Glasnov Toma N, Findenig Silvia, Kappe C Oliver
Christian Doppler Laboratory for Microwave Chemistry (CDLMC) and Institute of Chemistry, Karl-Franzens-University Graz, Heinrichstrasse 28, 8010 Graz, Austria.
Chemistry. 2009;15(4):1001-10. doi: 10.1002/chem.200802200.
Mizoroki-Heck couplings of aryl iodides and bromides with butyl acrylate were investigated as model systems to perform transition-metal-catalyzed transformations in continuous-flow mode. As a suitable ligandless catalyst system for the Mizoroki-Heck couplings both heterogeneous and homogeneous Pd catalysts (Pd/C and Pd acetate) were considered. In batch mode, full conversion with excellent selectivity for coupling was achieved applying high-temperature microwave conditions with Pd levels as low as 10(-3) mol %. In continuous-flow mode with Pd/C as a catalyst, significant Pd leaching from the heterogeneous catalyst was observed as these Mizoroki-Heck couplings proceed by a homogeneous mechanism involving soluble Pd colloids/nanoparticles. By applying low levels of Pd acetate as homogeneous Pd precatalyst, successful continuous-flow Mizoroki-Heck transformations were performed in a high-temperature/pressure flow reactor. For both aryl iodides and bromides, high isolated product yields of the cinnamic esters were obtained. Mechanistic issues involving the Pd-catalyzed Mizoroki-Heck reactions are discussed.
研究了芳基碘化物和溴化物与丙烯酸丁酯的Mizoroki-Heck偶联反应，作为在连续流动模式下进行过渡金属催化转化的模型体系。作为适用于Mizoroki-Heck偶联反应的无配体催化剂体系，考虑了非均相和均相钯催化剂（Pd/C和醋酸钯）。在间歇模式下，在高温微波条件下，钯含量低至10(-3) mol%时，实现了完全转化且偶联选择性优异。在以Pd/C为催化剂的连续流动模式下，由于这些Mizoroki-Heck偶联反应通过涉及可溶性钯胶体/纳米颗粒的均相机制进行，观察到非均相催化剂有大量钯浸出。通过使用低水平的醋酸钯作为均相钯预催化剂，在高温/高压流动反应器中成功进行了连续流动的Mizoroki-Heck转化反应。对于芳基碘化物和溴化物，均获得了肉桂酸酯的高分离产率。讨论了涉及钯催化的Mizoroki-Heck反应的机理问题。
