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Unprecedented dinuclear Robson type macrocyclic complexes having two plus III metal ions in two compartments and the role of the diimino moiety on the stability of metal ion oxidation states
Volume: 43
Issue: 42
Pages: 15737 - 15751
The work in this investigation deals with the syntheses, characterization, crystal structures and catechol oxidase activity of four diphenoxo-bridged Comte compounds of composition [(CoCoLMe-Pn)-Co-III-L-III-(N-3)(4)]center dot 6H(2)O (1), [(CoCoLMe-Pn)-Co-III-L-III-(N-3)(4)]center dot 4H(2)O (2), [(CoCoLMe-Pn)-Co-III-L-III-(N-3)(4)]center dot 3.5H(2)O (3) and [(CoCoLMe-Pn)-Co-III-L-III-(N-3)(4)]center dot 2.5H(2)O(N-3)(4)]center dot CH3CN"2.5H20 (4), and two diphenoxo-bridged ColliColl compounds of composition [(CoCoLMe-Pn)-Co-III-L-III-(N-3)(4)]center dot 2H(2)O) (5) and ((CoCoLMe-Pn)-Co-III-L-III-(N-3)(4)]center dot H2O (6). In these compounds, H2LMe-pn, H2LEt-pn, H2LMe-Me2pn and H-2(LEt-Me2Pn) are four Robson type tetraiminodiphenolate macrocyclic ligands, in which the superscript Me and Et indicate that the dialdehyde components are 4-methyl-2,6-diformylphenol and 4-ethyl-2,6-diformyl-phenol, respectively, white pn and Me2pn indicate that the diamine components are 1,3-diaminopropane and 2,2-dimethyl-1,3-diaminopropane, respectively. The Contour compounds 1-4 are further characterized by 1H NMR spectra. Compounds 1 and 3 are prepared following a metal-templated synthesis, while compounds 2 and 4 are prepared by direct synthesis, which includes using a pre-isolated macrocycle, [(CoCoLMe-Pn)-Co-III-L-III-(N-3)(4)]center dot 4H(2)O, as a reactant. On changing the diamine component of the corresponding macrocycie from 1,3-diaminopropane to 2,2-dimethyl-1,3diaminopropane, but otherwise following the similar reaction procedure (both direct and template), the ColliColl compounds [(CoCoLMe-Pn)-Co-III-L-III-(N-3)(4)]center dot 4H(2)O (5), [(CoCoLMe-Pn)-Co-III-L-III-(N-3)(4)]center dot 4H(2)O (6), [(CoCoLMe-Pn)-Co-III-L-III-(N-3)(4)]center dot 4H(2)O) (CoCoLMe-Pn)-Co-III-L-III-(N-3)(4)]center dot 4H(2)O (5A; lnorg. Chim. Acta, 2014, 412, 38) and [COIIIC011 LEt-Me2pn( IN) 3 I.MeCN (6A; Dalton Trans., 2013, 42, 4561) are formed, rather than Canton' compounds. Like compounds 5A and 6A, all the compounds 1-6 show catechol oxidase activity (substrate: 3,5-di-tert-butyl catechot). The kinetic parameters for 1, 3 and 6 have been determined. Their Kcat values are, respectively, 212.6, 188.0 and 191.3 h-1. ESI-MS (positive) spectra of some representative cases (with and without the substrate) have been recorded and the positive species have been assigned well. Unprecedented and surprising aspects of the composition/structure and properties of the complexes in this investigation have been discussed.
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JournalDalton Transactions