Self‐Assembly of a Supramolecular, Three‐Dimensional, Spoked, Bicycle‐like Wheel

Abstract

The function and properties of materials and biological organisms are not only related to the chemical structure and connectivity, but also through higher-order domain structure, such as in the magnetic domain of magnetic materials [1] as well as the secondary and tertiary structures of proteins and DNA. [2] Weak interactions such as hydrogen bonding and coordination exist widely in biological systems and are vital for biological metabolism and many other essential functions. [3] These supramolecular interactions [4] have attracted attention both in biology [5] as well as in numerous other fields, [6] such as supramolecular catalysis, chemical sensing, and molecular electronics. [7] 2,2':6',2''-Terpyridine (tpy) has been a widely used ligand for the creation of such motifs, partly because of its ability to coordinate diverse metals. There are numerous examples of tpy-based supramolecular systems, from 2D-based macrocycles and grids [8] to 3D arrangements, such as cages and prisms. [9] A two-dimensional, tpy-based supramolecular spoked wheel was previously reported. [10] In this three-component ensemble, two different terpyridine ligands and one type of metal were self-assembled. This 2D wheel structure is more rigid than macrocyclic hexagons because of its fixed spacefilling centerpiece, which also serves as a template for the outer ligands. Notably, very few supramolecular spokedwheel systems have been reported, [10,11] since the self-assembly of multiple components can be a synthetic challenge that requires more precise control over the geometry and connectivity. [12] To further functionalize the well-established tpy-based spoked-wheel assembly, the backbone and connectivity components of its original structure were redesigned. The framework, in this case, includes two parts: the spokes (S3) and rims (R3; core and outer ligands, respectively; numbers equate to the available tpy units). The core that originally consisted of the single, hexakis(terpyridine) S6 was replaced by two aromatic cores functionalized with three terpyridine ligands at 1208 that adopt a staggered conformation (Scheme 1). Thus, the new construct involves the two tris(terpyridine)s S3, six rim units R3 in which the three tris(terpyridine)s are separated by angles of 608, and twelve metals in a precise 2:6:12 ratio, respectively. The two central tris-tpy ligands are stacked with a common perpendicular axis to impart the 3D bicycle-wheel motif. b-Glucose moieties were attached to the tris-tpy rim component R3 to increase the solubility of the desired complex.The synthesis of rim ligand R3 (Scheme 2) started with bromination of 2,6-dimethoxyphenol to afford 1, followed by etherification with benzyl bromide to give 2. Next, 3 was prepared (67 %) through a Suzuki cross-coupling reaction between 2 and 4'-boronatophenyl-2,2':6',2''-terpyridine [13] by utilizing [PdCl 2 (PPh 3 ) 2 ] as a catalyst. The benzyl group in 3 was removed with ammonium formate in the presence of a Pd/C catalyst to afford 4, which underwent alkylation with N-(6-bromohe...

Order from Chaos: Self‐Assembly of Nanoprism from a Mixture of Tetratopic Terpyridine‐Porphyrin Conformers

“…2D‐DOSY spectra of S1 and S2 (Figures e and f) display single narrowly distributed signal bands with diffusion coefficients ( D ) around 1.2 × 10 –9 m 2 ·s –1 ( S1 ) and 1.0 × 10 –9 m 2 ·s –1 ( S2 ), respectively, further confirming the isomeric purity of the assemblies. More detailed analysis of the 1 H NMR spectra of L2 and S2 , for instance, shows characteristic downfield shift of H f ( δ ~0.05) and obvious upfield shift of H j ( δ ~1.0) after coordination, due to the electron deficiency of H f and the electron shielding effect of H j by the zinc ions, respectively. In addition, the shifts of the protons on the phenyl spacer after coordination were observed.…”

Group 8 Metallomacrocycles – Synthesis, Characterization, and Stability

“…[2] Metal-ligand-promoted self-assembly utilizing the N-heteroaromatic ligand, 2,2Ј:6Ј,2ЈЈ-terpyridine (tpy), has received increasing attention [3] due to its ability to coordinate with a wide variety of transition metals, thus enabling a range of bonding strengths, properties, and molecular architectures, [4] such as macrocycles [5,6] and 3D structures. [7][8][9] Of particular interest, due to their light absorption in the visible spectrum, are Ͻtpy-Os II -tpyϾ complexes that possess long-lived metal-to-ligand charge transfer (MLCT) excitations, photoreactivity, and structural stability. [4,10] These characteristics make Ͻtpy-Os II -tpyϾ complexes suitable for a range of functions in artificial photosynthesis including photosensitizers, [10] light harvesting antennae, [11] and bridging [12] of such components into fully integrated artificial photosynthetic molecular architectures.…”

One Ligand in Dual Roles: Self‐Assembly of a Bis‐Rhomboidal‐Shaped, Three‐Dimensional Molecular Wheel

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A facile high yield, self-assembly process that leads to a terpyridine-based, three-dimensional, bis-rhomboidal-shaped, molecular wheel is reported. Hence, the original synthetic route [8] involved a three-component system (Scheme 1): two tritopic ligands to form the central hub (two tris-terpyridine S3 in C1), six tritopic ligands forming the rims (six tris-terpyridine R3 in C1) and twelve metal ions as the linkage. The tpy ligand plays dual roles in the self-assembly process: two are staggered at 1808 to create the internal hub, while six produce the external rim.

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“…Hence, the original synthetic route [8] involved a three-component system (Scheme 1): two tritopic ligands to form the central hub (two tris-terpyridine S3 in C1), six tritopic ligands forming the rims (six tris-terpyridine R3 in C1) and twelve metal ions as the linkage. Hence, the original synthetic route [8] involved a three-component system (Scheme 1): two tritopic ligands to form the central hub (two tris-terpyridine S3 in C1), six tritopic ligands forming the rims (six tris-terpyridine R3 in C1) and twelve metal ions as the linkage.…”

“…Thus, ligand R3 b, [8] (X 1 = OBn, X 2 = OMe, Scheme 1) possessing a benzyloxy group, was utilized to construct the related bis-rhomboidal-shaped C2 b (Figure 1), which was prepared by mixing R3 b and Zn(NO 3 ) 2 ·6 H 2 O in a stoichiometric ratio (2:3) under identical conditions (75 8C in MeOH) as used above. To explore the complicated internally stacked hub region, the central methoxy moiety was replaced with an aryl group, so that the imposed neighboring ring current could be used to assign the adjacent protons and to afford structural insight to the inner core region.…”