Synthesis and characterization of gold(III) adducts and cyclometallated derivatives with 6-benzyl- and 6-alkyl-2,2'-bipyridines

The reaction of a series of 6-substituted-2,2'-bipyridines HL (N(2)C(10)H(7)R, R = CH(2)Ph, CHMePh, CMe(2)Ph, CH(2)Me, CMe(3) or CH(2)CMe(3)) with HAuCl4 or Na[AuCl4] has been investigated. Under different experimental conditions, salts [H(2)L][AuCl4], adducts [Au(HL)Cl-3] or cyclometallated derivatives [Au(L)Cl][X] (X = AuCl4, BF4 or PF6) have been isolated. The cyclometallated species arise from direct activation of a C-H bond either of a phenyl or a methyl substituent. The structures of an adduct [Au{N2C10H7(CHMePh)-6}Cl-3] and two metallated species [Au{N2C10H7(CMe(2)C(6)H(4))-6}Cl][AuCl4] and [Au{N2C10H7(CMe(2)CH(2))-6}Cl][BF4] . 0.5H(2)O have been determined by X-ray diffraction. In the adduct the gold atom is bonded to the nitrogen atom of the unsubstituted pyridine ring: a long-range interaction with the other nitrogen atom is observed, Au ... N 2.758(4) Angstrom. In the two cyclometallated species the bipyridines act as tridentate N,N,C anions, giving a [5,6] and a [5,5]-fused ring system, respectively. In [Au{N2C10H7(CMe(2)C(6)H4)-6}Cl](+) the hexaatomic N,C ring adopts a boat-like conformation: the structure reveals a rather short interaction between one hydrogen of the Me group in axial position and the gold atom, Au ... H2.62 Angstrom. The pentaatomic N,C ring in [Au{N2C10H7(CMe(2)CH(2))-6}Cl](+) is not planar: the co-ordination around the gold atom is essentially square planar. The new cyclometallated complexes [Au(N,N,C)Cl](+) are compared with those derived from similarly substituted pyridines described previously.