mu-Oxo and alkoxo complexes of gold(III) with 6-alkyl-2,2 '-bipyridines. Synthesis, characterization and X-ray structures

The reactivity of a series of gold(III) adducts [Au(HL)Cl-3] 1a-4a with 6-alkyl-2,2'-bipyridines HL (N2C10H7R, R = CH2Me 1, CHMe2 2, CMe3 3 and CH2CMe3 4) has been studied. The reactions of 1a-4a with silver(I) ions or MeCO2Na afford cationic complexes [Au-2(HL)(2)(mu-O)(2)](2+) 1b-4b (as BF4 or PF6 salts) having the gold atom bonded to the nitrogen atoms of the bipyridine and to two oxygen atoms. The crystal structure of Ib[PF6](2), solved by X-ray diffraction, shows that the cation is a centrosymmetric dimer with two oxo (O2-) groups bridging two [Au{N2C10H7(CH2CMe3)-6}] moieties. In the case of 2a, besides the oxo species, mononuclear ionic derivatives [Au(L*)Cl](-)2*c [HL* = N2C10H7(CMe2OH)-6; BF4, PF6 or AuCl4 salts] have been isolated. The latter complexes contain an unexpected Au-O bond. The spectroscopic data and the crystal structure of 2*c[AuCl4] indicate a tridentate N,N,O behaviour of the ligand which forms a [5,5]-fused ring system.