Abstract
As an earth-abundant first-row transition metal, cobalt catalysts offer a broad range of economical methods for organic transformations via C–H activation. One of the transformations is the addition of C–H to C–X multiple bonds to afford alkylation, alkenation, amidation, and cyclization products using low- or high-valent cobalt catalysts. This hydroarylation is an efficient approach to build new C–C bonds in a 100% atom-economical manner. In this review, the recent developments of Co-catalyzed hydroarylation reactions and their mechanistic studies are summarized.
Highlights
For the last three decades, atom-economical synthetic approaches have played a substantial role in organic synthesis owing to the necessity of green chemistry for the modern universe [1,2,3]
As a member of the first-row transition metals, cobalt complexes are known to be extensively involved in homogeneous catalysis, in particular, C–H activation
The found intermolecular kinetic isotope effect (KIE) of kH/kD = 2.1 and H/D crossover studies strongly suggest that the reaction proceeds through an oxidative addition of a C–H bond to lowvalent cobalt followed by alkyne insertion and reductive elimination
Summary
For the last three decades, atom-economical synthetic approaches have played a substantial role in organic synthesis owing to the necessity of green chemistry for the modern universe [1,2,3]. After 15 years, Murahashi discovered a cobalt-catalyzed chelationassisted ortho C–H carbonylation of azobenzene and imines as the preliminary example of directing group assisted C–H activation reactions (Scheme 1) [29,30]. Nakamura [39], Ackermann [40], and Glorius [41] involved in cobalt-catalyzed C–H functionalization Of these reactions, alkylation, alkenation, amidation, and cyclization of arenes with the relevant coupling partners are an economical and straightforward approach for the synthesis of diverse alkyls, alkenes, amides and cyclic compounds. We wish to review the cobalt-catalyzed hydroarylation of alkynes, alkenes, allenes, enynes, imines, and isocyanates These reactions usually proceed via either an oxidative addition of Ar–H to a low-valent cobalt to form A1 intermediate or a C–H activation with high-valent cobalt to give A2 via deprotonation, followed by migratory insertion and reductive elimination or protonation (Scheme 3). We believe that this review will be helpful to the researchers for their future research on hydroarylation using earth-abundant metal catalysts
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