Steric effects determine the mechanisms of reactions between bis(N-heterocyclic carbene)-nickel(0) complexes and aryl halides

Abstract

Computational investigations of the reactions of [Ni(NHC)2] complexes with aryl halides show that the outcomes are governed by the steric impact of the ligand (NHC = N-heterocyclic carbene). Small ligands permit facile oxidative addition, leading to NiII complexes, while larger NHC ligands prevent coordination of the aryl halide and favour the halide abstraction to form NiI.

Aldehydes and ketones influence reactivity and selectivity in nickel-catalysed Suzuki–Miyaura reactions

“…[9][10][11][12] [Ni(NHC) 2 ] and [Ni(PR 3 ) 4 ] complexes react with aryl halides by oxidative addition or halide abstraction, depending on the ligand and substrate structure. [13][14][15][16][17] [Ni(COD)(dppf)] (1) 18 undergoes oxidative addition to aryl halides, followed by rapid comproportionation to form [NiX(dppf)] ( Fig. 1(a)); 19 we have established the order of reactivity of a series of aryl (pseudo) halides.…”

“…A 'robustness screen' 43,44 was used, in which a model reaction was carried out in the presence of 1 equiv. of each of a series of additives (9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). ** This provides a rapid and quantitative measure of the effect of each additive.…”

Large vs. Small NHC Ligands in Nickel(0) Complexes: The Coordination of Olefins, Ketones and Aldehydes at [Ni(NHC)2]

“…[4] For example, Nelson and Maseras highlighted recently by means of quantum chemical calculations the dominant mechanistic role of steric effects in the reaction of complexes of the type [Ni(NHC) 2 ] with aryl halides (Ph-X, X = Cl, Br, I) and demonstrated that the outcome of this reaction is controlled by the steric impact of the NHC ligand. [5] Small NHC substituents should favor a concerted oxidative addition of the C-X bond to the Ni(0) complex leading to Ni(II) complexes, while larger NHC ligands should prevent coordination of the aryl halide and favor halide radical abstraction to form Ni(I) complexes. [5] However, even though different nickel complexes and an organic NHC-dimethylfumarate coupling product are formed.…”

Four Oxidation States in a Single Photoredox Nickel‐Based Catalytic Cycle: A Computational Study

“…[22] Our group has also recently explored computational SET processes in nickel chemistry,a lthough not under photochemical conditions. [23] We present herein the computational characterization of the full catalytic cycle for ap hotoredox nickel-based process that we consider particularly interesting.T his reaction is the regioselective synthesis of indolines from iodoacetanilides and alkenes recently reported by Tasker and Jamison (Scheme 1). [16] It is ac hemically relevant process,a nd available experimental data hint to ac omplex mechanism with involvement of avariety of nickel oxidation states.…”

“…[16] set collection of computational results is available in the ioChem-BD repository. [24] Then ickel complex 1 (Figure 1) had been experimentally observed, and we used its reaction with 2'-iodoacetanilide as the first step of the computational study.B ased on our previous studies on the reaction of aryl iodides with Ni 0 species, [23] we explored two different pathways:oxidative addition and halide abstraction. Theoxidative addition (in blue in Figure 1) has abarrier of 19.8 kcal mol À1 , 13.7 kcal mol À1 higher than the halide abstraction.…”