Pd-PEPPSI type complexes bearing unsymmetrical NHC ligand with phenyl-substituted backbone: Highly efficient catalysts for Heck-Mizoroki and Suzuki-Miyaura cross-coupling reactions

A series of air-stable NHC-Pd-PEPPSI-type complexes bearing unsymmetrical NHC ligand, with a phenyl group in its backbone, were synthesized in excellent yields (82%-94%). Air and moisture-stable complexes were characterized by using H-1 NMR, C-13 NMR, FT-IR spectroscopy, and HRMS techniques. Single-crystal X-ray diffraction method was used to determine the crystal and molecular structure of the complexes. The molecular structure adopts slightly distorted square planar geometry around the metal centre and was refined as an inversion twin. The complexes were screened for their catalytic activities in Heck-Mizoroki and Suzuki-Miyaura cross-coupling reactions. Heck-Mizoroki reaction between the various aryl/hetaryl bromides and styrenes occurred in good to excellent yields in DMF in the presence of NaOAc as a base with low catalyst loadings (0.5%). The reactions also occur in aqueous media (DMF-H2O) in high yields. The Suzuki-Miyaura reaction between various aryl/hetaryl bromides and phenylboronic acids came off in excellent yields in DMF-H2O in the presence of K2CO3 as a base with low catalyst loadings (0.1%) at room temperature.

Automated summary

A series of air-stable NHC-Pd-PEPPSI-type complexes with unsymmetrical NHC ligand and a phenyl group in its backbone were successfully synthesized with high yields (82%-94%). The complexes were characterized by various spectroscopic techniques, including H-1 NMR, C-13 NMR, FT-IR spectroscopy, and HRMS. The crystal structure of the complexes was determined using single-crystal X-ray diffraction, showing a slightly distorted square planar geometry around the metal centre. The complexes exhibited excellent catalytic activities in Heck-Mizoroki and Suzuki-Miyaura cross-coupling reactions under low catalyst loadings.