Solvent Dependent Disproportionation of Cu(II) Complexes of N2O2-Type Ligands: Direct Evidence of Formation of Phenoxyl Radical: An Experimental and Computational Study
作者:Rajib Kumar Debnath、Apurba Kalita、Sourab Sinha、Pradip Kr. Bhattacharyya、Biplab Mondal、Jatindra Nath Ganguli
DOI:10.14233/ajchem.2015.19193
日期:——
Four Cu(II) complexes (1, 2, 3 and 4) with N2O2-type ligand, H2L1, H2L2, H2L3 and H2L4, respectively have been synthesized as the functional model for galactose oxidase. In presence of acetonitrile the Cu(II) centres in the complexes, undergo reduction with simultaneous oxidation of the ligands. The ligand oxidized products are isolated and characterized. Spectroscopic studies indicate that this disproportionation goes through the formation of a Cu(II)-phenoxyl intermediate. The complexes also undergoes the same reaction with pyridine, which indicates the involvement of the exergonic N-donor ligand for the formation of Cu(II)-phenoxyl complex. The Cu(II)-phenoxyl complexes are found to be stable in methanol in presence of a strong base. The paramagnetic centers in the Cu(II)-phenoxyl complexes were found to be weakly ferromagnetically coupled. The complexes, in acetonitrile solvent, have been found to oxidize primary alcohols to corresponding aldehydes. In absence of single crystal structures of the complexes, we optimized the structures using density functional theory (DFT). The UV-visible peaks of complexes as found from time dependent density functional theory (TDDFT) calculations match well with the observed experimental results.
合成了四种Cu(II)络合物(1, 2, 3和4),其配体为N2O2型的H2L1、H2L2、H2L3和H2L4,作为乳糖氧化酶的功能模型。在乙腈存在下,络合物中的Cu(II)中心发生还原,同时配体被氧化。氧化的配体产物被分离并进行表征。光谱研究表明,这一不均化反应是通过形成Cu(II)-苯氧基中间体进行的。这些络合物在吡啶存在下也发生同样反应,表明外能量N-供体配体参与了Cu(II)-苯氧基络合物的形成。Cu(II)-苯氧基络合物在强碱存在下在甲醇中被发现是稳定的。Cu(II)-苯氧基络合物中的顺磁中心被发现弱耦合成铁磁性。在乙腈溶剂中,这些络合物能够将初级醇氧化为相应的醛。在缺乏单晶结构的情况下,我们使用密度泛函理论(DFT)对其结构进行了优化。从时间相关密度泛函理论(TDDFT)计算中获得的络合物的紫外-可见光谱峰与观察到的实验结果良好匹配。