Mechanism of oxidative addition. Reaction of nickel(0) complexes with aromatic halides

Bimetallic Oxidative Addition in Nickel-Catalyzed Alkyl–Aryl Kumada Coupling Reactions

“…17 Based on literature of oxidative addition involving radicals, 5 three possible pathways can be proposed for the coupling: cage-rebound, escape-rebound, and bimetallic oxidative addition (Scheme 1). Kochi proposed a cage-rebound mechanism for the oxidative addition of aryl halide on Ni(0); 8 Finke showed that a Co(III) alkyl Coenzyme B12 model complex underwent a Co to carbon alkyl bond rearrangement via a free alkyl radical, i.e., escape-rebound rather than cage-rebound pathway because the latter was much slower; 25 and finally, oxidative addition on two metals was well known for 17 electron transition metal complexes. 5,26 As reported before, the Ni(II) halide complex 1 is inactive towards alkyl halide, 12 while certain Ni(II) aryl species is active.…”

Mechanistic insight into carbon–fluorine cleavage with a ( Pr3P)2Ni source: Characterization of ( Pr3P)2NiC6F5 as a significant Ni(I) byproduct in the activation of C6F6

“…Although DFT calculations have been done to examine both traditional concerted oxidative addition [8a] and phosphine-assisted pathways of CÀF activation [10], radical pathways involving Ni(I) intermediates are rarely considered computationally, despite precedent in the oxidative addition of other carbon-halide bonds to Ni [11]. Experimentally [12], it has been shown that 2,3,5,6-tetrafluoropyridine reacts with a (Et 3 P) 2 Ni source via a concerted CÀF oxidative addition without phosphine-assistance; however, the more electron-poor pentafluoropyridine reacts via a mechanism that is zeroth order with respect to the mononuclear (PEt 3 ) 2 Ni adduct and with an EPR active species as a likely intermediate.…”

Computational study of the Sonogashira cross-coupling reaction in the gas phase and in dichloromethane solution

“…The catalytically active palladium species is the low-ligated PdL 2 complex (L0monodentate phosphane ligand) or PdL 2 X -anion (X0Cl, Br, I) formed by the dissociation of stable PdL 4 catalyst. The dissociation equilibria of PdL 4 and its analogue NiL 4 have been investigated by Amatore et al and Tsou et al [26,27]. The mechanism of oxidative addition is strongly dependent on the reaction conditions and can change during the course of the reaction, as the halide anion can coordinate with lowligated palladium species and form a new active catalyst [28].…”