Electronic Effect on Catalytic Water Oxidation by Single Site [Ru(QCl–tpy)(bpy)(OH₂)]²⁺ Catalyst

Abstract

The mononuclear [Ru(QCl-tpy)(bpy)(H 2 O)](PF 6 ) 2 was successfully synthesized and characterized by using several spectroscopic techniques (QCl-tpy = 2-4'-(2-chloroquinolin-3-yl)-2,2':6',2''-terpyridine). This complex shows only one pK a value at 10.2, due to the deprotonation from the bonded aqua ligand. This complex was successfully employed as a catalyst for chemical water oxidation in CF 3 SO 3 H solution (pH 1.0) by using Ce IV as an oxidant, shows initial turnover frequency (TOF) of 0.0014 s À1 .The manometry and electrochemical data shows that this complex is a better catalyst having turnover number (TON) 19 (out of 25) and overpotential of 600 mV. As compared to the parent Ru(tpy)(bpy)(H 2 O)](PF 6 ) 2 a higher catalytic effect was observed by complex 1, which is expected due to the cause of electronic effect dominating towards electron donating behavior.[a] J.

Effect of Quinoline Substitution on Water Oxidation by [Ru(Ql-tpy)(bpy)(OH2 )](PF6 )2

“…The resonance effect suggests that δ+ charge is delocalized over the carbon as well as the nitrogen atom of the quinoline moiety. This proposes that the quinoline moiety behaves as an electron withdrawing group (Scheme ) linked with the tpy backbone, leading to a lower catalytic effect by [Ru II (Ql‐tpy)(bpy)(H 2 O)] 2+ ( 1 ) as compared to the previously reported complex [Ru II (QCl‐tpy)(bpy)(OH 2 )] 2+ …”

“…Recently our group have reported the single site ruthenium complexes [Ru(2‐py‐tpy)(bpy)(OH 2 )](PF 6 ) 2 , [Ru(3‐py‐tpy)(bpy)(OH 2 )](PF 6 ) 2 , [Ru(4‐py‐tpy)(bpy)(OH 2 )](PF 6 ) 2 , and [Ru(QCl‐tpy)(bpy)(OH 2 )](PF 6 ) 2 , which are employed as successful chemical water oxidation catalysts in CF 3 SO 3 H acid solution at pH 1, in the presence of Ce IV as an oxidant . First three complexes [Ru(n‐py‐tpy)(bpy)(OH 2 )](PF 6 ) 2 (where n = 2 to 4), exhibit electron withdrawing nature due to the protonation at the free nitrogen atom in terminal pyridine moiety, in comparison to parent [Ru II (tpy)(bpy)(OH 2 )] 2+ complex.…”

Competent Electrocatalytic and Photocatalytic Proton Reduction by a Dechelated [Co(tpy)2]2+ Scaffold

“…Notably, from previous studies, the N atom in the QCl‐tpy ligand has a low p K a of 0.41, and it is protonated at pH 1.6 in phosphate buffer solution . The acid–base equilibrium studies (Figures S10–S13) reveal that the dechelation of one of the pyridine rings from a QCl‐tpy ligand occurs, with the generation of the [Co II (QCl‐tpy)(QCl‐tpyH)OH 2 ] 3+ species at pH 1.6, where QCl‐tpyH is the protonated form of the dechelated N atom of QCl‐tpy.…”

“…The ligand QCl‐tpy 2‐chloro‐3‐[2,6‐di(pyridin‐2‐yl)pyridine‐4‐yl]quinoline was synthesised by overnight refluxing of 2‐acetylpyridine (2 equiv.) with 2‐chloroquinoline‐3‐carbaldehyde in the presence of ammonia and KOH in an ethanolic medium, and a yellow precipitate was obtained . Subsequently, a methanolic solution containing QCl‐tpy (2 equiv.)…”

Systematic Influence of Electronic Modification of Ligands on the Catalytic Rate of Water Oxidation by a Single‐Site Ru‐Based Catalyst

“…[5][6][7][8][9] This functional aspect of the OEC may provide a possible path for the design of efficient catalysts for artificial photosynthesis. In the last decade, various water oxidation catalysts (WOCs) have been developed based on ruthenium, [10][11][12][13][14] manganese, [15][16][17][18][19] iron, [20][21][22][23] and iridium. [24][25][26][27] Integrated systems with chromophore-catalyst assemblies [28][29][30][31] and catalysts incorporated into metal-organic frameworks (MOF)s were also reported.…”