Pd^II Triazolylidene Complexes: Ancillary Ligand Dependent Catalytic Applications in Sonogashira Coupling and α‐Arylation Reactions under Copper‐Free Conditions

Abstract

Complexes ofN‐heterocyclic carbenes have become an irrefutable class of molecules for the researchers in the field of organocatalysis. They rank as one of the potent tools in organic chemistry, which have a wide range of uses in various commercially important processes. Palladium(II) mesoionic carbene (MIC) complexes embedded with PPh3 as an ancillary ligand appeared to be efficient catalysts for the aforementioned purpose. Two new triazolylidene‐based palladium(II) complexes bearing either Py or PPh3 as an ancillary ligand were synthesized, with chirality present at one of the nitrogen atoms of the triazolylidene moiety. The MIC unit in these complexes possesses a mesityl group at the C‐wingtip and 1‐(1‐naphthyl)ethyl substitution at the N‐wingtip. NMR spectroscopy and ESI mass spectrometry were utilized to analyze these complexes. For the determination of the structure of the palladium(II) complex possessing mixed MIC and PPh3 donor ligands, single crystal X‐ray diffraction was utilized. The new complexes were employed in α‐arylation reaction and Sonogashira coupling reactions under copper‐free conditions. While studying their catalytic activity, it was brought to the conclusion that the PdII MIC complex having PPh3 as an ancillary ligand surpassed the complex with Py as an ancillary ligand.The catalytic results of these complexes are also correlated with cyclic voltammetric (CV) data.