Seok Won K, Meyer Thomas J
Department of Chemistry, Dongguk University, 26 Pil-Dong, Chung-Ku, Seoul 100-715, Korea.
Inorg Chem. 2005 May 30;44(11):3931-41. doi: 10.1021/ic040119z.
The oxidation of benzaldehyde and several of its derivatives to their carboxylic acids by cis-[Ru(IV)(bpy)2(py)(O)]2+ (Ru(IV)=O2+; bpy is 2,2'-bipyridine, py is pyridine), cis-[Ru(III)(bpy)2(py)(OH)]2+ (Ru(III)-OH2+), and [Ru(IV)(tpy)(bpy)(O)]2+ (tpy is 2,2':6',2''-terpyridine) in acetonitrile and water has been investigated using a variety of techniques. Several lines of evidence support a one-electron hydrogen-atom transfer (HAT) mechanism for the redox step in the oxidation of benzaldehyde. They include (i) moderate k(C-H)/k(C-D) kinetic isotope effects of 8.1 +/- 0.3 in CH3CN, 9.4 +/- 0.4 in H2O, and 7.2 +/- 0.8 in D2O; (ii) a low k(H2O/D2O) kinetic isotope effect of 1.2 +/- 0.1; (iii) a decrease in rate constant by a factor of only approximately 5 in CH3CN and approximately 8 in H2O for the oxidation of benzaldehyde by cis-[Ru(III)(bpy)2(py)(OH)]2+ compared to cis-[Ru(IV)(bpy)2(py)(O)]2+; (iv) the appearance of cis-[Ru(III)(bpy)2(py)(OH)]2+ rather than cis-[Ru(II)(bpy)2(py)(OH2)]2+ as the initial product; and (v) the small rho value of -0.65 +/- 0.03 in a Hammett plot of log k vs sigma in the oxidation of a series of aldehydes. A mechanism is proposed for the process occurring in the absence of O2 involving (i) preassociation of the reactants, (ii) H-atom transfer to Ru(IV)=O2+ to give Ru(III)-OH2+ and PhCO, (iii) capture of PhCO by Ru(III)-OH2+ to give Ru(II)-OC(O)Ph+ and H+, and (iv) solvolysis to give cis-[Ru(II)(bpy)2(py)(NCCH3)]2+ or the aqua complex and the carboxylic acid as products.
已使用多种技术研究了顺式-[Ru(IV)(bpy)₂(py)(O)]²⁺（Ru(IV)=O²⁺；bpy为2,2'-联吡啶，py为吡啶）、顺式-[Ru(III)(bpy)₂(py)(OH)]²⁺（Ru(III)-OH²⁺）和[Ru(IV)(tpy)(bpy)(O)]²⁺（tpy为2,2':6',2''-三联吡啶）在乙腈和水中将苯甲醛及其几种衍生物氧化为羧酸的反应。几条证据支持苯甲醛氧化中氧化还原步骤的单电子氢原子转移（HAT）机制。这些证据包括：(i) 在CH₃CN中k(C-H)/k(C-D)动力学同位素效应适中，为8.1±0.3，在H₂O中为9.4±0.4，在D₂O中为7.2±0.8；(ii) k(H₂O/D₂O)动力学同位素效应较低，为1.2±0.1；(iii) 与顺式-[Ru(IV)(bpy)₂(py)(O)]²⁺相比，顺式-[Ru(III)(bpy)₂(py)(OH)]²⁺氧化苯甲醛时，速率常数在CH₃CN中仅降低约5倍，在H₂O中降低约8倍；(iv) 初始产物是顺式-[Ru(III)(bpy)₂(py)(OH)]²⁺而非顺式-[Ru(II)(bpy)₂(py)(OH₂)]²⁺；(v) 在一系列醛氧化的log k对σ的哈米特图中，ρ值较小，为-0.65±0.03。提出了在不存在O₂时发生的过程的机制，包括：(i) 反应物的预缔合；(ii) 氢原子转移至Ru(IV)=O²⁺生成Ru(III)-OH²⁺和PhCO；(iii) Ru(III)-OH²⁺捕获PhCO生成Ru(II)-OC(O)Ph⁺和H⁺；(iv) 溶剂解生成顺式-[Ru(II)(bpy)₂(py)(NCCH₃)]²⁺或水合配合物以及羧酸作为产物。
