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A family of ligand and anion dependent structurally diverse Cu(II) Schiff-base complexes and their catalytic efficacy in an O-arylation reaction in ethanolic media

机译:一族依赖配体和阴离子的结构多样的Cu(II)Schiff碱配合物及其在乙醇介质中O-芳基化反应中的催化效率

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摘要

Two nitrato bridged dinuclear systems [Cu-2(L1)(2)(NO3)(3)] NO3 center dot H2O (1) and [Cu-2(L-2)(2)(NO3)(3)] NO3 center dot MeOH (2), five monomeric complexes viz. [Cu(L-3)(NO3)]NO3 (3), [Cu(L-4)(NO3)]NO3 (4), [Cu(L-5)(NO3)]NO3 (5), [Cu(L-6)(NO3)NO3] (7), [Cu(L7)(NO3)]NO3 (8) and one hetero bi-bridged (phenoxido and water) dinuclear complex [Cu-2(L-2)(2)(H2O)(2)](ClO4)(4)center dot 4H(2)O (6) have been synthesized and characterized using several physicochemical methods (L1 = 1-(N-3-methoxysalicylideneimino)-ethane-2-piperazine, L2 =1 -(N-3-ethoxysalicylideneimino)-ethane- 2-piperazine, L3 = 1-(N-4'-ethoxy-alpha-methylasalicylideneimino)-ethane-2-piperazine, L4 = 1-(N-5'-chloro-alpha-methylasalicylideneimino)-ethane-2-piperazine, L5 = 1-(N-5-chlorosalicylideneimino)-ethane-2-piperazine, L6 = 1-(N-4-methoxysalicylideneimino)-ethane-2-piperazine and L7 = 1-(N-40-methoxy-amethylasalicylideneimino)-ethane-2-piperazine). X-ray structural analysis showed that complexes 1 and 2 are discrete dinuclear species where the pentacoordinated metal centers are bridged through a nitrate ion. In 3, 4, 5 and 8 the monomeric copper center displays a square pyramidal geometry with a weak axial Cu-O bond. In 7, the monomeric copper center shows a distorted octahedral geometry with two coordinated nitrate anions. However, in 6 the two copper centers coordinate in different manners (one is square-pyramidal and the other is distorted octahedral) and are bridged through a phenoxido group and a water molecule. All complexes efficiently catalyze the C-O coupling reaction under homogeneous conditions at 80 degrees C to afford unsymmetrical diaryl ethers using nitroarenes to act as an excellent electrophile. Notably, the reaction is carried out in ethanol media which facilitates the avoidance of toxic wastes. Structurally diverse copper(II) Schiff-base complexes have rarely been used systematically in catalytic C-O coupling reactions.
机译:两个硝酸根桥接双核系统[Cu-2(L1)(2)(NO3)(3)] NO3中心点H2O(1)和[Cu-2(L-2)(2)(NO3)(3)] NO3中心点MeOH(2),五个单体配合物。 [Cu(L-3)(NO3)] NO3(3),[Cu(L-4)(NO3)] NO3(4),[Cu(L-5)(NO3)] NO3(5),[Cu (L-6)(NO3)NO3](7),[Cu(L7)(NO3)] NO3(8)和一种杂双桥联(苯氧和水)双核络合物[Cu-2(L-2)( 2)(H2O)(2)](ClO4)(4)中心点4H(2)O(6)已通过几种物理化学方法合成和表征(L1 = 1-(N-3-甲氧基水杨基亚氨基)-乙烷-2 -哌嗪,L2 = 1-(N-3-乙氧基水杨酰亚胺亚胺基)-乙烷-2-哌嗪,L3 = 1-(N-4'-乙氧基-α-甲基水杨基亚胺基)-乙烷-2-哌嗪,L4 =​​ 1-(N -5'-氯-α-甲基水杨基亚氨基)-乙烷-2-哌嗪,L5 = 1-(N-5-氯水杨基亚胺基)-乙烷-2-哌嗪,L6 = 1-(N-4-甲氧基水杨基亚胺基)-乙烷-2 -哌嗪和L7 = 1-(N-40-甲氧基-甲基水杨基亚氨基)-乙烷-2-哌嗪)。 X射线结构分析表明,配合物1和2是离散的双核物种,其中五配位金属中心通过硝酸根离子桥接。在3、4、5和8中,单体铜中心呈方形金字塔形几何形状,且具有较弱的轴向Cu-O键。在7中,单体铜中心显示出扭曲的八面体几何形状,带有两个配位的硝酸根阴离子。但是,在6中,两个铜中心以不同的方式进行配位(一个为方形金字塔形,另一个为扭曲的八面体形),并通过一个苯氧羰基和一个水分子桥接。使用硝基芳烃作为优异的亲电试剂,所有络合物均能在均相条件下于80摄氏度下有效催化C-O偶联反应,从而得到不对称的二芳基醚。值得注意的是,该反应在乙醇介质中进行,这有助于避免有毒废物。结构多样的铜(II)席夫碱配合物很少用于催化C-O偶联反应。

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