Hierarchical self-assembly of dendritic macromolecules via weak interactions such as H-bonding forces 1 has attracted great attention for the design of well-defined mesoscopic materials and also in relation to self-organization events in natural systems. For example, Percec and co-workers have reported that a carboxylic acid-anchored poly(benzyl ether) dendron having long alkyl chains at the periphery self-assembles via H-bonding and van der Waals interactions to form a cylindrical columnar assembly, 2 which can be regarded as a primary synthetic model of icosahedral viruses. 3 Recently, we have reported that a poly(benzyl ether) dendron anchoring a H-bonding dipeptide core self-assembles to form micrometer-scale fibers to induce efficient gelation of various organic solvents. 4 Herein we report results of the first study on utilization of weak metal-metal interactions among group 11 metal ions 5 for hierarchical self-organization of dendritic macromolecules (Chart 1). 6 For this purpose, we chose pyrazole as the metal-ligating module, which is an exobidentate ligand capable of forming coordination metallacycles with Cu(I), Ag(I), and Au(I). 7,8 X-ray diffraction studies have suggested that they form in the solidstate long columnar assemblies involving a weak metal-metal interaction. 8d More recently, pyrazoles having long alkyl chains, in the presence of Au(I), have been reported to form discotic liquid crystalline materials 9 via an edge-to-edge zigzag stacking of the metal pyrazolate coordination triangles. 9b A series of pyrazole-anchored poly(benzyl ether) dendrons (LnPZ, Chart 1) with different generation numbers (n [number of alkoxybenzyl layers] ) 2-4) were synthesized by the reaction of acetylacetone derivatives of the corresponding dendrons 10 with hydrazine. 11 Metal pyrazolate complexes of LnPZ with group 11 metal ions were prepared according to a literature method 7a,9a with partial modification and unambiguously characterized. 11 For example, the IR spectrum of the Au(I) complex of L2PZ (KBr pellet) showed a vibrational band at 1517 cm -1 assignable to a metal-coordinated NdC bond 8d,9a,12 without any N-H stretching vibrational band at 3200-3000 cm -1 . 1 H NMR spectrum in CDCl 3 of L2PZ, upon coordination with Au(I), showed a slight downfield shift (∆δ ) 0.03 ppm) of the signal due to the pyrazole methyl groups. 11 In size-exclusion chromatography (SEC) of the complex, a single, sharp elution peak was observed at a higher molecular weight region than L2PZ. 11 Although the complexation of pyrazole with group 11 metal ions is known to form linear coordination polymers in the solid state, 13 the absence of any polydisperse character in the SEC profile, together with the simplicity of the 1 H NMR spectrum, indicates that the Au(I) complex adopts a uniformly sized, highly symmetric cyclic structure. MALDI-TOF-MS analysis showed a single peak centered at 2144, which corresponds to a trimer of Au(L2PZ) ([Au(L2PZ)] 3 ; [M + H + ] calcd 2144). 11 [Au(L2PZ)] 3 was highly robust toward protonolysis with wat...
