title: Noninnocent Proton-Responsive Ligand Facilitates Reductive Deprotonation and Hinders CO2 Reduction Catalysis in [Ru(tpy)(6DHBP)(NCCH3)](2+) (6DHBP = 6,6'-(OH)2bpy).
abstract: 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.
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973, United States.
authors.forename: Lele
authors.initials: L
authors.lastname: Duan
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973, United States.
authors.forename: Gerald F
authors.initials: GF
authors.lastname: Manbeck
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973, United States.
authors.forename: Marta
authors.initials: M
authors.lastname: Kowalczyk
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973, United States.|Department of Natural Science, Baruch College, CUNY , New York, New York 10010, United States.
authors.forename: David J
authors.initials: DJ
authors.lastname: Szalda
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973, United States.
authors.forename: James T
authors.initials: JT
authors.lastname: Muckerman
authors.affiliation: National Institute of Advanced Industrial Science and Technology , Tsukuba Central 5-1, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Himeda
authors.affiliation: Chemistry Department, Brookhaven National Laboratory , Upton, New York 11973, United States.
authors.forename: Etsuko
authors.initials: E
authors.lastname: Fujita