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

Abstract

The reactivity of a series of gold(III) adducts [Au(HL)Cl₃] 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 [Au₂(HL)₂(µ-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 4b[PF₆]₂, solved by X-ray diffraction, shows that the cation is a centrosymmetric dimer with two oxo (O^2–) 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.