Abstract
A water-soluble and air-stable Pd(NH3)2Cl2/cationic 2,2’-bipyridyl system was found to be a highly-efficient and reusable catalyst for the coupling of aryl iodides and alkenes in neat water using Bu3N as a base. The reaction was conducted at 140 °C in a sealed tube in air with a catalyst loading as low as 0.0001 mol % for the coupling of activated aryl iodides with butyl and ethyl acrylates, providing the corresponding products in good to excellent yields with very high turnover numbers. In the case of styrene, Mizoroki-Heck coupling products were obtained in good to high yields by using a greater catalyst loading (1 mol %) and TBAB as a phase-transfer agent. After extraction, the residual aqueous solution could be reused several times with only a slight decrease in its activity, making the Mizoroki-Heck reaction “greener”.
Highlights
Palladium-catalyzed coupling of aryl halides and alkenes, known as the Mizoroki-Heck reaction, is one of the most powerful processes available in organic synthesis for carbon–carbon bond formation [1,2]
As part of our continuing efforts in the development of green and reusable catalytic systems for carbon–carbon bond-forming reactions, we report the combination of Pd(NH3)2Cl2 and 1 to create a highly-efficient and reusable catalyst for the coupling of aryl iodides and alkenes in water under air, making the Mizoroki-Heck reaction green and economically viable (Scheme 1)
The catalytic system was prepared by mixing equimolar amounts of Pd(NH3)2Cl2 and 1 in water
Summary
Palladium-catalyzed coupling of aryl halides and alkenes, known as the Mizoroki-Heck reaction, is one of the most powerful processes available in organic synthesis for carbon–carbon bond formation [1,2]. This reaction is greatly facilitated in polar aprotic solvents such as DMA, DMF, DMSO, MeCN, and NMP under homogeneous catalysis The catalyst and organic products are often of similar solubility in organic solvents, and it is difficult to separate. The water-soluble catalytic system may be separated from the water-insoluble organic products by simple filtration or extraction, leading to the possibility of reuse of the catalyst. The development of a water-compatible and reusable catalytic system is highly attractive and valuable from the green chemistry and economics viewpoints
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