Ghosh Debalina, Mukherjee Rabindranath
Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India.
Inorg Chem. 1998 Dec 28;37(26):6597-6605. doi: 10.1021/ic9713689.
A full account of a chemical system possessing features that mimic the reactivity aspects of tyrosinase is presented. Using dinucleating ligands with a m-xylyl spacer three new dicopper(I) complexes have been synthesized and their reactivity with dioxygen investigated. The six-membered chelate ring forming ligands provide only two nitrogen coordinations to each copper. The complexes [Cu(I)(2)L(CH(3)CN)(2)]X(2) (X = ClO(4)(-) (1a), SbF(6)(-) (1b)) and [Cu(I)(2)(L-NO(2))(CH(3)CN)(2)]SbF(6) (1c) [L = alpha,alpha'-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene; L-NO(2) = para-nitro derivative of L] have been characterized by IR and (1)H NMR spectroscopy. The reaction of O(2) with 1a-c in CH(2)Cl(2) or THF is instantaneous and causes stoichiometric xylyl hydroxylation reactions producing phenol products. Thus 1a produces phenoxo-/hydroxo-bridged product [Cu(II)(2)(L-O)(OH)]ClO(4) (2a). The existence of putative peroxo-dicopper(II) species could not be detected even at -80 degrees C. A trend is observed for the extent of aromatic ring hydroxylation (298 K): CH(3)CN approximately DMF > CH(3)OH >> CH(2)Cl(2). Cyclic voltammetric experiment of 1a in DMF reveals an appreciably low redox potential (E(1/2) = -0.26 V vs SCE) for the Cu(II)(2)/Cu(I)(2) redox process. Variable-temperature (25-300 K) magnetic susceptibility measurements establish that the copper(II) centers in 2a and the dihydroxo-bridged complex [Cu(II)(2)L'(OH)(2)]ClO(4) (2b) [formed due to an impurity (L') present during the synthesis of L following Method A; L' = bis[alpha,alpha'-bis(N-methyl-N-(2-pyridylethyl)amino)-m-xylene]methylamine] are antiferromagnetically coupled, with 2a considerably more coupled than 2b. Reaction of 1a with O(2) in CH(2)Cl(2) (298 K) produces an additional unhydroxylated product of composition [Cu(II)(2)L(OH)(OH(2))]ClO(4).2H(2)O.0.5HCl (3a). In agreement with its proposed hydroxo-/aquo-bridged structure, 3a is weakly antiferromagnetically coupled. In CH(3)CN solution, 3a rearranges to generate a doubly hydroxo-bridged species Cu(II)(2)L(OH)(2). Using a solution-generated dicopper(I) complex of a closely similar ligand (L' ') providing five-membered chelate ring, the reactivity toward dioxygen was also investigated. It produces only an irreversibly oxidized product of composition Cu(II)(2)L' '(OH)(ClO(4))(3)(H(2)O)(2) (3b) (L' ' = alpha,alpha'-bis[N-methyl-N-(2-pyridylmethyl)amino]-m-xylene). For 3b the copper(II) centers are almost uncoupled.
本文全面介绍了一个具有模仿酪氨酸酶反应特性的化学体系。使用带有间二甲苯间隔基的双核配体合成了三种新型二价铜（I）配合物，并研究了它们与氧气的反应性。形成六元螯合环的配体为每个铜仅提供两个氮配位。配合物[Cu（I）₂L（CH₃CN）₂]X₂（X = ClO₄⁻（1a），SbF₆⁻（1b））和[Cu（I）₂（L-NO₂）（CH₃CN）₂][SbF₆]₂（1c）[L = α，α'-双[N-甲基-N-（2-吡啶基乙基）氨基]-间二甲苯；L-NO₂ = L的对硝基衍生物]已通过红外光谱和¹H核磁共振光谱进行了表征。O₂与1a - c在CH₂Cl₂或THF中的反应瞬间发生，并导致化学计量的二甲苯羟基化反应生成酚类产物。因此，1a生成苯氧基/羟基桥联产物[Cu（II）₂（L-O）（OH）][ClO₄]₂（2a）。即使在-80℃也未检测到假定的过氧二价铜（II）物种的存在。观察到芳环羟基化程度的趋势（298K）：CH₃CN≈DMF＞CH₃OH＞＞CH₂Cl₂。1a在DMF中的循环伏安实验表明，Cu（II）₂/Cu（I）₂氧化还原过程的氧化还原电位明显较低（E₁/₂ = -0.26V对SCE）。变温（25 - 300K）磁化率测量表明，2a中的二价铜中心和二羟基桥联配合物[Cu（II）₂L'（OH）₂][ClO₄]₂（2b）[由于在方法A合成L期间存在的杂质（L'）形成；L' = 双[α，α'-双（N-甲基-N-（2-吡啶基乙基）氨基）-间二甲苯]甲胺]是反铁磁耦合的，2a的耦合程度比2b大得多。1a与O₂在CH₂Cl₂（298K）中的反应产生了一种额外的未羟基化产物，其组成为[Cu（II）₂L（OH）（OH₂）][ClO₄]₃·₂H₂O·0.5HCl（3a）。与其提出的羟基/水桥联结构一致，3a是弱反铁磁耦合的。在CH₃CN溶液中，3a重排生成双羟基桥联物种[Cu（II）₂L（OH）₂]²⁺。使用具有紧密相似配体（L''）的溶液生成的二价铜（I）配合物，其提供五元螯合环，也研究了其与氧气的反应性。它仅产生一种组成不可逆氧化产物Cu（II）₂L''（OH）（ClO₄）₃（H₂O）₂（3b）（L'' = α，α'-双[N-甲基-N-（2-吡啶基甲基）氨基]-间二甲苯）。对于3b，二价铜中心几乎未耦合。
