Palladium hetero-di(N-heterocyclic carbene) complexes and their catalytic activities in direct C-H arylation of heteroarenes

A library of neutral and cationic palladium complexes of cis-chelating hetero-dicarbene ligands have been prepared. These ligands contain two different NHC donors allowing for a wider degree of variation, and the impact of the distinct NHC units has been compared using various spectroscopic means. In addition, the catalytic activities of these complexes in the direct C-H arylation of thiophenes with aryl halides were studied leading to the finding that the neutral dibromido complexes of the type [PdBr2(diNHC)] generally outperformed their cationic [Pd (NCMe)(2)(diNHC)](OTf)(2) counterparts. More importantly, complexes containing more distinct NHC units give rise to superior catalysts due to an amplified stereoelectronic asymmetry within the complex. A preliminary photophysical study of some selected thiophene reaction products has been conducted as well. The ability to individually change each NHC donor in such dicarbene ligands allows for a better fine-tuning of complex properties in search for superior catalysts.

Automated summary

A library of neutral and cationic palladium complexes of cis-chelating hetero-dicarbene ligands have been prepared and their catalytic activities have been studied. It was found that complexes containing more distinct NHC units exhibited superior catalytic performance.