Pd‐PEPPSI‐NHC Analogues Bearing Cycloalkane Ring‐Fused Pyridine Ligands: Synthesis, Structure and Catalytic Studies

ABSTRACT The Pd‐PEPPSI‐NHC complexes (PEPPSI = pyridine‐enhanced precatalyst preparation stabilisation initiation, NHC = N ‐heterocyclic carbene) have been widely applied in the Pd‐catalyzed cross‐coupling reactions. Further studies on the structures of Pd‐PEPPSI‐NHC complexes have shown that not only the NHCs, the ancillary ligands surrounding the Pd centre also play important roles in their catalytic reactions. For this purpose, a series of Pd‐PEPPSI‐NHC analogues bearing cycloalkane ring‐fused pyridines (CA‐Py) as the ancillary ligand were readily prepared and characterized by 1 H NMR, 13 C NMR, elemental analysis and x‐ray crystallography. The catalytic activities of the well‐defined Pd–NHC complexes have been evaluated with respect to Suzuki–Miyaura cross‐coupling reactions of aryl boronic acids with aryl chlorides and acyl chlorides, respectively.