The Effect of Added Ligands on the Reactions of [Ni(COD)(dppf)] with Alkyl Halides: Halide Abstraction May Be Reversible

Greaves, Megan; Ronson, Thomas O.; Maseras, Feliu; Nelson, David J.

doi:10.1021/acs.organomet.1c00280

Cited by 16 publications

(12 citation statements)

References 63 publications

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“…Calculations were carried out with Gaussian 16 (ref. 31 ) using M06/6-311+G(d,p)/SMD (benzene)//B3LYP-D3/6-31G(d)+LANL2TZ(f) as described previously for similar systems; 32 full details can be found in the ESI. † All energies are quoted as free energies in benzene solution relative to [Ni(dppf)(COD)] ( 2 ).…”

Section: Resultsmentioning

confidence: 99%

“…2 ). Similarly to the corresponding reaction of bromo-benzene with 2 , 32 they proceed via ligand exchange to form intermediate [Ni(η 2 -ArCl)(dppf)] complexes ( A ); this is followed by an oxidative addition transition state ( A-B-TS ) that leads to a square planar [Ni(Ar)(Cl)(dppf)] complex ( B ). In most cases, this nickel( ii ) complex then undergoes comproportionation to form a nickel( i ) complex, as has been established previously.…”

Section: Resultsmentioning

confidence: 99%

“…10 kcal mol −1 or 20 kcal mol −1 above 2 in free energy terms. We have previously shown that halide abstraction reactions between aryl halides and 2 are not competitive with the alternative oxidative addition pathway, 32 and instead are likely to occur when a three-coordinate intermediate 15,34 or a sterically-encumbered nickel(0) complex is the reactive species. 35 …”

Section: Resultsmentioning

confidence: 99%

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Inhibition of (dppf)nickel-catalysed Suzuki–Miyaura cross-coupling reactions by α-halo-N-heterocycles

et al. 2021

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Inhibition of (dppf)nickel-catalysed Suzuki–Miyaura cross-coupling reactions by α-halo-N-heterocycles

et al. 2021

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“…Small ligands permit oxidative addition to give Ni(II) complexes, while larger NHC ligands favor halide abstraction to form Ni(I) complexes. Alkyl halides react with Ni(0) complexes through initial halogen atom abstraction to form alkyl radicals R· and (L) n Ni(I)X species. ,− The reaction rates vary in the order tert -butyl > sec -butyl > n -butyl and RI > RBr > RCl . The radical pairs formed after halogen atom abstraction can then undergo combination within the solvent cage to give (L) n Ni(II)RX complexes, or the radical could escape the cage and participate in further reactions.…”

Section: Main Partmentioning

confidence: 99%

“…The calculated energy barriers for halide abstraction with Ni(0) complexes from alkyl halides are usually low and vary from 0.21 kcal/mol (bromide abstraction from CyBr with LNi(0) complex, L = 4,4′-dimethyl- 2,2′-bipyridine, the gas phase) to ∼22 kcal/mol (chloride abstraction from (2-chloroethyl)benzene with partially predissociated three-coordinate [Ni(dppf) 2 ] in benzene) . Electron-rich ligands accelerate the reaction …”

Section: Main Partmentioning

confidence: 99%

Nickel and Palladium Catalysis: Stronger Demand than Ever

2022

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Key similarities and differences of Pd and Ni in catalytic systems are discussed. Overall, Ni and Pd catalyze a vast number of similar C−C and C−heteroatom bond-forming reactions. However, the smaller atomic radius and lower electronegativity of Ni, as well as the more negative redox potentials of low-valent Ni species, often provide higher reactivity of Ni systems in oxidative addition or insertion reactions and higher persistence of alkyl-Ni intermediates against β-hydrogen elimination, thus enabling activation of more reluctant electrophiles, including alkyl electrophiles. Another key point relates to the higher stability of the open-shell electronic configurations of Ni(I) and Ni(III) compared with Pd(I) and Pd(III). Nickel systems very often involve a number of interconvertible Ni (n+) active species of variable oxidation states (Ni(0), Ni(I), Ni(II), and Ni(III)). In contrast, catalytic reactions involving Pd(I) or Pd(III) active species are still relatively less developed and may require facilitation by special ligands or merging with photo-or electrocatalysis. However, the relatively high redox potentials of Pd (n+) species ensure their facile reduction to Pd (0) species under the assistance of numerous reagents or solvents, providing relatively high concentrations of molecular Pd 1 (0) complexes that can reversibly aggregate into active Pd n clusters and nanoparticles to form a cocktail of interconvertible Pd n (0) active species of various nuclearities (i.e., various values of "n"). Nickel systems involving Ni(0) complexes often require special strong reductants; they are more sensitive to deactivation by air and other oxidizers and, as consequence, often operate at higher catalyst loadings than palladium systems in the same reactions. The ease of activation and relatively high stability of low-valent active Pd species provide high robustness and versatility for palladium catalysis, whereas a variety of Ni oxidation states enables more diverse and uncommon reactivity, albeit requiring higher efforts in the activation and stabilization of nickel catalytic systems. As a point for discussion, we may note that Pd catalytic systems may easily form a "cocktail of particles" of different nuclearities but similar oxidation states (Pd 1 , Pd n , Pd NPs), whereas nickel may behave as a "cocktail of species" in different oxidation states but is less variable in stable nuclearities. Undoubtedly, there is stronger demand than ever not only to develop improved efficient catalysts but also to understand the mechanisms of Pd and Ni catalytic systems.

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