Synthesis and characterization of gold(III) adducts and cyclometallated derivatives with 2-substituted pyridines. Crystal structure of [Au{NC5H4(CMe2C6H4)-2}Cl2]
Abstract
The 2-benzylpyridines HL [NC5H4-(CH2Ph)-2, -(CHMePh)-2 and (CMe2Ph)-2] reacted with AuCl3·2H2O or Na[AuCl4] to give adducts [Au(HL)Cl3] or cyclometallated derivatives [AuLCl2]. The metallation reaction involves direct activation of a C–H bond of the phenyl substituent. With the 2-alkylpyridines NC5H4(CMe3)-2 and NC5H4(CH2CMe3)-2 (HL) only the tetrachloroaurate(III) salts [H2L][AuCl4] were isolated. The structure of [Au{NC5H4(CMe2C6H4)-2}Cl2] has been determined by X-ray diffraction. It reveals a six-membered ring having a boat-like conformation: there is a rather short interaction between one hydrogen of the Me group in axial position and the gold atom, Au ⋯ H 2.56(5)Å. The cyclometallated species react with PPh3 to give cationic complexes [AuL(PPh3)Cl]+ and with 1,2-bis(diphenylphosphino)ethane (dppe) to yield [AuL(dppe)Cl]+. Under pressure (50 atm, 60 °C) of CO extrusion of the metal occurs. The organic products formed likely arise from insertion of CO into the Au–C bond. The reactivity of the cycloaurated species is compared with that of analogous palladium(II) derivatives described previously.