The Regioselective Switch for Amino-NHC Mediated C–H Activation of Benzimidazole via Ni–Al Synergistic Catalysis

Abstract

We have disclosed a new mode of a chemically regioselective switch for C-H bond functionalization of benzimidazole derivatives via a cooperative effect invoked by Ni-Al bimetallic catalysis to create a steric requirement for obtaining the linear product of styrene insertion. Yet, excluding the AlMe(3) cocatalyst switches the reaction toward branch selectivity.

Mechanistic Study of a Switch in the Regioselectivity of Hydroheteroarylation of Styrene Catalyzed by Bimetallic Ni–Al through CH Activation

“…Furthermore, the identity of 3 was confirmed by a single‐crystal X‐ray study, which revealed that AlMe 3 was datively coordinated to the benzimidazole nitrogen (Figure 2). 7a, 8 Thus, we postulated that coordination of the Lewis acid to benzimidazole would increase the acidity of the C2H bond, resulting in the observed higher activity. It is imperative to mention the recent advances in the use of Lewis acid additives to enhance reaction rates; for example, the groups of Hartwig, Nolan, and Knochel have employed the Lewis acids AlCl 3 and BEt 3 for reductive elimination reactions mediated by palladium 3…”

“…Our group has previously reported the direct amino‐NHC nickel‐catalyzed hydroheteroarylation of styrene with benzimidazole by CH bond activation, as summarized in Table 1 7a. High selectivity in favor of the branched product with good yield was observed with various styrene substrates.…”

Iridium‐Catalyzed Regio‐ and Enantioselective Hydroarylation of Alkenyl Ethers by Olefin Isomerization

“…[1] Thepioneering studies on the transition-metal-catalyzed alkene hydroarylation by Murai and co-workers have described high linear selectivity in the reaction with terminal alkenes. [1b] Recently,b ranchselective hydroarylation [2] has also emerged for vinylarenes, [3] vinyl ethers, [4] and simple alkenes. [5] Although the regiocontrolled hydroarylation reactions of terminal alkenes leading to chiral molecules have been developed, the use of ac hiral catalyst for this asymmetric transformation remains to be studied.…”

Catalytic Intermolecular Functionalization of Benzimidazoles

“…Rhodium(I)-catalyzed linear C-2 alkylation was reported first by Bergman and Ellman [20]. In 2012, Shih et al reported alkylations with full Catalytic Intermolecular Functionalization of Benzimidazoles DOI: http://dx.doi.org/10.5772/intechopen.87068 control of linear versus branched selectivity using AlMe 3 as a chemical switch (Figure 10) [21]. In the presence of 10 mol% of Ni(cod) 2 (cod = cyclooctadiene) and the bidentate N-heterocyclic carbene (NHC) ligand 24 in toluene, the reaction between N-methylbenzimidazole and substituted styrenes 25 afforded exclusively branched alkylation products 26 in 50-98% yields.…”

“…The branched product is electronically favored, but the linear product arises in the presence of AlMe 3 because the benzimidazole nitrogen at position 3 will generate a Lewis acid/base adduct causing a steric switch in the preferred binding orientation of the styrene during the catalytic cycle. Thus, the linear product is formed predominantly [21].…”