A novel non-C2-symmetric bis-benzimidazolium salt derived from (±)-valinol has been prepared by a simple and straightforward process in good yield. The structure of bis-benzimidazolium salt provided a bulky steric group on the ethylene bridge; which facilitates the catalytic efficacy in the C(sp2)–C(sp2) formation. Its catalytic activity in Suzuki–Miyaura cross-coupling reaction of unactivated aryl chlorides has been found to have high efficacy in 1 mol% Pd loading. This protocol demonstrated the potential on the synthesis of sterically hindered biaryls.
A new class of indolyl-based benzimidazolium salts has first been obtained by a simple process from commercially available indole, 4-iodoanisole, and benzimidazole. The structure of these salts offers beneficial features which include the high potential of steric and electronic tunability on the indole moiety and that of steric effect on the wingtip of benzimidazole moiety. The combination of indolyl-based benzimidazolium salts and palladium metal precursors formed in situ are high-efficient catalysts for accessing a wide range of biaryls in good to excellent yields, in particular, diortho-substituted biaryls, as well as good functional group tolerance, and the catalyst loading down to 0.25 mol % of Pd can be achieved.
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