)2N(imine)2N(azide) environment. Catechol oxidase activity of 1 has been investigated using 3,5-di-tert-butylcatechol (3,5-DTBCH2) as the substrate, revealing that it is an active catalyst with Kcat value 114.24h–1. Electrospray ionization mass spectra (ESI-MS positive) of 1 and 1+3,5-DTBCH2 in acetonitrile have been recorded. No complex⋯substrate aggregate in the spectrum of 1+3,5-DTBCH2 has been identified. However, interestingly, two hydrogen bonded metal complex⋯solvent aggregates [{CoII(LH2)(N3)}⋯(CH3CN)]+ and [{CoIII(LH2)(N3)2}⋯(CH3CN)]+ have been identified in the spectrum of 1. Catecholase activity has also been studied with pyrocatechol and tetrachlorocatechol (TCCH2) as substrates. While no activity has been found with TCCH2, weak activity has been observed with pyrocatechol.