对系列手性salen-Ni(Ⅱ)络合物的电子圆二色(ECD)光谱及其绝对构型关联进行了概述.根据晶体结构和对固、液ECD光谱的表征,结合理论计算,着重探讨了准平面型手性[Ni(salen)]的固态结构及其在溶液中的绝对构型和优势构象.在此基础上通过若干实例说明了平面四方形[M(Salen)]络合物两种绝对构型命名法,并给出了我们的建议.对[Ni(sal-R,R-chxn)][sal-R,R-chxn=(R,R)-N,N'-双(亚水杨基)-1,2-二亚氨基环己烷]的二氯甲烷溶液ECD光谱的计算结果表明,可见区第一个ECD吸收带主要是π→d荷移跃迁(LMCT)所致,而不是通常认为的d-d跃迁:[Ni(sal-R,R-chxn)]的绝对构型为∧,其在可见区第一个ECD吸收带为正.将此ECD指纹应用于具有“闭壳层”电子结构的其它平面型手性[Ni(Salen)]和六配位trans-[CoⅢ(salen)L_2]络合物的绝对构型指认,具有一定的普适性.本文的研究结果对于深入理解手性[M(Salen)]络合物的配位立体化学、手征光学性质及其手性识别和不对称催化机理具有重要科学意义。
A correlation between the electronic circular dichroism (ECD) spectra and the absolute configurations of a serials' chiral salen-Ni(ll) complexes was investigated. The solid-state structures, absolute configurations, and preferential conformations in solution of quasi-planar chiral [Ni(salen)] complexes were studied using their crystal structures, solid-state and solution ECD spectra in combination with theoretical ECD calculations. Furthermore, two different nomenclatures for the absolute configurations of square-planar [M(salen)] complexes were inspected carefully, and suggestions for proper use of them are discussed. The calculated ECD spectra of [Ni(saI-R,R-chxn)] [saI-R,R-chxn = (R,R)-1,2-cyclohexylene bis(salicylicdeneiminate)] in dichloromethane solution revealed that the first ECD band in the visible region was dominated by the ligand- to-metal charge transfer transition (LMCT), which was incorrectly assigned to a d-d transition in the literature. When the absolute configuration of [Ni(saI-R,R-chxn)] was/k, the first ECD absorption band in the visible region was positive. This ECD fingerprint is universally applicable for assigning the absolute configurations of other square-planar chiral [Ni(salen)] and six-coordinate trans-[CoⅢ(salen)L2] complexes with a "closed-shell" electronic structure. This work provides some insight into the coordination stereochemistry and chiroptical properties of chiral [M(salen)] complexes. Additionally, this work is significant for the understanding of chira~ recognition and asymmetric catalytic mechanisms.