Taming Nickel-Catalyzed Suzuki-Miyaura Coupling: A Mechanistic Focus on Boron-to-Nickel Transmetalation

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Taming Nickel-Catalyzed Suzuki-Miyaura Coupling: A Mechanistic Focus on Boron-to-Nickel Transmetalation, ACS Catal. 2018, 8, 4812−4823

 

The palladium-catalyzed Suzuki-Miyaura (S-M) cross-coupling, involving an organoboron reagent and an organic halide (or pseudohalide), is one of the most widely used reactions for the formation of C−C bonds. This transformation tolerates a broad range of experimental conditions, as it proceeds well with a large array of catalysts, bases, and solvents. Thanks to the reliability of existing experimental protocols, this reaction has entered the standard organic chemists’ toolbox. Its mechanism has been investigated both experimentally and theoretically.

 

Over the past decade, the supremacy of palladium complexes as catalysts for the S-M reaction has been challenged by the development of several nickel-based protocols. Nickel catalysts are not only cheaper than palladium-based ones, but they are also able to activate less reactive electrophiles, such as aryl chlorides,  sulfonate esters, nitriles, ammonium salts, ethers, acetals, esters, amides, fluorides, sulfamates, and carbamates, without the need of expensive ligands.

 

 

Despite these undeniable advantages, the nickel-catalyzed SM coupling is still much less used in practical synthesis than the Pd-catalyzed version, probably due to its reputation of erratic performances. Indeed, Ni-catalyzed S-M reactions generally require high catalyst loading (3− 10 mol %), and they are quite sensitive to the reaction conditions. The choice of the base/solvent combination is crucial: in most cases either THF, dioxane, or toluene must be used in conjunction with scarcely soluble inorganic bases, such as K3PO4or K2CO3. Conversely, alkali hydroxides and excessive amounts of water seem to deactivate nickel catalysts. To the best of our knowledge, the reasons for this behavior are still unknown.

 

Pour plus d'information, consultez le communiqué de presse associé à cet article : Rationaliser une catalyse au nickel entre théorie et expérience !

 

 

Résumé: 

ACS Catal. 2018, 8, 4812−4823

 

The mechanism of boron-to-nickel transmetalation, the key step of the nickel-catalyzed Suzuki-Miyaura (SM) coupling, was examined both experimentally and theoretically. Dinuclear μ -hydroxo-bridged complexes formed by reaction of trans[ArNi(PR3)2X] with hydroxide are not directly involved in transmetalation, but they rather act as a resting state for the catalyst. The base/boronic acid ratio is the crucial parameter, as it modulates the extent of formation of these dinuclear species and thus tunes the catalytic activity. These findings explain some limitations encountered in practical applications of nickel-catalyzed S-M couplings and suggest how to tailor the experimental conditions in order to overcome these difficulties.

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Références: 

Taming Nickel-Catalyzed Suzuki-Miyaura Coupling: A Mechanistic Focus on Boron-to-Nickel Transmetalation

 

Pierre-Adrien Payard, Luca Alessandro Perego, Ilaria Ciofini, and Laurence Grimaud

 

ACS Catal. 2018, 8, 4812−4823

 

DOI: 10.1021/acscatal.8b00933