Design and synthesis of thioether-imidazolium chlorides as efficient ligands for palladium-catalyzed Suzuki–Miyaura coupling of aryl bromides with arylboronic acids

Sulfur-functionalized N-heterocyclic carbenes and their transition metal complexes

“…S-NHC palladium complexes with ligand precursors 22a and 22b showed the highest activity towards Suzuki-Miyaura coupling reactions of substituted bromobenzenes and substituted phenyl boronic acids with excellent isolated yields of the desired biaryl products [24]. These reaction conditions also provided excellent yields for the C-C coupling of bromo-N-heterocyclic compounds with substituted phenyl boronic acids [24]. The new S-NHC ligands were further evaluated in other catalytic transformations as outlined in Scheme 5 [41,42].…”

“…Kuriyama et al [24] reported the first aryl thioether-tethered imidazolinium salt synthesis (22 and 23) from S-alkylated ortho-aminothiophenols (15a-c), and mesityl and 2,6-diisopropyl anilinyloxamic acids (16 and 17) as outlined in Scheme 4. The threestep pathway involves the formation of the N,N -disubstituted oxalamides (18 and 19) by the reaction of oxamic acids with 1,3-dicyclohexylcarbodiimide (DCC) and 1-hydroxybenzotriazole (HOBT), or alternatively with oxalic chloride and catalytic amounts of DMF followed by treatment with triethyl amine.…”

“…Bromination to 28 is accomplished by reaction with phosphorus tribromide. The imidazolium salts (24) and benzimidazolium salts (25) are obtained by the N-alkylation reaction of 1-methylimidazole and 1-methylbenzimidazole, respectively, in overall isolated yields from 26 of 57-64%. The resulting palladium complexes were obtained by treatment of 24 [57] and 25 [25] with silver oxide in dichloromethane to generate the corresponding NHC-Ag complex (29), which was reacted without isolation with cis-palladium diacetonitriledibromide (0.5-1 equiv.)…”

“…Compared to other donor-functionalized NHCs, the usage of S-NHC complexes is in its infancy. Their versatility has however been demonstrated in catalytic transformations such as Suzuki-Miyaura [24][25][26][27][28][29], Mizoroki-Heck [30], Sonogashira [29], ethylene polymerization [31], aryl amination [32], hydrogenation [33,34], hydrosilylation [35,36], allylic substitution [37,38], asymmetric 1,3-cylcoaddition of imino glycinates [39], asymmetric 1,4 addition of ␥-keto esters [40] as well as the palladium-catalyzed 1,2-addition of aldehydes with boronic acids [41] and trifluoroborates [42]. The intent of this review is to provide a comprehensive review on sulfur-functionalized NHCs and their transition metal complexes by categorization according to sulfur functionalities.…”

Palladium-imidazolinium carbene-catalyzed arylation of aldehydes with arylboronic acids in water

“…12 In the course of our investigation on the palladium-catalyzed 1,2-addition of organoboron reagents with N-heterocyclic carbene precursors 1, 13 we found the palladium/thioetherimidazolinium chloride system had the ability to tolerate water and achieved high catalyst performance even in the arylation of aldehydes using arylboronic acids in only water without further assistance such as co-solvents, surfactants, and hydrophilic auxiliaries. Herein, we would like to describe the full details on this investigation.…”