Practical One-Pot, Three-Component Synthesis of N-Heterocyclic Carbene (NHC) Ligated Palladacycles Derived fromN,N-Dimethylbenzylamine

Abstract

Further explorations of the catalytic potential of N-heterocyclic carbene (NHC) ligated palladacycles as catalysts for Pd-mediated transformations have been hampered by the lack of general and practical methods for their synthesis. In this work, we describe a novel, practical approach to NHC-ligated palladacycles by a three-component, one-pot reaction of imidazolium salts, PdCl2, and N,N-dimethylbenzylamine in the presence of excess K2CO3 under reflux in reagent-grade acetonitrile in air. 1,3-Diarylimidazolium salts afford the corresponding NHC−Pd(dmba)Cl (dmba = N,N-dimethylbenzylamine-κ2N,C) complexes in >80% yield. The conversion of 1,3-diaryl-4,5-dihydroimidazolium and 1,3-dialkylimidazolium or benzimidazolium salts requires the use of stronger base (Cs2CO3) and/or higher temperature (100 °C). The Pd-bound chloride anion can be exchanged with silver salts or sodium salts. The NHC−palladacycle adducts have been characterized by single-crystal X-ray crystallography.