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

Abstract

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 1 H NMR, 13 C 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-H 2 O) in high yields. The Suzuki-Miyaura reaction between various aryl/ hetaryl bromides and phenylboronic acids came off in excellent yields in DMF-H 2 O in the presence of K 2 CO 3 as a base with low catalyst loadings (0.1%) at room temperature.

PEPPSI-Type Pd(II)—NHC Complexes on the Base of p-tert-Butylthiacalix[4]arene: Synthesis and Catalytic Activities

“…The so-called PEPPSI (Pyridine-Enhanced Precatalyst: Preparation, Stabilization and Initiation) complexes of palladium (II), introduced into practice by an Organ's group, have recently become popular among catalysts of NHC type [11][12][13]. The latter Pd-PEPPSI complexes show high catalytic activity, with no need for an inert atmosphere and require a low catalyst load [14,15].…”