Abstract
An efficient method for ambient-temperature synthesis of a variety of 2-substituted and 1,2-disubstituted benzimidazoles from aldehyde and phenylenediamine substrates has been developed by utilizing Co(III)/Co(II)-mediated redox catalysis. The combination of only 1 mol% of Co(acac)2 and stoichiometric amount of hydrogen peroxide provides a fast, green, and mild access to a diversity of benzimidazoles under solvent-free conditions.
Highlights
We report the development of a Co(acac)2-based redox catalytic system for fast, green, and mild synthesis of a of a Co(acac) catalytic system for fast, green, and mild synthesis of a variety
MoO2(acac)2 was selected as a multivalent transition metal catIn our initial attempt, MoO22 was selected as a multivalent transition metal alyst to replace phosphomolybdic acid (PMA) Keggin cluster in our previously reported redox catalytic system
The experimental result the possibility to replace large polyoxometalate (POM) cluster catalyst with a small moproved the possibility to replace large polyoxometalate (POM) cluster catalyst with a small lecular multivalent transition metal complex to catalyze the oxidative dehydrogenation of molecular multivalent transition metal complex to catalyze the oxidative dehydrogenation benzimidazoline
Summary
The catalytic approaches based on oxidants including oxone [22], 1,4-benzoquinone [23], iodobenzene diacetate [24], I2 [25], MnO2 [26], I2 /UHP [27], and (NH4 ) Ce(NO3 )6 /H2 O2 [28] could proceed at faster reaction rate (several minutes to a few hours) under milder conditions (RT to 50 ◦ C), showing that oxidative dehydrogenation is the rate-determining step. Functionalized dendrimers [29], mesoporous materials [30], and nanoparticles [31,32,33] have emerged as new effective catalysts for benzimidazole synthesis. We report the development of a Co(acac)2-based redox catalytic system for fast, green, and mild synthesis of a of a Co(acac) catalytic system for fast, green, and mild synthesis of a variety.
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