Zerk Timothy J, Moore Peter W, Harbort Joshua S, Chow Sharon, Byrne Lindsay, Koutsantonis George A, Harmer Jeffrey R, Martínez Manuel, Williams Craig M, Bernhardt Paul V
School of Chemistry and Molecular Biosciences , University of Queensland , Brisbane 4072 , Queensland , Australia . Email:
Centre for Advanced Imaging , University of Queensland , Brisbane 4072 , Australia.
Chem Sci. 2017 Dec 1;8(12):8435-8442. doi: 10.1039/c7sc04260d. Epub 2017 Oct 17.
The Ley-Griffith reaction is utilized extensively in the selective oxidation of alcohols to aldehydes or ketones. The central catalyst is commercially available tetra--propylammonium perruthenate (TPAP, -PrN[RuO]) which is used in combination with the co-oxidant -methylmorpholine -oxide (NMO). Although this reaction has been employed for more than 30 years, the mechanism remains unknown. Herein we report a comprehensive study of the oxidation of diphenylmethanol using the Ley-Griffith reagents to show that the rate determining step involves a single alcohol molecule, which is oxidised by a single perruthenate anion; NMO does not appear in rate law. A key finding of this study is that when pure -PrN[RuO] is employed in anhydrous solvent, alcohol oxidation initially proceeds very slowly. After this induction period, water produced by alcohol oxidation leads to partial formation of insoluble RuO, which dramatically accelerates catalysis a heterogeneous process. This is particularly relevant in a synthetic context where catalyst degradation is usually problematic. In this case a small amount of -PrN[RuO] must decompose to RuO to facilitate catalysis.
莱伊-格里菲斯反应在将醇选择性氧化为醛或酮的过程中得到了广泛应用。核心催化剂是市售的四丙基铵高钌酸盐（TPAP，PrN[RuO]），它与共氧化剂N-甲基吗啉-N-氧化物（NMO）联合使用。尽管该反应已被使用了30多年，但其机理仍然未知。在此，我们报告了一项使用莱伊-格里菲斯试剂对二苯甲醇氧化的全面研究，结果表明速率决定步骤涉及单个醇分子，该分子被单个高钌酸根阴离子氧化；NMO未出现在速率方程中。这项研究的一个关键发现是，当在无水溶剂中使用纯PrN[RuO]时，醇氧化最初进行得非常缓慢。在这个诱导期之后，醇氧化产生的水会导致部分不溶性RuO的形成，这极大地加速了催化过程——一个多相过程。这在合成环境中尤为重要，因为催化剂降解通常是个问题。在这种情况下，少量的PrN[RuO]必须分解为RuO以促进催化作用。
