N-(3-Chloro-2-quinoxalinyl)-N'-arylimidazolium salts (aryl = 2,6-diisopropylphenyl [HL1Cl]Cl, aryl = mesityl [HL2Cl]Cl) have been synthesized by treating 2,3-dichloroquinoxaline with the corresponding N'-arylimidazole in neat water. Facile reactions of these imidazolium salts with Pd(PPh) and Pd(dba)/PPh (dba = dibenzyledene acetone) at 50 °C have afforded zwitterionic palladium(ii) complexes [Pd(HL1)(PPh)Cl] (I) and [Pd(HL2)(PPh)Cl] (II) in excellent yields. I and II have been tested for their ability to catalyze Suzuki-Miyaura cross coupling (SMC) reactions in neat water/KCO and are found to be highly active for carrying out these reactions between aryl bromides and organoboron reagents. Furthermore, the scope of the catalyst I was also examined by employing (hetero)aryl bromides, hydrophilic aryl bromides, benzyl bromides and various organoboron reagents. More than 80 aryl/benzyl bromide-arylboronic acid combinations were screened in neat water/KCO and it was found that I was a versatile catalyst, which produced biaryls/diarylmethanes in excellent yields. A TON of 82 000 was achieved by using I. Studies on the mechanism have also been carried out to investigate the involvement of carbene complexes in the catalytic path. Poison tests and a two-phase test were also conducted and the results are reported.
The Suzuki–Miyaura cross‐coupling (SMC) reactions of several heteroaryl chlorides, benzyl chlorides, and aryl acid chlorides with (hetero)arylboron reagents have been investigated in the presence of [Pd(HL1)(PPh3)Cl2] (I) [HL1 = 3‐[(2,6‐diisopropylphenyl)‐1‐imidazolio]‐2‐quinoxalinide] as catalyst and K2CO3 as base in neat water. The synthesis of the heterocycle‐containing biaryls required the addition of 2 mol‐% of a phosphine ligand (PPh3 or X‐Phos). A combination of more than 115 substrates were screened and it was found that I is a versatile catalyst that can produce heterocycle‐containing biaryls, diarylmethanes, and benzophenones in moderate‐to‐excellent yields.
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