Dinuclear mixed-valence CoIIICoII complexes derived from a macrocyclic ligand: unique example of a CoIIICoII complex showing catecholase activity

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 (CoCoII)-Co-III complexes of composition [(CoCoL)-Co-III-L-II(N-3)(3)]center dot CH3CN (1), [(CoCoL)-Co-III-L-II(OCN)(3)]center dot CH3CN (2), and [(CoCoL)-Co-III-L-II(mu-CH3COO)(2)](ClO4) (3), derived from a tetraimino diphenolate macrocyclic ligand H2L, 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(mu-phenoxo)bis(mu-acetate) system. Utilizing 3,5-di-tert-butyl catechol (3,5-DTBCH2) 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-DTBCH2 has also been recorded and, interestingly, two positive ions [(CoCoL)-Co-III-L-II(N-3)(2)(3,5-DTBCH-)H](+) and [(CoCoL)-Co-II-L-II(mu-3,5-DTBCH2-)Na](+) have been identified.