Water-Soluble Palladium(II) Complexes with Sulfonated N-Heterocyclic Carbenes in Suzuki Cross-Coupling and Hydrodehalogenation Reactions

Water-soluble Pd(II) complexes of general formula Na-x[(NHC)PdCl2L] (L = Cl- (1), PPh3 (2), PPh2(C6H4-m-SO3Na) (3), and 4-Mepy (4)), where NHC is a dianionic sulfonated and sterically hindered N-heterocyclic carbene, have been prepared. The new complexes are active catalysts for the Suzuki-Miyaura cross-coupling of aryl chlorides and boronic acids in mixtures of isopropyl alcohol/water or, in the case of water-soluble aryl chlorides, in pure water. The trichloride complex 1, the crystal structure of which is reported, catalyzes the coupling of inactivated and sterically hindered substrates under mild conditions (60 degrees C, 0.1 mol % Pd). The corresponding biphenyls are obtained in almost quantitative yields, except in the case of some of the most hindered aryl chlorides, for which small amounts of arene are also formed by a competitive hydrodehalogenation process.