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Oxidant-free synthesis of benzimidazoles from alcohols and aromatic diamines catalysed by new Ru(II)-PNS(O) pincer complexes

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Abstract

Benzimidazoles are chemically and pharmaceutically important, and an environmentally benign synthetic method based on acceptorless dehydrogenative condensation of primary alcohols and benzene-1,2-diamine is developed in this work. Three Ru(II) hydride complexes [RuHCl(CO)(PNS(O))] (containing two isomers 1a and 1b) and [RuHCl(CO)(PPh3)(SNCNHC)]PF6 (2) based on two new quinoline-based ligands 2-(diphenylphosphanylmethyl)-8-phenylsulfinylquinoline (PNS(O)) and 1-mesityl-3-(8-phenylthioquinolyl-2-methyl)-2-imidazole carbene (SNCNHC) are prepared and fully characterized. These complexes catalyse the condensation of benzyl alcohol and benzene-1,2-diamine to 2-phenylbenzimidazole with the liberation of H2, and the catalytic activity follows the order: 1a1b > 2. When 0.2 mol% of 1a and 2 mol% of NaBPh4 were used, various 2-functionalized benzimidazoles were obtained in good yields (70–85%) and high turnover numbers (TONs ∼ 425). This homogeneous system does not need oxidants or stoichiometric strong bases (KOH or KOtBu, etc.) that are normally used in the reported homogeneous systems, and thus is a greener process.

Graphical abstract: Oxidant-free synthesis of benzimidazoles from alcohols and aromatic diamines catalysed by new Ru(ii)-PNS(O) pincer complexes

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Publication details

The article was received on 17 Jul 2017, accepted on 28 Sep 2017 and first published on 29 Sep 2017


Article type: Paper
DOI: 10.1039/C7DT02584J
Citation: Dalton Trans., 2017, Advance Article
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    Oxidant-free synthesis of benzimidazoles from alcohols and aromatic diamines catalysed by new Ru(II)-PNS(O) pincer complexes

    Q. Luo, Z. Dai, H. Cong, R. Li, T. Peng and J. Zhang, Dalton Trans., 2017, Advance Article , DOI: 10.1039/C7DT02584J

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