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Intermediates in the Oxidative Degradation of a Ruthenium‐Bound 2,2′‐Bipyridyl–Phenoxy Ligand during Catalytic Water Oxidation
Author(s) -
Liu Yingying,
Chen Gui,
Yiu ShekMan,
Wong ChunYuen,
Lau TaiChu
Publication year - 2018
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201701319
Subject(s) - ruthenium , chemistry , ligand (biochemistry) , catalysis , medicinal chemistry , aqueous solution , bipyridine , photochemistry , benzoquinone , redox , inorganic chemistry , organic chemistry , crystal structure , receptor , biochemistry
Water‐oxidation catalysts (WOCs) based on transition‐metal complexes often undergo oxidative degradation of the ligands, which leads to unidentifiable products. We report herein the use of a ruthenium(III) complex bearing a 2,2′‐bipyridyl (bpy)–bis(phenoxy) ligand, [Ru(L)(pic) 2 ] + [ 1 , H 2 L=6,6′‐bis(2‐hydroxyphenyl)‐2,2′‐bipyridine, pic=4‐picoline] as a WOC. The phenoxy‐type ligand in 1 is readily oxidized by Ce IV in aqueous acidic medium to give a ruthenium bpy–dicarboxylate complex ([Ru(bda)(pic) 2 ] + , H 2 bda=2,2′‐bipyridine‐6,6′‐dicarboxylic acid) via ruthenium bpy–phenoxybenzoquinone ( 1′ ) and ruthenium bpy–bis(benzoquinone) ( 1′′ ) intermediates. All four ruthenium species can oxidize water; however, 1 and 1′ are rapidly oxidized to 1′′ by Ce IV . On the other hand, 1′′ is robust enough that it is responsible for the initial phase of O 2 evolution before it is finally oxidized to CO 2 and [Ru(bda)(pic) 2 ] + , which is a highly active WOC.