Pyrazole-tethered phosphine ligands for Pd(0): useful catalysts for Stille, Kumada and Hiyama cross-coupling reactions

Combination of 3,5-dimethyl-1-(2-(diphenylphosphino)phenyl)-1H-pyrazole, A, and 3-tert-butyl-5-methyl-1-(2-(diphenylphosphino)phenyl)-1H-pyrazole, B, with Pd2(dba)3 furnished excellent catalysts for Stille, Kumada and Hiyama cross-coupling reactions. Effects of solvents, bases and ligand/palladium ratio on efficiency of coupling reactions were studied. Molecular structures of palladium(II) complexes of A and B determined by single-crystal X-ray diffraction method revealed a close similarity of ligand arrangement around the metal centre.