Bimetallic Pd complexes with NHC/Py/PCy donor set ligands: applications in α-arylation, Suzuki-Miyaura and Sonogashira coupling reactions

Bimetallic complexes bearing NHC donor ligands are gaining immense popularity as catalysts in organometallic chemistry. However, such complexes with a mixed NHC/PR 3 donor set ligands are still rare. We present here a series of bimetallic Pd II complexes featuring mixed NHC/Py/PCy 3 donor set ligands applied in α-arylation of amide, Suzuki-Miyaura coupling and Sonogashira coupling reactions. All complexes have been characterized using standard characterization techniques and one of the complexes has been structurally characterized by X-ray crystallographic analysis. Catalytic outcomes clearly indicate the superior activity of Pd II complex bearing mixed NHC/PCy 3 donor set ligands compared to the PEPPSI-type complexes in both α-arylation of amide and Sonogashira coupling reactions, though almost similar activities were observed for all the complexes in Suzuki-Miyaura coupling reactions. This observation might be due to the involvement of Pd-NPs as an active catalyst in Suzuki-Miyaura coupling reactions, whereas the Hg-poison test suggested the homogeneous nature of the other two types of reactions. Two pyridine rings in a mixed NHC/4-OMe(Py) donor complex are oriented almost in a parallel face-to-face fashion with a centroid to centroid separation of 3.758 Å, indicating π···π interactions between two methoxypyridine rings. This interaction leads to a very short Pd···Pd distance of 5.754 Å in the aforementioned complex. Bimetallic Pd II complexes bearing mixed NHC/Py/PCy 3 donor set ligands are presented. A complex with a mixed NHC/PCy 3 donor set ligands shows superior activity compared to the PEPPSI type complexes in α-arylation and Sonogashira coupling reactions.