Synthesis, structures and catalysis of Pd(II)–N-heterocyclic carbene complexes of pyridine/pyrimidine wingtip substituted ligand

Starting from precursors 2-(pyridine-2-yl)imidazo[1,5-a]pyridin-4-ylium;hexafluorophosphate (1) and 2-(pyrimidine-2-yl)imidazo[1,5-a]pyridin-4-ylium;hexafluorophosphate (2), novel Pd–NHC complexes 2-pyridyl imidazo-3-ylidene palladium(II)chloridehexafluorophosphate, [Pd(1-H)(CH3CN)Cl][PF6] (1a) and 2-pyrimidyl imidazo-3-ylidene palladium(II)chloridehexafluorophosphate, [Pd(2-H)2Cl][PF6] (2a) have been synthesized and structurally characterized. The geometry of two distorted square planar complexes are different in solid state; in case of 1a, coordination geometry is completed by Ccarbene, Npyridine, chloride and one solvent acetonitrile molecule where as in 2a geometry is completed by Ccarbene, Npyrimidine and chloride. It is expected due to steric crowding of α-CH3 in pyridine wingtip in 1 rule out to approach the second ligand. The complex 1a and 2a are excellent catalysts for Suzuki–Miyaura C–C coupling reactions. In addition to this, theoretical studies have been performed to develop an insight into the experimental results.