Triple helicates with golden strands: self-assembly of M2Au6 complexes from gold(I) metallaligands and iron(II), cobalt(II) or zinc(II) cations.

ABSTRACT

Alkynyl gold(I) metallaligands [(AuC≡Cbpyl)2(µ-diphosphine)] (bpyl=2,2'-bipyridin-5-yl; diphosphine=Ph2P(CH2)(n)PPh2, [n=3 (L(Pr)), 4 (L(Bu)), 5 (L(Pent)), 6 (L(Hex))], dppf (L(Fc)), Binap (L(Binap)) and Diop (L(Diop))) react with MX2 (M=Fe, Zn, X=ClO4; M=Co, X=BF4) to give triple helicates [M2(L(R))3]X4. These complexes, except those containing the semirigid L(Binap) metallaligand, present similar hydrodynamic radii (determined by diffusion NMR spectroscopy measurements) and a similar pattern in the aromatic region of their (1)H NMR spectra, which suggests that in solution they adopt a compact structure where the long and flexible organometallic strands are folded. The diastereoselectivity of the self-assembly process was studied by using chiral metallaligands, and the absolute configuration of the iron(II) complexes with L(Binap) and L(Diop) was determined by circular dichroism spectroscopy (CD). Thus, (R)-L(Binap) or (S)-L(Binap) specifically induce the formation of (Δ,Δ)-[Fe2((R)-L(Binap))3](ClO4)4 or (Λ,Λ)-[Fe2((S)-L(Binap))3](ClO4)4, respectively, whereas (R,R)- or (S,S)-L(Diop) give mixtures of the ΔΔ- and ΛΛ-diastereomers. The ΔΔ helicate diastereomer is dominant in the reaction of Fe(II) with (R,R)-L(Diop), whereas the ΛΛ isomer predominates in the analogous reaction with (S,S)-L(Diop). The photophysical properties of the new dinuclear alkynyl complexes and the helicates have been studied. The new metallaligands and the [Zn2(L(R))3](4+) helicates present luminescence from [π→π*] excited states mainly located in the C≡Cbpyl units.