Investigating Oxidative Addition Mechanisms of Allylic Electrophiles with Low-Valent Ni/Co Catalysts Using Electroanalytical and Data Science Techniques

Abstract

The catalysis by a π-allyl-Co/Ni complex has drawn significant attention recently due to its distinct reactivity in reductive Co/Ni-catalyzed allylation reactions. Despite significant success in reaction development, the critical oxidative addition mechanism to form the π-allyl-Co/Ni complex remains unclear. Herein, we present a study to investigate this process with four catalysis-relevant complexes: Co(MeBPy)Br2, Co(MePhen)Br2, Ni(MeBPy)Br2, and Ni(MePhen)Br2. Enabled by an electroanalytical platform, Co(I)/Ni(I) species were found responsible for the oxidative addition of allyl acetate. Kinetic features of different substrates were characterized through linear free-energy relationship (Hammett-type) studies, statistical modeling, and a DFT computational study. In this process, a coordination-ionization-type transition state was proposed, sharing a similar feature with Pd(0)-mediated oxidative addition in Tsuji–Trost reactions. Computational and ligand structural analysis studies support this mechanism, which should provide key information for next-generation catalyst development.

Interrogating the Mechanistic Features of Ni(I)-Mediated Aryl Iodide Oxidative Addition Using Electroanalytical and Statistical Modeling Techniques

“…Our group − and others have reported an electroanalytical approach to study oxidative addition processes involving low-valent first-row transition metals into alkyl electrophiles. The rate of oxidative addition is measured using cyclic voltammetry through peak-ratio analysis.…”

“…(See the Supporting Information for a more detailed discussion.) In prior studies, we have applied this method to study the oxidative addition processes of activated sp 3 electrophiles such as benzyl halides − and allyl electrophiles . However, this method is yet to be applied to the reaction of aryl electrophiles.…”

“…The rate constants for the chemical step in the EC mechanism were determined using peak-ratio analysis. − The ratios of forward and return peak currents were measured using CV for Ni complexes and phenyl iodide at different scan rates. The rate constants were subsequently obtained by correlating the peak ratios and scan rates.…”

“…15,24 This is likely due to speciation processes by Ni(II) and disproportionation processes by Ni(I), 15 which prevent further application of this technique for quantitative analysis. Inspired by previous reports, 38,53 we hypothesized that placing methyl groups adjacent to the nitrogen atoms of the ligands could minimize speciation issues and stabilize the nickel center from undesired disproportionation reactions through steric shielding of the metal center. Indeed, we found that Me BPy (6,6′-dimethyl-2,2′-bipyridine) and Me Phen (neocuproine) were effective ligands and provided interpretable CVs for the nickel complexes.…”

Light-Induced Access to Carbazole-1,3-dicarbonitrile: A Thermally Activated Delayed Fluorescent (TADF) Photocatalyst for Cobalt-Mediated Allylations

“…In recent years, several authors have suggested that the reaction follows a Co(II)−Co(I)−Co(III)−Co(II) cycle. 27,29,39,42 39 the reactive organometallic species that can react with aldehydes by a Zimmerman−Traxler transition state. 41 2 [E(2 •+ /2) = +1.31 V vs SCE (see Table 1)] was restored to the initial state by HE [E(HE •+ /HE) = +1.0 V vs SCE].…”