Noninnocent Proton-Responsive Ligand Facilitates Reductive Deprotonation and Hinders CO2 Reduction Catalysis in [Ru(tpy)(6DHBP)(NCCH3)]2+ (6DHBP = 6,6′-(OH)2bpy)

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• 作者：Lele Duan ; Gerald F. Manbeck ; Marta Kowalczyk ; David J. Szalda ; James T. Muckerman ; Yuichiro Himeda ; Etsuko Fujita
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：May 2, 2016
• 年：2016
• 卷：55
• 期：9
• 页码：4582-4594
• 全文大小：747K
• 年卷期：0
• ISSN：1520-510X

文摘

Ruthenium complexes with proton-responsive ligands [Ru(tpy)(nDHBP)(NCCH₃)](CF₃SO₃)₂ (tpy = 2,2′:6′,2″-terpyridine; nDHBP = n,n′-dihydroxy-2,2′-bipyridine, n = 4 or 6) were examined for reductive chemistry and as catalysts for CO₂ reduction. Electrochemical reduction of [Ru(tpy)(nDHBP)(NCCH₃)]²⁺ generates deprotonated species through interligand electron transfer in which the initially formed tpy radical anion reacts with a proton source to produce singly and doubly deprotonated complexes that are identical to those obtained by base titration. A third reduction (i.e., reduction of [Ru(tpy)(nDHBP–2H⁺)]⁰) triggers catalysis of CO₂ reduction; however, the catalytic efficiency is strikingly lower than that of unsubstituted [Ru(tpy)(bpy)(NCCH₃)]²⁺ (bpy = 2,2′-bipyridine). Cyclic voltammetry, bulk electrolysis, and spectroelectrochemical infrared experiments suggest the reactivity of CO₂ at both the Ru center and the deprotonated quinone-type ligand. The Ru carbonyl formed by the intermediacy of a metallocarboxylic acid is stable against reduction, and mass spectrometry analysis of this product indicates the presence of two carbonates formed by the reaction of DHBP–2H⁺ with CO₂.