887511-91-3Relevant academic research and scientific papers
Carboxylate and alkyl carbonate coordination at the hydrophobic binding site of redox-active dicobalt amine thiophenolate complexes
Kersting, Berthold,Steinfeld, Gunther
, p. 1140 - 1150 (2002)
A series of new dicobalt complexes of the permethylated macrocyclic hexaamine dithiophenolate ligand H2LMe have been prepared and investigated in the context of ligand binding and oxidation state changes. The octadentate ligand is an effective dinucleating ligand that supports the formation of bioctahedral complexes with a central N3Co(μ-SR)2(μ-X)CoN3 core structure, leaving a free bridging position X for the coordination of the substrates. The acetato- and cinnamato-bridged complexes [(LMe)CoII2(μ-O2CMe)] + (2) and [(LMe)CoII2(μ-O2CCH=CHPh)] + (5) were prepared by reaction of the μ-Cl complex [(LMe)COII2(μ-Cl)]+ (1) with the corresponding sodium carboxylates in methanol. The electrochemical properties of these and of the methyl carbonate complex [(LMe)CoII2(μ-O2COMe)] + (8) were also investigated. All complexes undergo two stepwise oxidations at ca. E11/2 = +0.22 and at E21/2 = ca. +0.60 V vs SCE, affording the mixed-valent complexes [(LMe)CoIICoIII(μ-O2CR)] 2+ (3, 6, 9) and the fully oxidized CoIIICoIII forms [(LMe)CoIII2(μ-O2CR)] 3+ (4, 7, 10), respectively. Compounds 3, 6, 9 and 4, 7, 10 refer to acetato-, cinnamato-, and methylcarbonato species, respectively. The CoIICoIII compounds were prepared by comproportionation of the respective CoII2 and CoIII2 compounds. The CoIIICoIII species were prepared by bromine oxidation of the CoIICoII forms. The crystal structures of complexes 2·BPh4·MeCN, 3·(l3)2, 5·BPh4·2MeCN, 6·(ClO4)2·EtOH, 7· (ClO4)3·MeCN·(H2O) 3, and 9·(ClO4)2·(MeOH)2·H 2O were determined by single-crystal X-ray crystallography at 210 K. The oxidations occur without gross structural changes of the parent complexes. The CoIICoIII complexes are composed of high-spin CoII (d7) and low-spin CoIII (d6) ions. The CoIIICoIII complexes are diamagnetic. The oxidation reactions affect the binding mode of the substrates. In the CoII2 and CoIICoIII forms the carboxylates bridge the two Co2+ ions in a symmetric μ-1,3 fashion with uniform C-O bond distances, whereas asymmetric bridging modes, with one short C=O and one long C-O distance, are adopted in the fully oxidized species. This is consistent with the observed shifts in vibrational frequencies for νas(C-O) and ν s(C-O) across the series.
