Enantiomerically Pure [M₆L₁₂] or [M₁₂L₂₄] Polyhedra from Flexible Bis(Pyridine) Ligands

Abstract

Coordination-driven self-assembly is one of the most powerful strategies to prepare nanometer-sized discrete (supra)molecular assemblies. Herein, we report on the use of two constitutionally isomeric BINOL-based bis(pyridine) ligands for this purpose. Upon coordination to Pd(II) ions these self-assemble into enantiomerically pure endo- and exo-functionalized hexa- and dodecanuclear metallosupramolecular spheres with a chiral skeleton depending on the substitution pattern of the BINOL core. These aggregates were characterized by NMR, MS, DLS, TEM, and EELS as well as ECD. Furthermore, experimental ECD data could be compared to those obtained from theoretical simulations using a simplified Tamm-Dancoff approximation to time-dependent DFT to rationalize the extraordinary high molar circular dichroisms. Despite the rotational freedom around the central aryl-aryl bond of these ligands, the self-assembly process happens completely selective in a "narcissistic" self-recognition manner.

Ni3 versus Ni30: A Truncated Octahedron Metal–Organic Cage Constructed with [Ni5(CN)4]6+ Squares and Tripodal Tris‐tacn Ligands That are Large and Flexible

“…For each [Ni 5 (CN) 4 ] 6 + square, four Ni atoms reside at the four corners of as quarep lanar,a nd they are bridged together through a m 4 - Ni(CN) 4 unit ( Figure 2C). [33][34][35] The centralN ia tom is coordinated by four cyanidei ons via the Ca toms and is bound to an additional axial chloride ligand,g iving as quare pyramid geometry.T he average NiÀC distance is 1.858(12) ,a nd the average NiÀCl distance is 2.856 (15) .B ased on comparison of this NiÀCd istance to many others reported in [Ni(CN) 4 ] 2À units, [36] this Ni atom has ad 8 Ni II electronic structure. Allt hese resultsa re consistent with triply-bonded groups.A si ti sn ot likely to form CC groups under the synthetic conditions, we assigned them as cyanidei ons, which could be generated in situ via Ni-catalyzed CÀCN bond cleavage of acetonitrile.…”

“…For m 2 -h 1 ,h 1 -groups linking the central and corner Ni atoms, we assigned them as cyanidei ons based on (1) they are two-atom units with al inear bridging mode and (2) the bond lengths of 1.154(13) (by average) between the two atoms are very short. The averageC ÀNiÀCb ond angle of 89.788 shows that the Ni atom is located almost perfectly at the center of the squarep lanar.F or the four corner Ni atoms, each is coordinated by at acn moietyo ft he ligand arm throught hree Na toms,a nd is bound to the Na tom of the bridging cyanide group.The octahedral coordination geometry of these corner Ni atoms is filled by two additional aqua ligands.B VS calculation of 2.29 suggests d 8 Ni II electronic structures for these corner Ni atoms. Such bond activations have been investigated in detail by Jones and co-workerse xperimentally and theoretically,w ho demonstrated that Ni complexes were able to catalyze the CÀCN bond cleavage of various organic nitrile complexes.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] The constructiono fm etalorganic cages is realizedb yt he self-assembly of metal ions or metal clusters typicallyo ccupying the vertices of ad iscrete polyhedron and organic ligands linking them as either the edges or the faces of the polyhedron. [1][2][3][4][5][6][7][8][9][10][11][12] The constructiono fm etalorganic cages is realizedb yt he self-assembly of metal ions or metal clusters typicallyo ccupying the vertices of ad iscrete polyhedron and organic ligands linking them as either the edges or the faces of the polyhedron.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] The constructiono fm etalorganic cages is realizedb yt he self-assembly of metal ions or metal clusters typicallyo ccupying the vertices of ad iscrete polyhedron and organic ligands linking them as either the edges or the faces of the polyhedron. [8] Therefore, molecular metal-organic cages using building blockso fh igh-nuclearity metal clusters as vertices and flexible ligandsasl inkages are scarcely reported in the literature. On the other hand, rigid linear/bent or facial ligands with preorganized binding angles are usually required for the assembly of cages because ligands of flexible conformation and binding ability generally result in mixed coordination species.…”

Synthesis and Characterization of Self‐Assembled Chiral FeII2L3 Cages

“…[20] BINOL-based buildingb locks have also been investigated as chiral units for the construction of supramolecular chiral structures. [21][22][23][24][25][26] In this contribution, we report BINOL-based building blocks for the construction of Fe II 2 L 3 -type cages by using the typical Nitschke subcomponent self-assembly strategy.V arious Fe II 2 L 3 cages were prepared, and within this series, the extent to which the chiral informationa tt he BINOL building blocks could be transferred to the coordination centers was evaluated. We concludet hat enantiopure single-isomer cages only form if, next to the BINOL building blocks, chiral amines are used to steer the chirality at the coordination complexes aroundiron.…”