Unravelling the Mechanism of Nickel Mediated Cross‐Electrophile‐ Electrophile Coupling Between Katritzky Salts and Acid Chlorides

Abstract

Dedicated to Professor Oliver Reiser on the occasion of his 60th birthdayModern nickel-mediated cross-electrophile coupling reactions devoid of organometallic nucleophiles have garnered a great deal of interest due to their ability to enhance functional group compatibility. Despite the recent advances in the field, various mechanistic pathways, such as radical chain and sequential oxidative addition, in addition to finding the active nickel species and reductant, render the reaction complex. Although the reduction of Ni(II) complexes by heterogeneous Mn could produce either Ni(I) or Ni(0) species, the latter is more generally proposed as an active species. Likewise, Ni(I) mediated reduction of pyridinium salts is commonly invoked to generate the transient alkyl radicals. In stark contrast, we present a comprehensive mechanistic examination and experimental evidence for the intermediacy of Ni(I) species, a synergistic reduction of pyridinium salts by Ni(I) and Mn. Using a combination of kinetic analysis, control experiments, and spectroscopic methods, the rate-limiting reductive alkylation and resting state Ni(II) species have been identified.

Application of Solid Me3SiZnI for the Synthesis of Aryl and Alkyl Trimethylsilanes

“…In anticipation of a radical intermediate, [21] TEMPO was introduced to the optimal reaction conditions and the suppression of the silylation was observed (SI‐43). Using a radical clock substrate (SI‐44), we discovered that the cyclized product is produced at a yield of 52%, which confirms the presence of transient alkyl radical species in the medium.…”

“…In figure 1, we have proposed a plausible mechanism, [21,24] When Ni(II)dtbpy was exposed to Me 3 SiZnI ⋅ TMEDA, Ni(0) species is produced, which may be in equilibrium with a weak Ni(0)−SiMe 3 ‐ate complex [19b,24–25] . Single electron transfer (SET) to alkyl bromide generates intermediate II , where the produced alkyl radical is anticipated to be cage‐bound by solvent.…”

“…[22] Additionally, benzyltrimethylsilane 6 d was treated with (E)À N,1-diphenylmethanimine 10 (Aza-Peterson olefination) in the presence of n-BuLi and KO t Bu in THF to produce (E)-1,2-diphenylethene 11 with an isolated yield of 80% (Scheme 2b). [23] In figure 1, we have proposed a plausible mechanism, [21,24] When Ni(II)dtbpy was exposed to Me 3 SiZnI • TMEDA, Ni(0) species is produced, which may be in equilibrium with a weak Ni(0) À SiMe 3 -ate complex. [19b,24-25] In conclusion, we have demonstrated the efficacy of our solid trimethylsilyl zinc reagent in the synthesis of aryl and alkyl trimethylsilanes.…”

Anti‐Selective Carbosilylation: Nickel‐Catalyzed Multicomponent Reaction of Solid Me3SiZnI

“…Based on our previous observations, [19] we anticipated that α-bromo carbonyls would generate an alkyl radical. Consequently, TEMPO was employed under optimal conditions, resulting in a trace amount of the cross-coupled product 4 a (SI-S58).…”