Rotundo Laura, Polyansky Dmitry E, Gobetto Roberto, Grills David C, Fujita Etsuko, Nervi Carlo, Manbeck Gerald F
Chemistry Department, University of Torino, Via P. Giuria 7, 10125 Torino, Italy.
CIRCC (Bari), University of Bari, Via Celso Ulpiani 27, 70126 Bari, Italy.
Inorg Chem. 2020 Sep 8;59(17):12187-12199. doi: 10.1021/acs.inorgchem.0c01181. Epub 2020 Aug 17.
A new Re bipyridine-type complex, namely, -Re(pmbpy)(CO)Cl (pmbpy = 4-phenyl-6-(2-hydroxy-phenyl)-2,2'-bipyridine), , carrying a single OH moiety as local proton source, has been synthesized, and its electrochemical behavior under Ar and under CO has been characterized. Two isomers of , namely, characterized by the proximity of Cl to OH and , are identified. The interconversion between and is clarified by DFT calculations, which reveal two transition states. The energetically lower pathway displays a non-negligible barrier of 75.5 kJ mol. The 1e electrochemical reduction of affords the neutral intermediate , formally derived by reductive deprotonation and loss of Cl from . , which exhibits an entropically favored intramolecular Re-O bond, has been isolated and characterized. The detailed electrochemical mechanism is demonstrated by combined chemical reactivity, spectroelectrochemistry, spectroscopic (IR and NMR), and computational (DFT) approaches. Comparison with previous Re and Mn derivatives carrying local proton sources highlights that the catalytic activity of Re complexes is more sensitive to the presence of local OH groups. Similar to (2OH = 4-phenyl-6-(phenyl-2,6-diol)-2,2'-bipyridine), and display a selective reduction of CO to CO. In the case of the Re bipyridine-type complex, the formation of a relatively stable Re-O bond and a preference for phenolate-based reactivity with CO slightly inhibit the electrocatalytic reduction of CO to CO, resulting in a low TON value of 9, even in the presence of phenol as a proton source.
一种新型的铼联吡啶型配合物，即 -Re(pmbpy)(CO)Cl（pmbpy = 4-苯基-6-(2-羟基-苯基)-2,2'-联吡啶）已被合成，该配合物带有单个OH基团作为局部质子源，并对其在氩气和一氧化碳氛围下的电化学行为进行了表征。确定了 的两种异构体，即 ，其特征在于Cl与OH的接近程度不同。通过DFT计算阐明了 和 之间的相互转化，计算结果揭示了两个过渡态。能量较低的途径显示出75.5 kJ/mol的不可忽略的势垒。 的单电子电化学还原产生中性中间体 ，它是通过 的还原去质子化和Cl的损失而正式衍生出来的。 已被分离和表征，它表现出熵有利的分子内Re-O键。通过化学反应性、光谱电化学、光谱（红外和核磁共振）以及计算（DFT）方法相结合，证明了详细的电化学机理。与先前带有局部质子源的铼和锰衍生物的比较突出表明，铼配合物的催化活性对局部OH基团的存在更为敏感。与 (2OH = 4-苯基-6-(苯基-2,6-二醇)-2,2'-联吡啶)类似， 和 显示出将CO选择性还原为CO。对于铼联吡啶型配合物，相对稳定的Re-O键的形成以及对基于酚盐与CO反应性的偏好，即使在存在苯酚作为质子源的情况下，也会略微抑制CO电催化还原为CO，导致TON值低至9。
