Sterckx Hans, De Houwer Johan, Mensch Carl, Caretti Ignacio, Tehrani Kourosch Abbaspour, Herrebout Wouter A, Van Doorslaer Sabine, Maes Bert U W
Department of Chemistry , University of Antwerp , Groenenborgerlaan 171 , B-2020 Antwerp , Belgium . Email:
Department of Physics , University of Antwerp , Universiteitsplein 1 , B-2610 Antwerp , Belgium.
Chem Sci. 2016 Jan 1;7(1):346-357. doi: 10.1039/c5sc03530a. Epub 2015 Sep 29.
A mechanistic study of the copper-catalyzed oxidation of the methylene group of aryl(di)azinylmethanes was performed. Initial reaction rates were measured making use of IR reaction monitoring and a kinetic analysis of the reaction was executed. The reaction proved to be first order in oxygen concentration. For substrate and acid concentration, saturation kinetics due to O mass transfer limitation were observed. The occurrence of mass transfer limitation was further confirmed by examining the effect of the stirring rate on the initial reaction rate. Interestingly, the effect of the concentration of the catalyst on the rate shows that higher loadings result in a maximal initial rate, followed initially by a steady decrease and subsequently a rate plateau when the concentration is increased further. Mass transfer limitation and increased concentration of dinuclear catalytically active species rationalizes this hitherto unprecedented rate behavior. Continuous-wave and pulsed electron paramagnetic resonance methods were used to characterize the catalytic species present in the solution during the reaction and confirmed the presence of both mono- and dinuclear copper species. Analysis of a diverse substrate scope points towards imine-enamine tautomerization as a crucial process in the oxidation reaction. DFT calculations of these equilibrium constants (p) provided us with a qualitative tool to predict whether or not a substrate is viable for oxidation under the reaction conditions developed.
对芳基（二）嗪基甲烷亚甲基的铜催化氧化进行了机理研究。利用红外反应监测测量了初始反应速率，并对该反应进行了动力学分析。该反应在氧气浓度方面为一级反应。对于底物和酸浓度，观察到由于氧传质限制导致的饱和动力学。通过考察搅拌速率对初始反应速率的影响，进一步证实了传质限制的存在。有趣的是，催化剂浓度对反应速率的影响表明，较高的负载量会导致最大初始速率，随后初始时稳定下降，当浓度进一步增加时出现速率平台期。传质限制和双核催化活性物种浓度的增加解释了这种前所未有的速率行为。采用连续波和脉冲电子顺磁共振方法对反应过程中溶液中存在的催化物种进行了表征，并证实了单核和双核铜物种的存在。对多种底物范围的分析表明，亚胺-烯胺互变异构是氧化反应中的一个关键过程。对这些平衡常数（p）的密度泛函理论计算为我们提供了一种定性工具，以预测底物在开发的反应条件下是否适合氧化。
