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Catalytic Four‐Electron Oxidation of Water by Intramolecular Coupling of the Oxo Ligands of a Bis(ruthenium–bipyridine) Complex
Author(s) -
Wada Tohru,
Ohtsu Hideki,
Tanaka Koji
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201102236
Subject(s) - ruthenium , chemistry , catalysis , electrolysis , redox , bipyridine , ion , electrochemistry , electron paramagnetic resonance , bulk electrolysis , intramolecular force , raman spectroscopy , medicinal chemistry , inorganic chemistry , stereochemistry , crystallography , cyclic voltammetry , electrode , nuclear magnetic resonance , organic chemistry , crystal structure , physics , optics , electrolyte
A bis(ruthenium–bipyridine) complex bridged by 1,8‐bis(2,2′:6′,2′′‐terpyrid‐4′‐yl)anthracene (btpyan), [Ru 2 (μ‐Cl)(bpy) 2 (btpyan)](BF 4 ) 3 ([ 1 ](BF 4 ) 3 ; bpy=2,2′‐bipyridine), was prepared. The cyclic voltammogram of [ 1 ](BF 4 ) 3 in water at pH 1.0 displayed two reversible [Ru II ,Ru II ] 3+ /[Ru II ,Ru III ] 4+ and [Ru II ,Ru III ] 4+ /[Ru III ,Ru III ] 5+ redox couples at E 1/2 (1)=+0.61 and E 1/2 (2)=+0.80 V (vs. Ag/AgCl), respectively, and an irreversible anodic peak at around E =+1.2 V followed by a strong anodic currents as a result of the oxidation of water. The controlled potential electrolysis of [ 1 ] 3+ ions at E =+1.60 V in water at pH 2.6 (buffered with H 3 PO 4 /NaH 2 PO 4 ) catalytically evolved dioxygen. Immediately after the electrolysis of the [ 1 ] 3+ ion in H 2 16 O at E =+1.40 V, the resultant solution displayed two resonance Raman bands at $\tilde \nu $ =442 and 824 cm ‐1 . These bands shifted to $\tilde \nu $ =426 and 780 cm −1 , respectively, when the same electrolysis was conducted in H 2 18 O. The chemical oxidation of the [ 1 ] 3+ ion by using a Ce IV species in H 2 16 O and H 2 18 O also exhibited the same resonance Raman spectra. The observed isotope frequency shifts (Δ $\tilde \nu $ =16 and 44 cm −1 ) fully fit the calculated ones based on the RuO and OO stretching modes, respectively. The first successful identification of the metalOOmetal stretching band in the oxidation of water indicates that the oxygen–oxygen bond at the stage prior to the evolution of O 2 is formed through the intramolecular coupling of two Ru–oxo groups derived from the [ 1 ] 3+ ion.