Jump to main content
Jump to site search


Trinuclear complexes of palladium(II) with chalcogenated N-heterocyclic carbenes: catalysis of selective nitrile-primary amide interconversion and Sonogashira coupling

Abstract

3-Methyl-1-(2-(phenylthio/seleno)ethyl)-1H-benzo[d]imidazol-3-ium iodide (L1/L2), precursor of sulfated/selenated N-heterocyclic carbine, was synthesized by reaction of benzimidazole with 1,2-dichloroethane followed by treatment with PhS/SeNa and MeI. The reaction of L1/L2 with Ag2O followed by treatment with [Pd(CH3CN)2Cl2] (metal to ligand ratio 3:2), i.e. transmetallation, resulted in trinuclear palladium(II) complexes, [Pd3(L1/L2-HI)2(CH3CN)Cl6] (1-2). The complexes were characterized with 1H, 13C{1H} and 77Se{1H} NMR (2 only), elemental analyses, HR-MS and single-crystal X-ray diffraction. The geometry of three Pd atoms in each complex is nearly square planar. The Pd-S/Se, Pd-C, Pd-N and Pd-Cl bond distances (Å) in 1/2 are 2.3178(19)/2.4289(8), 1.968(7)/1.958(7), 2.073(8)/2.082(7) and 2.2784(19)-2.298(2)/2.292(2)-2.298(2) respectively. In both the complexes, all Cl are trans to each other. For central Pd atom two benzimidazole rings are also trans to each other. The C-H∙∙∙∙Cl non-covalent interactions result in three-dimensional network. The moisture and air insensitive trinuclear Pd(II) complexes, 1 and 2 are thermally stable and efficient as a catalyst for nitrile-amide interconversion and amine free Sonogashira C-C coupling (in the presence of CuI). The optimum temperature is 80 °C for the interconversion and 110 °C for the coupling. The catalytic protocols are applicable to both aliphatic and aromatic amides/nitriles. The optimum catalyst loading is 1 mol% for the C-C coupling and 0.5 to 1 mol% for the interconversion. The K2CO3 as a base gives best result for Sonogashira C-C coupling. In the conversion of nitrile to amide, formation acid was not detected. The 1/2 after using once can carry out conversion of ten fresh lots of nitrile to amide with same almost efficiency. The real catalytic species for the interconversion and coupling appear to be based on Pd(II) and Pd(0) respectively

Back to tab navigation

Supplementary files

Publication details

The article was received on 17 Jul 2017, accepted on 07 Sep 2017 and first published on 08 Sep 2017


Article type: Paper
DOI: 10.1039/C7DT02592K
Citation: Dalton Trans., 2017, Accepted Manuscript
  •   Request permissions

    Trinuclear complexes of palladium(II) with chalcogenated N-heterocyclic carbenes: catalysis of selective nitrile-primary amide interconversion and Sonogashira coupling

    A. K. Singh, P. Dubey and S. Gupta, Dalton Trans., 2017, Accepted Manuscript , DOI: 10.1039/C7DT02592K

Search articles by author

Spotlight

Advertisements