摘要：

In water and without using any ligand, palladium charcoal-catalyzed Suzuki coupling reaction of tetraarylborates with aryl bromides could be achieved in excellent yield. A concise mechanism consisting of four catalytic cycles is depicted in this paper. The Suzuki reaction has found a wide application in modern synthetic organic chemistry for the preparation of biaryl compounds. 1 Although, many efficient palla-dium catalysts with novel ligands have been discovered for the reaction, chemists have recently paid great atten-tion to the ligandless protocol catalyzed by palladium catalysts such as Pd(OAc) 2 or PdCl 2 . 2 With the advan-tage of its relatively inexpensive, stable, easily removable and reusable characteristics, palladium charcoal is the most suitable catalyst for this type of reaction in terms of green chemistry. Some excellent results of the cou-pling reactions of aryl halides/triflates with arylboronic acids catalyzed by Pd/C have been reported since 1994. 3 As a new type of borate source, sodium tetraphenyl-borate is a stable and commercially available reagent for the Suzuki reaction, and efforts to carry out the reac-tion with Pd(PPh 3) 4 or Pd(OAc) 2 have been published. 4 It has been discovered that its four phenyl groups can all be coupled with aryl halides to generate the product effi-ciently. 5 A reasonable mechanism for the reaction has not yet been reported, although a few attempts have been made. 4a All these findings inspired us to report our recent results for the study of the Pd/C-catalyzed, ligandless Suzuki reaction of sodium tetraarylborates in water.

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