Palladium hetero-dicarbene complexes have been prepared and tested for their catalytic activities in the direct C-H arylation of thiophenes with aryl halides. Complexes containing more distinct NHC units give rise to superior catalysts due to an amplified “stereoelectronic asymmetry.” 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.
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.