Direct coupling of oxazolines and N-heterocyclic carbenes:: A modular approach to a new class of C-N donor ligands for homogeneous catalysis

Reaction of 1-mesityl imidazole With 2-bromo-4,4-dimethyloxazoline gave the 2(4,4-dimethyl)oxazolinyl imidazolium salt 1, which was-converted to the silver N-heterocyclic carbene complex [Ag-I(carbene)Br] by stirring 1 with Ag2O in dichloromethane at room temperature. The crystal structure. analysis confirmed the monomeric nature of complex 2, the coordination around the metal being quasi-linear with a C(1)-Ag-Br bond angle of 169.4(1)degrees and a Ag-C(1) bond length of 2.093(4) Angstrom. The silver complex 2 was reacted with [PdCl2(COD)] to yield the corresponding mono-carbene-palladium complex 3, for which an X-ray diffraction study established a distorted square planar configuration with the imidazolyl and the oxazolinyl ring lying in the molecular plane. The palladium complex 3 was found to be an active catalyst for the Heck and. Suzuki C - C coupling reactions. The coupling of activated or deactivated bromoarenes proceeded rapidly even with a low catalyst loading (0.02 mol %), while the reaction with activated chloroarenes required a higher catalyst loading of 3 mol.