Some mechanistic aspects of a nickel-catalyzed electrochemical cross-coupling between aryl halides and substituted chloropyridazines

Enantioselective Ni-Catalyzed Electrochemical Synthesis of Biaryl Atropisomers

“…Furthermore, the addition of 1p to 5 resulted in the loss of the oxidation peak, indicative of a Ni(0)/Ni(I) redox couple, indicating that oxidative addition of 1p to Ni(0) occurred readily (Figure 1). 25 Based on literature precedent 25,26 and our results, a plausible mechanism is presented for this Ni-catalyzed electrochemical reductive coupling process (Scheme 4). Initially, the Ni(II) catalyst is reduced to Ni(0) upon cathodic reduction.…”

“…In addition, complex 5 showed three reductive peaks (−1.52 V, −1.70 V, and −2.02 V vs Ag/Ag + ), corresponding to the successive formation of nickel(I), nickel(0), and [nickel(0)pyrox] •− species (Figure 1). 25 In contrast, the reduction potentials of substrate 1p are around −2.30 V and −2.64 V vs Ag/Ag + (see Figure S1 in the Supporting Information for details), which indicates that the Ni(II) catalyst is likely to be preferentially reduced in favor of aryl halides in this electrochemical reductive coupling reaction. Furthermore, the addition of 1p to 5 resulted in the loss of the oxidation peak, indicative of a Ni(0)/Ni(I) redox couple, indicating that oxidative addition of 1p to Ni(0) occurred readily (Figure 1).…”

An Electrochemical Synthesis of Functionalized Arylpyrimidines from 4-Amino-6-Chloropyrimidines and Aryl Halides

“…At this stage, an oxidative addition of Ni(0) into the C-X bond of either chloropyrimidine or aryl halide should be envisaged. A recent electroanalytical work dedicated to the mechanistical investigation of cross-coupling reactions involving chloropyridazine [ 24 ] has reported that the oxidative addition proceeds faster with the chloropyridazine than with the aryl halide. This should also be likely the case with pyrimidines derivatives, which should give rise to the formation of HetArNi II Cl species.…”

“…We reported recently the preparation of aryl- and heteroarylpyridazines by an electrochemical cross-coupling procedure employing an iron sacrificial anode [ 22 ] and a nickel catalyst [ 23 , 24 ]. In the continuation of this preceding work, we would like to report herein the extension of our electrochemical procedure to the preparation in moderate to high yields of a range of novel 4-amino-6-chloropyrimidines 3 .…”

Recent Advances in Metal-Catalyzed, Electrochemical Coupling Reactions of sp2 Halides/Boronic Acids and sp3 Centers

“…Recent developments in the mechanistic understanding of this reaction have translated to many practical advances. 17,18,20,21 The mechanism of nickel sp 2 -sp 3 couplings has been extensively studied and has been proposed to go through the radical chain mechanism shown in Scheme 1. 17 The first step in the catalytic cycle is the generation of the active Ni 0 catalyst (Int2) from the Ni II halide precatalyst (Int1) through a two-electron reduction.…”