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

Abstract

The reaction of a series of 6-substituted-2,2′-bipyridines HL (N₂C₁₀H₇R, R = CH₂Ph, CHMePh, CMe₂Ph, CH₂Me, CMe₃ or CH₂CMe₃) with HAuCl₄ or Na[AuCl₄] has been investigated. Under different experimental conditions, salts [H₂L][AuCl₄], adducts [Au(HL)Cl₃] 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}Cl₃] and two metallated species [Au{N₂C₁₀H₇(CMe₂C₆H₄)-6}Cl][AuCl₄] and [Au{N₂C₁₀H₇(CMe₂CH₂)-6}Cl][BF₄]·0.5H₂O 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)Å. 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(CMe₂C₆H₄)-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 ⋯ H 2.62 Å. The pentaatomic N,C ring in [Au{N₂C₁₀H₇(CMe₂CH₂)-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.