Synthesis and Characterization of Gold(III) Adducts and Cyclometallated Derivatives with 2-Substituted Pyridines. Crystal Structure of [Au{NC5H4(CMe2C6H4)-2}Cl2]

The 2-benzylpyridines HL [NC,H,-(CH,Ph)-2, -(CHMePh)-2 and (CMe,Ph)-21 reacted with Au- CI,.2H20 or Na[AuCI,] to give adducts [Au( HL)CI,] or cyclometallated derivatives [AuLCI,]. The metallation reaction involves direct activation of a C-H bond of the phenyl substituent. With the 2- alkylpyridines NC,H,(CMe,)-2 and NC,H,(CH,CMe,) -2 (HL) only the tetrachloroaurate(iii) salts [H,L] [AuCI,] were isolated. The structure of [Au{NC,H,(CMe,C,H,) -2}CI,] 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) A. The cyclometallated species react with PPh, to give cationic complexes [AuL( PPhJCI] + and with 1,2-bis(diphenylphosphino)ethane (dppe) to yield [AuL(dppe)CI] +. 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.