Metal-catalysed halogen exchange reactions of aryl halides

Abstract

Aryl halides are common synthetic targets themselves, and also highly versatile synthetic intermediates. Aryl chlorides are much more widely available and easier to synthesise than the other halide derivatives, so the development of effective methods for interconverting aryl halide derivatives would therefore be extremely useful. This article outlines which transformations are particularly desirable, and describes the progress that has been made on developing methods for carrying out those transformations using copper, nickel or palladium catalysts. The possible mechanisms of these reactions are discussed, with a view to identifying areas for future investigation.

Metformin as a versatile ligand for recyclable palladium-catalyzed cross-coupling reactions in neat water

“…In the Suzuki-Miyaura cross-coupling, aryl iodides are supposed to give higher yields than aryl the ratelimiting step is bromides. 41 As it is not the case here, this result suggests that the oxidative addition in the catalytic cycle, as initially postulated by Suzuki and Miyaura. 42 The water solubility of the substrates is also an important factor and aryl iodides are usually less soluble.…”

Bis(imino)acenaphthene (BIAN)-supported palladium(ii) carbene complexes as effective C–C coupling catalysts and solvent effects in organic and aqueous media

“…Consideration of the trend in activation energies for the aryl halides (C-Cl > C-Br > C-I; 407, 346, 280 kJ mol −1 , respectively) reveals that aryl chlorides are significantly the least reactive, yet they are industrially the most attractive because heavy halogenated by-products can be avoided. 29 In this study, appreciable yields of cross-coupled products were obtained using aryl chlorides at temperatures as low as 40°C.…”

Transition Metal-Mediated and Metal-Catalyzed Carbon–Fluorine Bond Formation

“…These limitations restrict the substrate scope to relatively simple arenes; additionally, the use of anhydrous fluoride salts can result in problematic side reactions due to the strong basicity of anhydrous fluoride [79,80,82]. The harsh conditions required for Halex-type fluorination reactions represent a significant kinetic barrier to C-F bond formation [83], but the nucleophilic fluorination of aryl halides is a thermodynamically favorable process [12]. Therefore, nucleophilic arene fluorination can conceptually be addressed by catalysis, and the search for suitable transition metal catalysts has been an area of highly active research in recent years.…”

“…The use of a transition metal catalyst or mediator can enable more selective arene fluorination, using milder conditions and less reactive electrophilic fluorinating reagents such as Selectfluor (F-TEDA-BF 4 ) [83,139], N-fluorobenzenesulfonimide (NFBS) [12,[140][141][142][143][144], and N-fluoropyridinium salts [3,[84][85][86][87][145][146][147][148][149][150]. Additionally, transition metal-mediated or metal-catalyzed electrophilic arene fluorination can occur through a range of mechanisms, including one-and two-electron pathways.…”