Structure and pulsed EPR characterization of N,N′-bis(5-tert-butylsalicylidene)-1,2-cyclohexanediamino-vanadium(iv) oxide and its adducts with propylene oxide
作者:E. Carter、I. A. Fallis、B. M. Kariuki、I. R. Morgan、D. M. Murphy、T. Tatchell、S. Van Doorslaer、E. Vinck
DOI:10.1039/c1dt10378d
日期:——
The role of steric hindrance in controlling the binding mode of propylene oxide to a novel vanadyl salen-type complex N,Nâ²-bis(5-tert-butylsalicylidene)-1,2-cyclohexanediamino-vanadium(IV) oxide, [VO(3)], has been investigated using CW/pulse EPR, ENDOR and HYSCORE spectroscopy and compared to that of the parent complex N,Nâ²-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamino-vanadium(IV) oxide, [VO(1)]. The single-crystal X-ray structure of [VO(3)]·HCCl3 has been determined by X-ray analysis and is complemented by DFT calculations and circular dichroism measurements. The structure of the complex in frozen solution, as revealed by the EPR methods, is in good agreement with the X-ray and DFT analyses. Removal of the âinnerâ tert-butyl groups from the salicylidene rings reduces the steric hindrance between the ligand and epoxide substrate. As a result the selectivity for binding single enantiomers of propylene oxide in these complexes is reversed in [VO(3)] relative to [VO(1)].
利用 CW/脉冲 EPR、ENDOR 和 HYSCORE 光谱研究了立体阻碍在控制环氧丙烷与 N,Nâ²-双(5-叔丁基水杨基)-1,2-环己烷二氨基氧化钒(IV)新型络合物[VO(3)]的结合模式中的作用、使用 CW/脉冲 EPR、ENDOR 和 HYSCORE 光谱进行了研究,并与母体复合物 N,Nâ²-双(3,5-二叔丁基水杨酰)-1,2-环己烷二氨基氧化钒(IV)[VO(1)]的光谱进行了比较。通过 X 射线分析确定了[VO(3)]Â-HCl3 的单晶 X 射线结构,并辅以 DFT 计算和圆二色性测量。EPR 方法揭示的该复合物在冷冻溶液中的结构与 X 射线和 DFT 分析结果十分吻合。从水杨醛环中去除âinnerâ叔丁基可以减少配体与环氧化物底物之间的立体阻碍。因此,[VO(3)]与[VO(1)]复合物结合环氧丙烷单对映体的选择性发生了逆转。