Kinetics of oxidation of quinol and ascorbic acid with the phen substituted semiquinone ligand, (5,6-dioxolene-1,10-phenanthroline-O,O), bound to the RuII(bipy)2 moiety
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- 作者：Amit Mondal ; Piyali De ; Subrata Mukhopadhyay ; Rupendranath Banerjee ; Prasenjit Kar ; Amilan D. Jose ; Amitava Das
- 关键词：Kinetics ; Radicals ; Phenanthrolinesemiquinone ; Ascorbic acid ; Quinol ; Bipyridine
- 刊名：Polyhedron
- 出版年：2009
- 出版时间：2 September 2009
- 年：2009
- 卷：28
- 期：13
- 页码：2655-2660
- 全文大小：306 K
文摘
In 10 % (v/v) CH3CN–H2O media, the parent complex [Ru(bpy)2(sqphen)]+ (I+) coexists with its conjugate acid [Ru(bpy)2(sqphenH)]2+ (HI2+): HI2+ H+ + I+; (deprotonation constant, = 0.01; (bpy = 2,2′-bipyridine; sqphen = 5,6-dioxolene-1,10-phenanthroline-O,O). Electrochemical reduction, and also chemical reductions with quinol and ascorbic acid, produced the corresponding catechol complex [Ru(bpy)2(catphen)] (IR), which also in solution coexists with its conjugate acid, [Ru(bpy)2(catphenH)]+ () (deprotonation constant, = 0.002). Progressive increase in [ascorbic acid] led to rate saturation, indicating adduct formation (formation constant, Q = 990 ± 80 M−1). Added H+, and also redox-innocent Lewis acid Zn2+, increased E1/2 but decreased the chemical reduction rates. Only an insignificant solvent isotope effect (kH2O/kD2O) was noted. An increased percentage of CH3CN in the solvent also retards the rate. [Ru(bpy)2(sqphen)]+ (I+) reacts at a much slower rate than [Ru(bpy)2sq]+ (sq = the unsubstituted semiquinone). Phen in the substituted ligand sqphen is known to become a much weaker base (sqphen < phen); O,O-coordination to the RuII(bpy) center further lowers the basicity of sqphen. Catphen (O,O) in IR, produced on reduction of I+, is a stronger base than the O,O-coordinated sqphen in I+.