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'-bipyridinesH L (N2C10H7RR, = CH,Ph, CHMePh, CMe,Ph,
CH,Me, CMe, or CH,CMe,) with HAuC1, or Na[AuCl,] has been investigated. Under different experimental
conditions, salts [H,L][AuCI,], adducts [Au(HL)Cl,] or cyclometallated derivatives [Au(L)Cl]m] (X =
AuCl,, BF4 or PF,) 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{N,CloH7(CHMePh)-6}C13]
and two metallated species [Au{N,C,oH7(CMe,C,H,)-6}Cl][AuCl,] and [Au{N2CloH7(CMe2CH2)-
6}CI][BF4]~0.5H20 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) A. 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{N,CloH7(CMe2C6H,)-6}~~]t+h e
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 9 H 2.62 A. The pentaatomic N,C ring
in [Au{N2CloH7(CMe2CH,)-6)Cll + 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.