Department of Chemistry, University College of Science, University of Calcutta, 92, A. P.C. Road, Kolkata 700009, India.
Department of Chemistry, Government General Degree College at Kharagpur-II, Ambigeria, Madpur, Paschim Medinipur, 721149, West Bengal, India.
Dalton Trans. 2018 Jul 17;47(28):9385-9399. doi: 10.1039/c8dt01400k.
Three similar Mannich base ligands viz. N,N-bis(3,5-dimethyl-2-hydroxybenzyl)-N',N'-dimethyl-1,3-diaminopropane (H2L1), N,N-bis(3,5-dimethyl-2-hydroxybenzyl)-N',N'-dimethyl-1,2-diaminoethane (H2L2) and N,N-bis(3,5-dimethyl-2-hydroxybenzyl)-N',N'-diethyl-1,2-diaminoethane (H2L3) upon reaction with Cu(CH3COO)2·H2O produced dinuclear complexes [Cu2L21-3]. The reaction of each of these isolated dimeric species with Cu(ClO4)2·6H2O and NaN3 resulted in three new trinuclear complexes, [(CuL1)2(μ1,1-N3)2Cu(H2O)]·CH3OH (1), [(CuL2)2(μ1,1-N3)2Cu(H2O)]·CH3OH (2) and [(CuL3)2(μ1,1-N3)2Cu(H2O)]·2CH3OH (3), respectively. The complexes (1-3) have been characterized by elemental analysis and single crystal X-ray diffraction. In all three complexes, the central Cu(ii) ion is coordinated by two terminal [CuL] units through a phenoxido and an azido bridge. These are the first trinuclear Cu(ii) complexes of this type of Mannich base ligands. Magnetic susceptibility measurements showed intramolecular antiferromagnetic interactions with J = -64.42, -9.60 and -4.54 cm-1 for 1, 2 and 3, respectively. All three complexes exhibited catecholase-like and phenoxazinone synthase-like activities towards the aerobic oxidation of 3,5-di-tert-butylcatechol and o-aminophenol, respectively. The turnover numbers (kcat) for the aerobic oxidation of 3,5-di-tert-butylcatechol are 568.8, 542.1 and 500.4 h-1 and those of o-aminophenol are 125.83, 118.9 and 114.7 h-1 for complexes 1-3, respectively. The X-band EPR spectroscopy and estimation of the produced hydrogen peroxide indicated that the aerobic oxidation of 3,5-di-tert-butylcatechol proceeded through the formation of a semiquinonate radical. The mechanism of phenoxazinone synthase-like activities is also proposed for trinuclear Cu(ii) catalysts with the help of mass spectral analysis.
三种类似的曼尼希碱配体，即 N,N-双（3,5-二甲基-2-羟基亚苄基）-N',N'-二甲基-1,3-二氨基丙烷（H2L1）、N,N-双（3,5-二甲基-2-羟基亚苄基）-N',N'-二甲基-1,2-二氨基乙烷（H2L2）和 N,N-双（3,5-二甲基-2-羟基亚苄基）-N',N'-二乙基-1,2-二氨基乙烷（H2L3）与 Cu(CH3COO)2·H2O 反应生成双核配合物 [Cu2L21-3]。这些分离的二聚体物种中的每一种与 Cu(ClO4)2·6H2O 和 NaN3 反应，生成三个新的三核配合物，[(CuL1)2(μ1,1-N3)2Cu(H2O)]·CH3OH（1）、[(CuL2)2(μ1,1-N3)2Cu(H2O)]·CH3OH（2）和 [(CuL3)2(μ1,1-N3)2Cu(H2O)]·2CH3OH（3）。这些配合物（1-3）通过元素分析和单晶 X 射线衍射进行了表征。在所有三个配合物中，中心 Cu(ii) 离子通过一个苯氧基亚和一个叠氮桥与两个末端的[CuL]单元配位。这些是此类曼尼希碱配体的第一个三核 Cu(ii) 配合物。磁性测量表明，1、2 和 3 中存在分子内反铁磁相互作用，J 值分别为-64.42、-9.60 和-4.54 cm-1。所有三个配合物均表现出对 3,5-二叔丁基儿茶酚和邻氨基酚的有氧氧化的儿茶酚氧化酶样和苯并恶嗪酮合酶样活性。3,5-二叔丁基儿茶酚有氧氧化的转换数（kcat）分别为 568.8、542.1 和 500.4 h-1，邻氨基酚的转换数（kcat）分别为 125.83、118.9 和 114.7 h-1，用于配合物 1-3。X 波段 EPR 光谱和对产生的过氧化氢的估计表明，3,5-二叔丁基儿茶酚的有氧氧化是通过形成半醌自由基进行的。在质谱分析的帮助下，还提出了三核 Cu(ii) 催化剂的苯并恶嗪酮合酶样活性的机制。
