C,N-Palladacycles Containing N-Heterocyclic Carbene and Azido Ligands - Effective Catalysts for Suzuki-Miyaura Cross-Coupling Reactions

Abstract

Azido-palladacycles containing C,N-donor and N-heterocyclic carbene ligands, [(C,N-L)Pd(N3)(NHC)] [NHC = IPr; 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene], were prepared from (i) IPr and dinuclear PdII azides, [Pd(mu-N3)(C,N-Ln)]2 [C,N-L1H = N,N'-dimethylbenzylamine; C,N-L2H = 2-(2'-thienyl)pyridine; C,N-L3H = azobenzene; C,N-L4H = 2-(p-tolyl)pyridine], or from (ii) NaN3 and mononuclear PdII chloride, [Pd(Cl)(IPr)(C,N-Ln)], in aqueous solution. The structures of two of these products were determined by X-ray crystallography. The palladacycles showed high catalytic efficiency toward activated and nonactivated aryl bromides (at room temperature) as well as aryl chlorides (at 80 degrees C) in SuzukiMiyaura cross-coupling reactions. In addition, coupling reactions of aryl chlorides using potassium aryl trifluoroborates instead of phenyl boronic acid gave good-to-excellent product yields.