Copper complexes with ferrocenyl pendants: Evidence for an FeII ∼ CuII ⇌ FeIII ∼ CuI electron transfer equilibrium leading to a reaction with dioxygen
作者:Andrew J. Evans、Scott E. Watkins、Donald C. Craig、Stephen B. Colbran
DOI:10.1039/b105150b
日期:2002.3.8
Three new nitrogen-donor ligands with ferrocenyl pendants, namely ferrocenylmethylbis(2-pyridylethyl)amine (L1), ferrocenylmethylbis(2-pyridylmethyl)amine (L2), and 1-ferrocenylmethyl-4,7-diisopropyl-1,4,7-triazacyclononane (L3), have been synthesised. Copper(II) complexes of these ligands have been made and their physicochemical and redox properties characterised. Crystal structures of [Cu(L2)X2·0.5Et2O (X = Cl, Br), [Cu(L2)(OTf)2(CH3OH)], [Cu(L3)Cl2], and [(L3)Cu}2(μ-OH)2](OTf)2·0.5Et2O are reported. Oxidation of each complex with ceric ion affords the corresponding FeIII
â¼ CuII species. Variations in ligand design, the choice of co-ligand (chloride, bromide, trifluoromethanesulfonate
(OTf) or solvent) and the choice of solvent allowed, in the case of acetonitrile solutions of [Cu(L1)(H2O)2](OTf)2, the close matching of the FeIIIâFeII and CuIIâCuI electrochemical couples. [Cu(L1)(H2O)2](OTf)2 reacts with dioxygen in acetonitrile, but is stable in other solvents such as tetrahydrofuran. Electronic spectra of the complex in acetonitrile exhibit a prominent ferrocenium ion band. These results are interpreted in terms of an intramolecular electron transfer equilibrium between FeII
â¼ CuII and FeIII
â¼ CuI tautomers for the complex that leads to it reacting with dioxygen; their possible biological relevance is discussed.
合成了三种具有二茂铁基配体的氮供体型配体,即二茂铁基甲基双(2-吡啶乙基)胺(L1)、二茂铁基甲基双(2-吡啶甲基)胺(L2)和1-二茂铁基甲基-4,7-二异丙基-1,4,7-三氮杂环壬烷(L3)。这些配体的铜(II)配合物被制备并表征了它们的物化性质和氧化还原性质。报道了[Cu(L2)X2·0.5Et2O (X = Cl, Br)、[Cu(L2)(OTf)2(CH3OH)]、[Cu(L3)Cl2]和[(L3)Cu}2(μ-OH)2](OTf)2·0.5Et2O的晶体结构。用铈离子氧化每个配合物会得到相应的FeIII≈CuII物种。配体设计的变体、配体的选择(氯化物、溴化物、三氟甲磺酸盐(OTf)或溶剂)和溶剂的选择使得[Cu(L1)(H2O)2](OTf)2的乙腈溶液的FeIII-FeII和CuII-CuI电化学耦合能够紧密匹配。[Cu(L1)(H2O)2](OTf)2在乙腈中与氧气反应,但在四氢呋喃等其他溶剂中稳定。该配合物在乙腈的电子光谱显示出明显的二茂铁离子带。这些结果被解释为配合物中FeII≈CuII与FeIII≈CuI异构体之间的分子内电子转移平衡,导致其与氧气反应;并讨论了它们可能的生物学相关性。