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Issue 40, 2019
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Palladium(ii) ligated with a selenated (Se, CNHC, N)-type pincer ligand: an efficient catalyst for Mizoroki–Heck and Suzuki–Miyaura coupling in water

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Abstract

A new 1-[N-benzylacetamido]-3-[1-(2-phenylselenylethyl)]benzimidazolium chloride (L), the precursor of a novel (Se, CNHC, N)-type pincer ligand (L) was synthesised in high yield through a sequence of consecutive reactions of 1H-benzimidazole with ethylene dichloride, sodium selenophenolate, and N-benzyl-2-chloroacetamide. The palladium-promoted reaction of L with PdCl2 resulted in a moisture- and air-insensitive complex [Pd(L–H2Cl)Cl] (1), which demonstrated outstanding catalytic potential for Mizoroki–Heck coupling of aromatic bromides and chlorides (with yields up to 94% and 70%, respectively) at very low catalyst loading (0.2 mol%) and under mild reaction conditions in water. The complex (1) was also investigated for Suzuki–Miyaura coupling and found to be selectively efficient (yields up to 94%) for Suzuki–Miyaura coupling of aromatic bromides at 0.01 mol% of 1 in water. All coupling reactions were carried out in the green and economical solvent, water, which is highly desirable for bulk synthesis of complex molecules in industry. During the catalytic process, complex 1 converted into PdSe nanoparticles (NPs, size range 5–6 nm) in situ. The morphology and composition of these NPs were analysed through high-resolution transmission electron microscopy and transmission electron microscopy-energy dispersive X-ray spectroscopy, respectively. The core-level, X-ray photoelectron spectroscopy analysis confirmed the presence of stable Pd0 and Pd2+ oxidation states in these PdSe NPs. Based on further experimental investigations, these nanoparticles were found to work as a stock of true catalytic species. The hot filtration test, as well as the two-phase test, confirmed the largely homogeneous nature of the catalytic process, which probably proceeds by leaching of solution-phase Pd species from these NPs.

Graphical abstract: Palladium(ii) ligated with a selenated (Se, CNHC, N−)-type pincer ligand: an efficient catalyst for Mizoroki–Heck and Suzuki–Miyaura coupling in water

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Publication details

The article was received on 29 Jul 2019, accepted on 07 Sep 2019 and first published on 09 Sep 2019


Article type: Communication
DOI: 10.1039/C9OB01674K
Org. Biomol. Chem., 2019,17, 8969-8976

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    Palladium(II) ligated with a selenated (Se, CNHC, N)-type pincer ligand: an efficient catalyst for Mizoroki–Heck and Suzuki–Miyaura coupling in water

    K. N. Sharma, N. Satrawala, A. K. Srivastava, M. Ali and R. K. Joshi, Org. Biomol. Chem., 2019, 17, 8969
    DOI: 10.1039/C9OB01674K

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