Dinuclear Mn(ii,ii) complexes: magnetic properties and microwave assisted oxidation of alcohols
作者:Manas Sutradhar、Luísa M. D. R. S. Martins、M. Fátima C. Guedes da Silva、Elisabete C. B. A. Alegria、Cai-Ming Liu、Armando J. L. Pombeiro
DOI:10.1039/c3dt52774c
日期:——
A series of six new mixed-ligand dinuclear Mn(II,II) complexes of three different hydrazone Schiff bases (H3L1, H3L2 and H3L3), derived from condensation of the aromatic acid hydrazides benzohydrazide, 2-aminobenzohydrazide or 2-hydroxybenzohydrazide, with 2,3-dihydroxy benzaldehyde, respectively, is reported. Reactions of Mn(NO3)2·4H2O with the H3L1–3 compounds, in the presence of pyridine (1 : 1 : 1 mole ratio), in methanol at room temperature, yield [Mn(H2L1)(py)(H2O)]2(NO3)2·2H2O (1·2H2O), [Mn(H2L2)(py)(CH3OH)]2(NO3)2·4H2O (2·4H2O) and [Mn(H2L3)(py)(H2O)]2(NO3)2 (3) respectively, whereas the use of excess pyridine yields complexes with two axially coordinated pyridine molecules at each Mn(II) centre, viz. [Mn(H2L1)(py)2]2(NO3)2·H2O (4·H2O), [Mn(H2L2)(py)2]2(NO3)2·2H2O (5·2H2O) and [Mn(H2L3)(py)2]2(NO3)2·2CH3OH (6·2CH3OH), respectively. In all the complexes, the (H2L1–3)− ligand coordinates in the keto form. Complexes 1·2H2O, 2·4H2O, 4·H2O, 5·2H2O and 6·2CH3OH are characterized by single crystal X-ray diffraction analysis. The complexes 1, 2 and 6, having different coordination environments, have been selected for variable temperature magnetic susceptibility measurements to examine the nature of magnetic interaction between magnetically coupled Mn(II) centres and also for exploration of the catalytic activity towards microwave assisted oxidation of alcohols. A yield of 81% (acetophenone) is obtained using a maximum of 0.4% molar ratio of catalyst relative to the substrate in the presence of TEMPO and in aqueous basic solution, under mild conditions.
本论文报告了由芳香酸酰肼苯甲酰肼、2-氨基苯甲酰肼或 2-羟基苯甲酰肼分别与 2,3-二羟基苯甲醛缩合而成的三种不同的腙席夫碱(H3L1、H3L2 和 H3L3)的六种新的混合配体双核锰(II,II)配合物系列。Mn(NO3)2-4H2O 与 H3L1-3 化合物在吡啶(1 : 1 : 摩尔比)的情况下,在室温下于甲醇中分别生成 [Mn(H2L1)(py)(H2O)]2(NO3)2-2H2O (1-2H2O)、[Mn(H2L2)(py)(CH3OH)]2(NO3)2-4H2O (2-4H2O) 和 [Mn(H2L3)(py)(H2O)]2(NO3)2 (3)、而使用过量的吡啶则会产生在每个锰(II)中心有两个轴向配位吡啶分子的配合物,即分别是 [Mn(H2L1)(py)2]2(NO3)2-H2O(4-H2O)、[Mn(H2L2)(py)2]2(NO3)2-2H2O(5-2H2O)和 [Mn(H2L3)(py)2]2(NO3)2-2CH3OH(6-2CH3OH)。在所有配合物中,(H2L1-3)- 配体都以酮形式配位。络合物 1-2H2O、2-4H2O、4-H2O、5-2H2O 和 6-2CH3OH 通过单晶 X 射线衍射分析进行了表征。我们选择了具有不同配位环境的配合物 1、2 和 6 进行变温磁感应测量,以研究磁耦合锰(II)中心之间磁相互作用的性质,并探索微波辅助氧化醇的催化活性。在 TEMPO 存在和碱性水溶液中,在温和条件下,催化剂与底物的摩尔比最大为 0.4%,可获得 81% 的产率(苯乙酮)。