Dinuclear mixed-valence Co~(III)Co~(II) complexes derived from a macrocyclic ligand: Unique example of a Co~(III)Co~(II) complex showing catecholase activity

摘要

The work in this paper presents the syntheses, characterization, catecholase activity, and electrospray ionization mass spectroscopic (ESI-MS positive) study of three mixed-valence dinuclear Co~(III)Co~(II) complexes of composition [Co~(III)Co~(II)L(N_3) _3]·CH_3CN (1), [Co~(III)Co ~(II)L(OCN)_3]·CH_3CN (2), and [Co ~(III)Co~(II)L(μ-CH_3COO)_2](ClO _4) (3), derived from a tetraimino diphenolate macrocyclic ligand H_2L, obtained on [2 + 2] condensation of 4-ethyl-2,6-diformylphenol and 2,2′-dimethyl-1,3-diaminopropane. While 1 and 2 are diphenoxo-bridged, 3 is a heterobridged bis(μ-phenoxo)bis(μ-acetate) system. Utilizing 3,5-di-tert-butyl catechol (3,5-DTBCH_2) as the substrate, the catecholase activity of all the three complexes has been checked in methanol/acetonitrile/N,N-dimethyl formamide. While 2 and 3 are inactive, complex 1 shows catecholase activity with turnover numbers of 482.16 h ~(-1) and 45.38 h~(-1) in acetonitrile and methanol, respectively. Electrospray ionization mass (ESI-MS positive) spectra of complexes 1-3 have been recorded in acetonitrile solutions and the positive ions have been well characterized. The ESI-MS positive spectrum of complex 1 in the presence of 3,5-DTBCH_2 has also been recorded and, interestingly, two positive ions [Co~(III)Co~(II)L(N_3) _2(3,5-DTBCH~-)H]~+ and [Co~(II)Co ~(II)L(μ-3,5-DTBCH~(2-))Na]~+ have been identified.