Liquid-crystalline self-organization of isocyanide-containing dendrimers induced by coordination to gold(I) fragments

Article abstract of DOI:10.1021/ja909435e

Dendritic polyisocyanides can be considered as promising polytopic ligands to generate a great diversity of metallodendrimers due to the ability of the isocyanide moiety to bind to various transition metals. Here, new isocyanide-containing dendrimers and their corresponding polynuclear gold complexes have been prepared, [Gⁱ(NC)_Z] and [G ⁱ(NCAuR)_Z], respectively, where Gⁱ is a poly(phenyl ether) dendrimer, i is the generation number (i = 0, 1, or 2), Z is the number of peripheral groups (Z ) 3 x 2ⁱ), and AuR are the surface groups ([R ) Cl, C≡C-C₆H₄-OC₁₂H ₂₅, C≡CC₆H₂(OC₁₂H ₂₅)3]. The compounds are derived from a highly flexible phenyl ether-based dendritic core, Gi, having the general formula G⁰ = C₆H₃(OC₁₁H₂₂OC₆H _4-)₃, G¹ ) C₆H₃[OC ₁₁H₂₂OC₆H₃(OC₁₁H ₂₂OC₆H_4-)₂]₃, G ² = C₆H₃[OC₁₁H₂₂OC ₆H₃{OC₁₁H₂₂OC₆H ₃(OC₁₁H₂₂OC_6- H_4-) ₂}₂]₃), growing from the trivalent phloroglucinol and with undecylene aliphatic spacers between each branching benzene ring and end-functionalized by isocyanide groups. As in their monomeric model counterparts, stable liquid-crystalline phases are induced upon complexation of the AuR gold moieties at the branch termini. The nature of the anionic ligand R promotes the appearance of smectic or columnar mesophases, the formation of which are governed by steric and dipolar interactions. Based on X-ray diffraction experiments, models describing the supramolecular organization of these metallodendrimers into smectic and columnar mesophases are proposed: columnar phases result from the one-dimensional stacking of molecular disks made of self-assembled supermolecules in oblate cylindrical conformation, while the smectic phases form by the lateral two-dimensional registry of the supermolecules in antiparallel head-to-head prolate conformation.