Polypyridyl-functionalizated alkynyl gold(i) metallaligands supported by tri- and tetradentate phosphanes

A series of alkynyl gold(i) tri and tetratopic metallaligands of the type [Au₃(C[triple bond, length as m-dash]C-R)₃(μ₃-triphosphane)] (R = 2,2'-bipyridin-5-yl or C₁₀H₇N₂, 2,2':6',2''-terpyridin-4-yl or C₁₅H₁₀N₃; triphosphane = 1,1,1-tris(diphenylphosphanyl)ethane or triphos, 1,3,5-tris(diphenylphosphanyl)benzene or triphosph) and [Au₄(C[triple bond, length as m-dash]C-R)₄(μ₄-tetraphosphane)] (R = C₁₀H₇N₂, C₁₅H₁₀N₃; tetraphosphane = tetrakis(diphenylphosphanylmethyl)methane or tetraphos, 1,2,3,5-tetrakis(diphenylphosphanyl)benzene or tpbz, tetrakis(diphenylphosphaneylmethyl)-1,2-ethylenediamine or dppeda) were obtained in moderate to good yields. All complexes could be prepared by a reaction between the alkynyl gold(i) polymeric species [Au(C[triple bond, length as m-dash]C-R)]_n and the appropriate polyphosphane. An alternative strategy that required the previous synthesis of the appropriate acetylacetonate precursors [Au_n(acac)_n(μ_n-polyphosphane)] ("acac method") was assayed, nevertheless only the polyacac derivatives [Au₃(acac)₃(μ₃-triphosphane)] (triphosphane = triphos and triphosph) and [Au₄(acac)₄(μ₄-tetraphos)] could be isolated and characterized. All compounds were characterized by IR, multinuclear NMR spectroscopy and ESI(+) mass spectrometry. The X-ray crystal structure of complexes [Au₄(C[triple bond, length as m-dash]C-C₁₀H₇N₂)₄(μ₄-tetraphos)] and [Au₄(C[triple bond, length as m-dash]C-C₁₀H₇N₂)₄(μ₄-tpbz)] showed the involvement of all the gold atoms in close intramolecular AuAu contact as well as intermolecular π stacking interactions between the aromatic rings of the polypyridyl ligands. The photophysical properties of the synthesized compounds were carefully studied and used as a probe of their possible use as multidentate ligands for Cu(i) and Zn(ii). The UV-Vis speciation studies of the complexation reactions were conducted via metal titration and, in most cases the dangling units of the ligand were found to behave in a fairy independent manner. While in the case of Cu(i) multiple equilibria exist in solution a single complex is detected for Zn(ii) under the conditions studied.