Synthesis, characterization and catalytic properties of cis-dibromo{1,1′-di[3,4,5-trimethoxybenzyl]-3,3′-butylenedibenzimidazol-2,2′-diylidene}palladium (II)

An N-heterocyclic carbene palladium-based complex, cis-dibromo{1,1′-di[3,4,5-trimethoxybenzyl]-3,3′-butylenedibenzimidazol-2,2′-diylidene}palladium(II), has been synthesized and characterized by elemental analysis, IR spectroscopy and 1H- and 13C-NMR spectroscopy. The crystal and molecular structure of the title compound was determined by single-crystal X-ray diffraction. The title compound consists of a 1,1′-di[3,4,5-trimethoxybenzyl]-3,3′-butylenedibenzimidazole and two bromo ligands coordinated to a palladium atom in a distorted square-planar cis-system. Two benzoimidazole rings are connected to each other by a C4H8 bridge. The substituted benzimidazole ligand forms a bidentate chelate with palladium, bonding via the carbene carbon atoms. There are two independent molecules A and B in the asymmetric unit. The Pd―Br bonds are 2.4675(14) and 2.4601(13) Å, and the Pd―Ccarbene bonds are 1.985(9) and 1.986(9) Å for molecule A. Each A and B molecule is stabilized with intra- and inter-molecular hydrogen bonds and C―H…π interactions. The palladium–carbene complex was tested as a catalyst in the direct arylation of benzothiazole with arylbromides. The most suitable reaction conditions for the direct arylation of benzothiazole with arylbromides are NMP, K3PO4, Pd–NHC and 130 °C.

Graphical abstractA novel palladium(II) complex bearing N-heterocyclic carbenes has been synthesized by the reaction of bis(benzimidazolium) salt with the Pd(OAc)2 in dimethyl sulfoxide and characterized by elemental analyses, infrared, 1H and 13C NMR spectroscopy and single-crystal X-ray diffraction analysis. The catalytic studies on palladium(II) complex indicate that it is a potent catalyst for even milder reaction conditions such as amination or arylation of various azoles.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights► An N-heterocyclic carbene palladium-based complex has been synthesized. ► The crystal structure of complex was determined by single-crystal X-ray diffraction. ► There are two independent molecules A and B in the asymmetric unit. ► The complex was tested as a catalyst in the direct arylation of benzothiazole. ► The reaction conditions for the direct arylation are NMP, K3PO4, Pd-NHC and 130 °C.