A Cu-free Sonogashira coupling was carried out in a microfluidic reactor with a static organic–aqueous interface and analyzed via in situ Raman spectroscopy. This was the first time that Raman spectroscopy was used in this way to analyze an active cross-coupling. This yielded a better understanding of the reactive interface-mainly that the Pd catalyst is only active in the mixture domain, either the cationic or the anionic deprotonation mechanism describes the reaction, and dissociation of the vinyl–Pd^II complex is potentially the rate determining step. The ratio of Pd to hydrophilic ligand is also non-stoichiometric as inactive stable Pd nanoparticles form. This validated previous kinetic models and the assumption that cross-couplings using a hydrophilic ligand can be described by thin film theory. Our findings support that the reaction should be performed with the minimal possible film thickness, which has implications on the design of the reactor. Characterization of the Pd and ligand within the interface is important for deriving accurate kinetic models that maximize catalyst recovery and selectivity while minimizing the environmental impacts of useful compounds when performing green chemistry.

中文翻译：

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Pd /亲水膦配体在水相无Cu Sonogashira偶联界面中的催化活性

在具有静态有机-水界面的微流体反应器中进行了无铜Sonogashira偶联，并通过原位拉曼光谱法进行了分析。这是拉曼光谱法首次用于分析有源交叉耦合。这使人们对反应界面有了更好的理解-主要是Pd催化剂仅在混合物域中具有活性，阳离子或阴离子去质子化机理描述了反应以及乙烯基-Pd ^II的解离复数可能是速率确定步骤。由于非活性的稳定的Pd纳米颗粒形式，Pd与亲水性配体的比例也是非化学计量的。这验证了先前的动力学模型，并假设可以通过薄膜理论描述使用亲水性配体的交叉偶联。我们的发现支持该反应应以尽可能小的膜厚度进行，这对反应器的设计有影响。界面中Pd和配体的表征对于获得精确的动力学模型非常重要，该模型可以最大程度地提高催化剂的回收率和选择性，同时在进行绿色化学反应时最大程度地减少有用化合物对环境的影响。