Strong Impact of Intramolecular Hydrogen Bonding on the Cathodic Path of [Re(3,3′-dihydroxy-2,2′-bipyridine)(CO)3Cl] and Catalytic Reduction of Carbon Dioxide
Strong Impact of Intramolecular Hydrogen Bonding on the Cathodic Path of [Re(3,3′-dihydroxy-2,2′-bipyridine)(CO)3Cl] and Catalytic Reduction of Carbon Dioxide
复制标题
分子内氢键对[Re(3,3-二羟基-2,2-联吡啶)(CO)3Cl]阴极路径的强烈影响和二氧化碳的催化还原
作者：
James O. Taylor;G. Neri;Liam Banerji;Alexander J. Cowan;F. Hartl
本文提出了7族金属配合物[Re(3,3 ' -DHBPY)(CO)3Cl] （3,3 ' -DHBPY = 3,3 ' -二羟基-2,2 ' -联吡啶）的阴极路径，产生了一种电化学还原CO2为CO的中活性催化剂。循环伏安法和IR/ UV-vis光谱电化学相结合的技术发现，与之前发表的Re/4,4 ' -DHBPY同族物相比，电化学还原的母体配合物的化学性质存在显着差异。弱配位THF的初始不可逆阴极步骤转向负电极电位小得多，反映了一个羟基的易还原去质子化和强的分子内氢键O - h···O -。后一过程在碱性二甲基甲酰胺中自发发生，Re/4,4 ' -DHBPY保持稳定。在环境条件下，单去质子化[Re(3,3 ' -DHBPY-H+)(CO)3Cl]−的后续还原发生在接近Re/4,4 ' -DHBPY-H+衍生物的阴极电位下。然而，对于稳定的3,3 ' -DHBPY-H+配体，第二个阴极波的后一个过程更为复杂，涉及三个电子的总体转移。快速电位阶跃电解诱导第二个O-H键的1e -还原裂解，触发Cl -配体与[Re(3,3 ' - dhbpy - 2h +)(CO)3Cl]2 -的解离。THF中第二个阴极步骤的最终产物被确定为5坐标[Re(3,3 ' - dhbpy - 2h +)(CO)3]3 -，相当于经典的2e -还原[Re(BPY)(CO)3]−。DHBPY配体的每一次还原去质子化导致三羰基配合物的IR ν(CO)吸收红移约10 cm-1，便于根据文献数据比较相应的Re/BPY配合物的产物分配。在强配位丁腈中证实了[Re(3,3 ' - dhbpy - 2h +)(CO)3Cl]2 -的Cl -解离。后一种离子在223 K时稳定，在258 K时转化为六坐标[Re(3,3 ' - dhbpy - 2h +)(CO)3(PrCN)]3 -。取代的母体[Re(3,3 ' -DHBPY)(CO)3(PrCN)]+也通过初始还原顺利地去质子化为[Re(3,3 ' -DHBPY- h +)(CO)3(PrCN)]，获得了有用的参考数据。后一种配合物最终在第二阴极波处转化为[Re(3,3 ' - dhbpy - 2h +)(CO)3(PrCN)]3 -，通过反直觉的ETC步骤生成母体配合物的1e -自由基，即[Re(3,3 ' - dhbpy)(CO)3(PrCN)]。在第二阴极波开始时，同样的还原路径还遵循[Re(3,3 ' - dhbpy - h +)(CO)3Cl]−，其中ETC步骤导致中间产物[Re(3,3 ' - dhbpy)(CO)3Cl]•-进一步还原为[Re(3,3 ' - dhbpy - 2h +)(CO)3]3 -作为CO2催化剂。
Herein, we present the cathodic paths of the Group-7 metal complex [Re(3,3′-DHBPY)(CO)3Cl] (3,3′-DHBPY = 3,3′-dihydroxy-2,2′-bipyridine) producing a moderately active catalyst of electrochemical reduction of CO2 to CO. The combined techniques of cyclic voltammetry and IR/UV–vis spectroelectrochemistry have revealed significant differences in the chemistry of the electrochemically reduced parent complex compared to the previously published Re/4,4′-DHBPY congener. The initial irreversible cathodic step in weakly coordinating THF is shifted toward much less negative electrode potentials, reflecting facile reductive deprotonation of one hydroxyl group and strong intramolecular hydrogen bonding, O–H···O–. The latter process occurs spontaneously in basic dimethylformamide where Re/4,4′-DHBPY remains stable. The subsequent reduction of singly deprotonated [Re(3,3′-DHBPY-H+)(CO)3Cl]− under ambient conditions occurs at a cathodic potential close to that of the Re/4,4′-DHBPY-H+ derivative. However, for the stabilized 3,3′-DHBPY-H+ ligand, the latter process at the second cathodic wave is more complex and involves an overall transfer of three electrons. Rapid potential step electrolysis induces 1e–-reductive cleavage of the second O–H bond, triggering dissociation of the Cl– ligand from [Re(3,3′-DHBPY-2H+)(CO)3Cl]2–. The ultimate product of the second cathodic step in THF was identified as 5-coordinate [Re(3,3′-DHBPY-2H+)(CO)3]3–, the equivalent of classical 2e–-reduced [Re(BPY)(CO)3]−. Each reductive deprotonation of the DHBPY ligand results in a redshift of the IR ν(CO) absorption of the tricarbonyl complexes by ca. 10 cm–1, facilitating the product assignment based on comparison with the literature data for corresponding Re/BPY complexes. The Cl– dissociation from [Re(3,3′-DHBPY-2H+)(CO)3Cl]2– was proven in strongly coordinating butyronitrile. The latter dianion is stable at 223 K, converting at 258 K to 6-coordinate [Re(3,3′-DHBPY-2H+)(CO)3(PrCN)]3–. Useful reference data were obtained with substituted parent [Re(3,3′-DHBPY)(CO)3(PrCN)]+ that also smoothly deprotonates by the initial reduction to [Re(3,3′-DHBPY-H+)(CO)3(PrCN)]. The latter complex ultimately converts at the second cathodic wave to [Re(3,3′-DHBPY-2H+)(CO)3(PrCN)]3– via a counterintuitive ETC step generating the 1e– radical of the parent complex, viz., [Re(3,3′-DHBPY)(CO)3(PrCN)]. The same alternative reduction path is also followed by [Re(3,3′-DHBPY-H+)(CO)3Cl]− at the onset of the second cathodic wave, where the ETC step results in the intermediate [Re(3,3′-DHBPY)(CO)3Cl]•– further reducible to [Re(3,3′-DHBPY-2H+)(CO)3]3– as the CO2 catalyst.
影响因子：
37.8
作者：
Neri, Gaia;Walsh, James. J.;Cowan, Alexander J.
通讯作者：
Cowan, Alexander J.
具有质子响应配体的双核铼络合物作为电化学 CO2 还原的氧化还原催化剂
影响因子：
4.6
作者：
A. Wilting;T. Stolper;R. A. Mata;I. Siewert
通讯作者：
I. Siewert