Novel meta-benzothiazole and benzimidazole functionalised POCOP-Ni(ii) pincer complexes as efficient catalysts in the production of diarylketones

Abstract

The synthesis of four novel non-symmetric Ni(II)-POCOP pincer complexes meta-functionalized with either benzothiazole or benzimidazole at the central aryl ring is described. All complexes were fully characterised in solution by various analytical techniques and the molecular structures in the solid state of complexes 1b, 2a and 2b were unequivocally determined by single crystal X-ray diffraction analysis. In addition, the Ni(II)-POCOP pincer complexes were efficiently used as catalysts in the synthesis of diarylketones by cross-coupling reactions of functionalized benzaldehydes and boronic acid derivatives under relatively mild conditions. An important aspect of this transformation is the dependence on the steric properties of the donor groups (OPR₂) of the pincer ligands, the more active compounds having the phosphinitos bearing isopropyl groups (1a and 2a) than those containing tert-butyl substituents (1b and 2b).