Stepwise radial complexation of imine groups in phenylazomethine dendrimers

K. Yamamoto, M. Higuchi, S. Shiki, M. Tsuruta, H. Chiba
Nature 2002, 415, 509-511.

Dendrimers are highly branched organic macromolecules with successive layers or ‘generations’ of branch units surrounding a central core. Organic–inorganic hybrid versions have also been produced, by trapping metal ions or metal clusters within the voids of the dendrimers. The unusual, tree-like topology endows these nanometre-sized macromolecules with a gradient in branch density from the interior to the exterior, which can give rise to an energy gradient that directs the transfer of charge and energy from the dendrimer periphery to its coreHere we show that tin ions, Sn2+, complex to the imine groups of a spherical polyphenylazomethine dendrimer in a stepwise fashion. This behaviour reflects a gradient in the electron density associated with the imine groups, with complexation in a more peripheral generation proceeding only after complexation in generations closer to the core has been completed. By attaching an electron-withdrawing group to the dendrimer core, we are able to change the complexation pattern, so that the core imines are complexed last. By further extending this strategy, it should be possible to control the number and location of metal ions incorporated into dendrimer structures, which might find uses as tailored catalysts or building blocks for advanced materials.

Nature, News & View 「One generation at a time」Nature, 415, 487-489(2002)

日本工業新聞 「デンドリマーを使い新材料構築ナノ技術」

神奈川新聞 「ナノ材料の創出に成功」

日刊工業新聞 「電子集積化学デバイス開発」

日本工業新聞 「エネルギー低損失材料」

First Synthesis of Phenylazomethine Dendrimer Ligands and Structural Studies

M. Higuchi, S. Shiki, K. Ariga, K. Yamamoto
J. Am. Chem. Soc. 2001, 123, 4414-4420.

First Synthesis of Phenylazomethine Dendrimer Ligands and Structural Studies

Novel dendritic polyphenylazomethines (DPAs), which consist of a π-conjugated backbone, were synthesized up to the fourth generation by the convergent method via dehydration of aromatic ketones with aromatic amines in the presence of titanium(IV) tetrachloride. The obtained dendrimers, DPA G1−4 (designated as GX, where X is the generation number), show high thermostability (Td10% 521 °C in DPA G4) and high solubility for the common solvents such as chloroform, THF, and DMSO unlike the conventional linear polyphenylazomethines, which have very low solubilities. The DPA G4 molecule was confirmed to have a spherelike structure by GPC measurement and a molecular model based on the crystal structure of DPA G2. Crystal data for DPA G2:  monoclinic space group P21/a, a = 25.352(4) Å, b = 8.577(2) Å, c = 16.151(2) Å, β = 106.25(1)°, V = 3371.6(10) Å3, Z = 2, Dcalc = 1.168 g/cm3, μ(Cu Kα) = 0.536 cm-1, final R = 0.089, and Rw = 0.287. The molecular modeling reveals that a DPA G4 molecule has a spherelike structure, in which the height, width, and depth are 2.3, 2.9, and 2.5 nm, respectively. The TEM and AFM pictures show the DPA G4 molecules to have a spherelike structure (the diameter:  2.3 nm) and are regularly assembled on a plate by casting. The occupied area of one DPA G4 molecule in a monolayer on water was estimated by π−A measurements to be 3.8−4.2 nm2 (the calculated diameter 2.2−2.3 nm, which agreed with the TEM result). NMR studies (1H NMR at 130 °C and T1 measurements) supported a conformational rigidity of DPA G4 in solution.