Incorporation of 2,6-Di(4,4‘-dipyridyl)-9-thiabicyclo[3.3.1]nonane into Discrete 2D Supramolecules via Coordination-Driven Self-Assembly

Dual-Emissive Rectangular Supramolecular Pt(II)-p-Biphenyl with 4,4'-Bipyridine Derivative Metallacycles: Stepwise Synthesis and Photophysical Properties

Mixed-ligand tetranuclear supramolecular coordination complexes (SCCs) of Pt(II)-p-biphenyl and bridging ligands derivatives of 4,4'-bypiridine (8)-(10), were synthesized and characterized. The SCCs were synthesized stepwise, starting from the Pt-p-biphenyl -Pt core. The crystal structure of complex {[Pt(2,2'-bpy)]4(μ-bph)2(μ-(4,4'-bpy)2}{PF6}4 (2,2'-bpy = 2,2'-bipyridine, bph = p-biphenyl and 4,4'-bpy = 4,4' bipyridine), was determined using single-crystal diffraction methods. The emission profile of the tetranuclear complexes (8)-(10) was influenced by the length of the bridging ligands and was found to depend on solvent polarity. Dual-emission patterns in methanol-water mixtures were observed only in the cases of complexes (9) and (10), attributed to aggregation-induced emission phenomena.

Trefoiled Propeller-Shaped Spiral Terpyridyl Metal-Organic Architectures

Constructing exquisite and intricate molecular architectures is always the pursuit of chemists. In this report, the propeller-shaped trefoil structures S1 and S2 were successfully prepared by the stepwise self-assembly of predesigned tripodal metal-organic ligands, which consist of bis(terpyridine)s-Ru²⁺-tris(terpyridine)s connectivities for the following complexation with Fe²⁺. The complexes can be described as racemic spiral assemblies with three-fold spiralism. These unique discrete metal-organic architectures were fully characterized by ¹H NMR, 2D NMR spectroscopy (COSY and NOESY), diffusion-ordered NMR spectroscopy (DOSY), ESI-MS, TWIM-MS, and TEM, and their photophysical and electrochemical properties were also investigated. Further, hybrid trefoiled structure [Fe₃L1L2] was detected by taking advantage of the flexibility of metal-organic ligands.

Geometrically Complementary Self-Assembly of a Hexarhomboid Architecture from Two Ruthenium(II)-Organic Building Blocks

A shape-persistent metallosupramolecular multirhomboid that inlays a hexarhomboid polygon in a three-lobed flat structure was prepared by means of coordination-driven self-assembly. The key ligands were synthesized by a "reaction on complex" strategy that becomes accessible to troublesome metalloorganic ligand L3. The formation here consists of four different starting components and two metal ions. Complementarity of the shape and size drives molecular puzzling and results in the multicomponent, quantitative self-assembled construct.

Conformer-dependent self-assembled metallacycles with photo-reversible response

Discrete, well-defined metallacycles and metallacages with stimuli-responsive behaviors have been largely predominated by the organic donor/metal acceptor paradigm with spontaneous formation of coordination bonds. However, light-driven self-assembly systems usually show relatively low utilization yield of photons and low fatigue resistance. Given that almost no example illustrates the different self-assembly behaviors of antiparallel and parallel conformers in the traditional photochromic diarylethene (DAE) system, here we have for the first time constructed a unique series of photoactive conformer-dependent metallacycles, focusing on the characterization and comparison of self-assembly behavior in different ligand conformers with different di-platinum(ii) acceptors. Their photoswitchable scaffold sizes and shapes are precisely controlled by photochromically separable parallel or anti-parallel conformers via coordination-driven self-assembly. The ap-conformer and closed form provide larger bending angles upon coordination with di-Pt(ii) acceptors into hexagon [6 + 6] or [3 + 3] while the p-conformer only can form smaller polygon cycles. Notably, in contrast with the non-photoactive parallel conformer, the reversible interconversion of anti-parallel ring-open and ring-closed conformer metallacycles can be achieved by alternate irradiation with UV and visible light, respectively, along with a relatively high conversion ratio and good fatigue resistance. This work provides a potential way to construct smart materials for use in sensing, catalysis and drug delivery systems.

Recent advances in the construction of fluorescent metallocycles and metallocages via coordination-driven self-assembly

During the last few years, the construction of fluorescent metallocycles and metallocages has attracted considerable attention because of their wide applications in fluorescence detection of metal ions, anions, or small molecules, mimicking complicated natural photo-processes, and preparing photoelectric devices, etc. This perspective focuses on the recent advances in the construction of a variety of fluorescent metallocycles and metallocages via coordination-driven self-assembly. In addition, the fluorescence properties and the applications of these organometallic architectures have also been discussed.

Self-Assembly of Coordinative Supramolecular Polygons with Open Binding Sites

The design and synthesis of coordinative supramolecular polygons with open binding sites is described. Coordination-driven self-assembly of 2,6-bis(pyridin-4-ylethynyl)pyridine with 60° and 120° organoplatinum acceptors results in quantitative formation of a supramolecular rhomboid and hexagon, respectively, both bearing open pyridyl binding sites. The structures were determined by multinuclear ((31)P and (1)H) NMR spectroscopy and electrospray ionization (ESI) mass spectrometry, along with a computational study.

Nanometer-scale water-soluble macrocycles from nanometer-sized amino acids

This paper introduces the unnatural amino acids m-Abc(2K) and o-Abc(2K) as nanometer-sized building blocks for the creation of water-soluble macrocycles with well-defined shapes. m-Abc(2K) and o-Abc(2K) are homologues of the nanometer-sized amino acid Abc(2K), which we recently introduced for the synthesis of water-soluble molecular rods of precise length (J. Am. Chem. Soc. 2007, 129, 7272). Abc(2K) is linear (180 degrees), m-Abc(2K) creates a 120 degree angle, and o-Abc(2K) creates a 60 degree angle. m-Abc(2K) and o-Abc(2K) are derivatives of 3'-amino-(1,1'-biphenyl)-4-carboxylic acid and 2'-amino-(1,1'-biphenyl)-4-carboxylic acid, with two propyloxyammonium side chains for water solubility. m-Abc(2K) and o-Abc(2K) are prepared as Fmoc-protected derivatives Fmoc-m-Abc(2K(Boc))-OH (1a) and Fmoc-o-Abc(2K(Boc))-OH (1b). These derivatives can be used alone or in conjunction with Fmoc-Abc(2K(Boc))-OH (1c) as ordinary amino acids in Fmoc-based solid-phase peptide synthesis. Building blocks 1a-c were used to synthesize macrocyclic "triangles" 9a-c, "parallelograms" 10a,b, and hexagonal "rings" 11a-d. The macrocycles range from a trimer to a dodecamer, with ring sizes from 24 to 114 atoms, and are 1-4 nm in size. Molecular modeling studies suggest that all the macrocycles except 10b should have well-defined triangle, parallelogram, and ring shapes if all of the amide linkages are trans and the o-alkoxy substituents are intramolecularly hydrogen bonded to the amide NH groups. The macrocycles have good water solubility and are readily characterized by standard analytical techniques, such as RP-HPLC, ESI-MS, and NMR spectroscopy. (1)H and (13)C NMR studies suggest that the macrocycles adopt conformations with all trans-amide linkages in CD(3)OD, that the "triangles" and "parallelograms" maintain these conformations in D(2)O, and that the "rings" collapse to form conformations with cis-amide linkages in D(2)O.

Construction of coordination-driven self-assembled [5 + 5] pentagons using metal-carbonyl dipyridine ligands

The coordination-driven self-assembly of two metal-carbonyl-cluster-coordinated dipyridyl donors, (4-C(5)H(4)N)(2)C[triple bond]CCo(2)(CO)(6) (1) and (4-C(5)H(4)N)(2)C[triple bond]CMo(2)Cp(2)(CO)(4) (2), with a linear diplatinum(II) acceptor ligand was investigated. The structures of the resulting self-assembled polygons were found to be controlled by the steric bulk of the metal-carbonyl cluster adduct. The use of a sterically less imposing ligand 1 resulted in a pentagon-hexagon mixture, which was characterized by electrospray ionization time-of-flight mass spectroscopy. The exclusive formation of a [5 + 5] pentagon was achieved by the self-assembly of the bulkier molybdenum donor ligand 2 with a linear organoplatinum(II) acceptor ligand. Molecular force field modeling was used to study the structural details of the pentagonal and hexagonal architectures. The first Fe(3)-Co(6)-Pt(6) trimetal [3 + 3] hexagon was also synthesized via the combination of 1 with a 120 degrees ferrocenyldiplatinum(II) acceptor.

From solvolysis to self-assembly

My sojourn from classical physical-organic chemistry and solvolysis to self-assembly and supramolecular chemistry, over the last forty years, is described. My contributions to unsaturated reactive intermediates, namely vinyl cations and unsaturated carbenes, along with my decade-long involvement with polyvalent iodine chemistry, especially alkynyliodonium salts, as well as my more recent research with metal-ligand, coordination driven, and directed self-assembly of finite supramolecular ensembles are discussed.

Supramolecule-to-supramolecule transformations of coordination-driven self-assembled polygons

Two types of supramolecular transformations, wherein a self-assembled Pt(II)-pyridyl metal-organic polygon is controllably converted into an alternative polygon, have been achieved through the reaction between cobalt carbonyl and the acetylene moiety of a dipyridyl donor ligand. A [6 + 6] hexagon is transformed into two [3 + 3] hexagons, and a triangle-square mixture is converted into [2 + 2] rhomboids. 1H and 31P NMR spectra are used to track the transformation process and evaluate the yield of new self-assembled polygons. Such transformed species are identified by electrospray ionization (ESI) mass spectrometry. This new kind of supramolecule-to-supramolecule transformations provides a viable means for constructing, and then converting, new self-assembled polygons.

Coordination-driven self-assembly of cavity-cored multiple crown ether derivatives and poly[2]pseudorotaxanes

The synthesis of a new 120 degree diplatinum(II) acceptor unit and the self-assembly of a series of two-dimensional metallacyclic polypseudorotaxanes that utilize both metal-ligand and crown ether-dialkylammonium noncovalent interactions are described. Judiciously combining complementary diplatinum(II) acceptors with bispyridyl donor building blocks, with an acceptor and/or donor possessing a pendant dibenzo[24]crown-8 (DB24C8) moiety, allows for the formation of three new rhomboidal bis-DB24C8, one new hexagonal tris-DB24C8, and four new hexakis-DB24C8 metallacyclic polygons in quantitative yields. The size and shape of each assembly, as well as the location and stoichiometry of the DB24C8 macrocycle, can be precisely controlled. Each polygon is able to complex two, three, or six dibenzylammonium ions without disrupting the underlying metallacyclic polygons, thus producing eight different poly[2]pseudorotaxanes and demonstrating the utility and scope of this orthogonal self-assembly technique. The assemblies are characterized with one-dimensional multinuclear ((1)H and (31)P) and two-dimensional ((1)H-(1)H COSY and NOESY) NMR spectroscopy as well as mass spectrometry (ESI-MS). Further analysis of the size and shape of each assembly is obtained through molecular force-field simulations. (1)H NMR titration experiments are used to establish thermodynamic binding constants and poly[2]pseudorotaxane/dibenzylammonium stoichiometries. Factors influencing the efficiency of poly[2]pseudorotaxane formation are discussed.