Chelating and ‘pincer’ dicarbene complexes of palladium; synthesis and structural studies

Abstract

A series of ‘pincer’ 2,6-pyridyl dicarbene complexes of the type [(C–N–C)PdX]⁺, 4a, 4b, 2,6-lutidinyl dicarbene complexes of the type [(C⁁N⁁C)PdX]⁺, 4c, 4d, 1,3-xylyl dicarbene complexes of the type [(C⁁C⁁C)PdX], 5a,5b,5c and 1,2-xylyl dicarbene complexes [(CC)PdX₂], 8, where carbene is 3-arylimidazol-2-ylidene, aryl = mesityl, 2,6-Prⁱ₂C₆H₃, X = Br or Cl, have been prepared by (i) transmetallation from the corresponding silver complexes, i.e. [(C–N–C)Ag₂Cl₂], [(C⁁N⁁C)Ag₂Cl₂] and [(CC)Ag₂Cl₂] to palladium, (ii) substitution of cod in (cod)PdX₂ by the ‘pincer’ (C–N–C) (iii) palladation of bis-imidazolium salts [C(H)⁁C(H)⁁C(H)] in the presence of base. The crystal structures show that the ligands act as chelates in 4–5, while in 8 as both chelate and bridging.