Direct synthesis of benzimidazoles by Pd(II) N∧N∧S-pincer type complexes via acceptorless dehydrogenative coupling of alcohols with diamines

A sustainable synthetic method for the construction of substituted benzimidazoles via acceptorless de-hydrogenative coupling of primary alcohols by palladium catalysts is reported. Three new non-classical symmetric Pd(II) N boolean AND N boolean AND S pincer complexes (1-3) were synthesized and characterized by spectral (FT-IR, UV-vis, NMR and ESI-MS) and analytical techniques. Moreover, the distorted square planar geometry of the synthesized complexes 1 and 2 was confirmed by single-crystal X-ray diffraction study. A wide range of benzimidazole derivatives (32 examples) up to 94% isolated yield has been derived via acceptorless dehydrogenative coupling of primary alcohols with derivatives of o-phenylenediamines. The present pro-tocol operates smoothly with only 1 mol% catalyst loading. Furthermore, the mechanistic investigation with the aid of control experiments revealed that the reaction proceeded through in situ generation of aldehyde intermediate and generates hydrogen and water as the only byproducts. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

A sustainable synthetic method for substituted benzimidazoles was reported via acceptorless de-hydrogenative coupling of primary alcohols using palladium catalysts. New non-classical Pd(II) N boolean AND N boolean AND S pincer complexes (1-3) were synthesized and characterized. The complexes exhibited distorted square planar geometry, confirmed by single-crystal X-ray diffraction study. The reaction showed high efficiency with 94% isolated yield and only 1% catalyst loading, generating aldehyde intermediate, hydrogen, and water as the only byproducts.