Coordination assembled rings of ferrocene-bridged trisporphyrin with flexible hinge-like motion: selective dimer ring formation, its transformation to larger rings, and vice versa

Ferrocene-bridged trisporphyrin (2) was synthesized by two-steps condensation of corresponding aldehydes and dipyrromethanes, and its self-assembling behavior based on the complementary coordination motif of imidazolylporphyrinatozinc(II) was investigated in conjunction with hinge-like flexibility given by freely rotating cyclopentadienyl rings of ferrocene connector. Ferrocene-bridged trisporphyrin (2) spontaneously and exclusively generated the dimeric ring (7) upon simple zinc(II) insertion, indicating that the freely rotating hinge connector favored the smallest ring formation. Taking advantage of the unique hinge-like flexibility of ferrocene, we attempted to transform the dimer ring into a mixture of porphyrin macrocycles by reorganizing the structure cleaved once by pyridine. A series of porphyrin macrocycles from trimer to decamer can be separated into its components by preparative gel permeation chromatograms. Macrocycles obtained are kept stable in the absence of coordinating solvents. On the other hand, they were easily transformed to the dimer ring in the presence of coordinating solvents such as methanol, showing that the transformation is completely reversible and can be controlled by the choice of the solvent system. A series of porphyrin macrocycles was confirmed via covalent linking of each complementary coordination dimer pair by metathesis reaction in the presence of Grubbs's catalyst. The coordination behavior of the bidentate ligands with different spacer lengths toward the dimer ring revealed that only the bidentate ligand (15) with a spacer length that matched the facing central porphyrins was selectively accommodated inside the ring. Coordination assembled flexible rings with tunable cavities and multiple coordination sites will be used as versatile hosts for a wide variety of guest molecules.     

Novel enantioselective receptors for N-protected glutamate and aspartate

A series of chiral bisthiourea macrocycles 1-4 have been prepared and their binding properties with various dicarboxylate salts have been examined by using NMR titration and isothermal calorimetry experiments. Macrocycle 1, in particular, favours the 1:1 binding of N-protected L-glutamate and aspartate, but favours 1:2 binding of the corresponding D-amino acids in polar solvents (dimethyl sulfoxide and acetonitrile). The macrocycles, however, do not bind carboxylates at all in the less competitive solvent chloroform. The binding properties of these macrocyles are sensitive to small structural changes as demonstrated by the altered binding properties of macrocycles 2-4 compared with 1.     

Pendant-Arm Macrocycles Derived from the Cyclocondensation Reaction of Sodium 2,6-Diformyl-4-substitutedphenolates and Tris-(2-aminoethyl)amine Derivatives. Preparation, Characterization and Properties of their Dinuclear Copper(II) Complexes

A series of pendant-arm Schiff base macrocycles have been obtained via the cyclocondensation reaction between sodium 2,6-diformyl-4-substitutedphenolates and tris-(2-aminoethyl)- amine derivatives followed by transmetallation with Cu(ClO₄)₂·6H₂O. The resulting dinuclear copper(II) complexes have been characterized by elemental analysis, infrared and mass spectra as well as magnetic moments at room temperature. All complexes have been electrochemically investigated, and two typical compounds have been studied with ESR spectra as well.     

A modular "toolbox" approach to flexible branched multimacrocyclic hosts as precursors for multiply interlocked architectures

Tetralactam macrocycles can be functionalized by a variety of cross-coupling reactions. A modular "toolbox" strategy is presented that allows 1) several tetralactam macrocycles to be covalently connected with each other or with a central spacer, 2) the macrocycles to be substituted with or connected to different chromophores, and 3) metal-coordination sites to be attached to the macrocycles. With this approach a series of different oligo-macrocyclic hosts was obtained with great structural diversity and enormous potential for further functionalization. Rotaxanes made on the basis of these macrocycles have been synthesized to demonstrate their utility in building more complex supramolecular architectures.     

Zirconocene-mediated, high-yielding macrocyclizations of silyl-terminated diynes

A series of silyl-terminated diynes of varying lengths and substitution patterns have been prepared. These diynes undergo zirconocene coupling with selective formation of trimeric macrocycles from linear alkynes, while nonlinear diynes give cyclodimeric products. The length of the linear diynes can be increased for the preparation of macrocycles with large nanoscale cavities. Reaction of the zirconium-containing macrocycles with acid results in the synthesis of metal-free cyclophanes. All of these macrocycles were prepared in multigram quantities, in the absence of high-dilution conditions, to give products in > 75% yield that are easily purified as crystalline solids.     

Design, synthesis, and crystallographic studies of neutral platinum-based macrocycles formed via self-assembly

A series of neutral, platinum-based macrocycles was synthesized from rigid oxygen donor building blocks via self-assembly. The combination of a platinum-based 60 degrees acceptor unit 1 with several linear and angular dicarboxylate bridging ligands afforded hitherto unknown neutral platinum-based supramolecular triangles and rhomboids. In addition, a similar reaction of the diplatinum molecular clip 6 and three different linear dicarboxylates led to the formation of neutral molecular rectangles. Most of the macrocycles were characterized by X-ray single-crystal structure analysis, and, in all cases, NMR spectra were consistent with the formation of single highly symmetrical species.     

Self-assembly, binding, and dynamic properties of heterodimeric porphyrin macrocycles

A series of heterodimeric tetralactam macrocycles have been self-assembled using two kinetically labile zinc porphyrin-pyridine interactions. The stability constants have been determined by UV-vis titrations in CHCl3. The stability constants depend on the degree of preorganization of the linker units connecting the interacting groups. The ability of the self-assembled macrocycles to bind a terephthalamide guest was also investigated. One of the macrocycles was used for the construction of a [2]rotaxane. The dynamic properties of this system provide insight into the exchange mechanisms that operate in complex noncovalent assemblies.     

Synthesis, structure, and computational studies of soluble conjugated multidentate macrocycles

[Chemical reaction: See text] Conjugated, shape-persistent macrocycles based on [3 + 3] Schiff-base condensation are of interest for supramolecular materials. In an effort to develop new discotic liquid crystals based on these compounds, a series of macrocycles with peripheral alkoxy groups of varying length have been prepared. The synthesis and mechanism of formation have been probed by isolation of oligomeric intermediates. A single-crystal X-ray diffraction study of one macrocycle revealed a nonplanar, strongly hydrogen-bonded structure. To our surprise, even with very long substituents, the macrocycles were not liquid crystalline. This has been rationalized by ab initio calculations that indicate the macrocycles are undergoing rotation of the dihydroxydiiminobenzene rings that may not allow a stable discotic liquid crystalline phase. These results provide new insight into the formation and properties of these large macrocycles and may provide guidance to developing stable liquid crystalline materials in the future.     

New 2+2, 3+3 and 4+4 macrocycles derived from 1,2-diaminocyclohexane and 2,6-diformylpyridine

Two new Schiff base macrocycles - a 4+4 condensation product and a meso-type 2+2 condensation product - were obtained in a reaction of trans-1,2-diaminocyclohexane and 2,6-diformylpyridine. Reduction of these compounds led to the corresponding 4+4 and 2+2 macrocyclic amines. The macrocycles were characterised by NMR spectroscopy and electrospray mass spectrometry. The symmetry and stereochemistry of these macrocycles, as well as of new 3+3 and 4+4 diastereomers identified in solution, has been established. X-Ray structures of the 2+2 and 4+4 Schiff base macrocycles confirm the configurations determined on the basis of spectroscopic investigations. The crystal structures reveal that the centres of the square-shaped 4+4 macrocycles form channels as a result of columnar stacking.     

Synthesis, structure and ring-opening polymerization of macrocyclic arylates containing phthalic unit

A series of maerocyclic arylate diraers have been selectively synthesized by an interfacial polyconden-sation of o-phthaloyldichloride with bisphenols A combination of GPC,FAB-MS,1H and 13C NMR unambiguously confirmed the cyclic nature Although single-crystal X-ray analysis of two such macrocycles reveals no severe strain on the cyclic structures,these macrocycles can undergo facile melt polymerization to give high molecular weight polyary-lates.     

Macrocyclic Eu3+ chelates show selective luminescence responses to anions

A series of lanthanide-containing macrocycles, Eu2-Eu5, exhibited unique luminescent responses in the presence of strong hydrogen-bond-accepting anions (F-, CH3COO-, and H2PO4-) in dimethyl sulfoxide. The macrocycles examined herein were designed to include a lanthanide chelate, aromatic spacers that function as antennae, thiourea groups as anion-binding units, and an alkyl or aryl linker between the thioureas that tailors the size and rigidity of the macrocycle. The anion-induced change in the emission intensity (lambda(exc) = 272 nm; lambda(em) = 614 nm) varied across the series of macrocycles and was dependent on the basicity of the anion. The largest luminescence response was observed in Eu(2), whereby the emission increased 77% upon the addition of 8 equiv of fluoride. A change in luminescence was not observed when exciting Eu3+ directly (lambda(exc) = 395 nm) over the course of anion titration experiments with all of the anions studied. These macrocycles contain only slight variations in structure, and insights into the mechanism of the anion interaction have been gained through monitoring of anion titrations via luminescence, absorbance, and luminescence lifetime measurements. In addition, model compounds (2-5) lacking the Eu3+ moiety were synthesized to study the binding pockets of Eu2-Eu5 using absorbance and 1H NMR spectroscopy. These studies indicate that the anions interact with the thiourea moiety of Eu2-Eu5, and the luminescent response is controlled by changes in the morphology of the macrocycle binding pocket.     

Efficient proton-templated synthesis of 18- to 38-membered tetraimino(amino)diphenol macrocyclic ligands: structural features and spectroscopic properties

A whole range of Robson-type tetraiminodiphenol macrocyclic ligands have been prepared as their perchlorate salts [H4L](ClO4)2 in high yield (ca. 90%) by a single-step [2 + 2] condensation reaction between 4-methyl(or tert-butyl)-2,6-diformyl(or diacyl)phenols and alpha,omega-diaminoalkanes (C2-C12) in the presence of acetic acid and NaClO4. The reduction of these 18- to 38-membered macrocyclic salts with NaBH4 have afforded corresponding tetraaminodiphenol macrocycles H2L'. The X-ray crystal structures of two of the tetraiminodiphenol macrocycles with the C2 and C4 lateral chains have been determined, and the optimized configurations for all of the macrocycles have been obtained by molecular mechanics calculations. The macrocycles have been characterized by elemental analysis and by IR, absorption, emission, and NMR spectroscopic study. The protonated tetraiminodiphenol macrocycles exhibit strong fluoroscence in methanol, acetonitrile, and nitromethane and undergo quenching when treated with triethylamine. The neutral macrocycles H2L, isolated by treating [H4L](ClO4)2 with excess of triethylamine, lack luminescence, as do the reduced tetraaminodiphenol macrocycles H2L'. The hydrolytic cleavage of [H4L](ClO4)2 has been studied.     

Synthesis,isolation, characterization,and properties of small-size aromatic macrocycles for poly(arylene ether ketone)s

A series of macrocyclic arylene ether ketone oligomers from 4,4′-difluorobenzophenone, 2,4′-difluorobenzophenone and 1,3-bis(4′-fluorobenzoyl)benzene were prepared via aromatic nucleophilic substitution according to the pseudo-high dilution principle. Small-size aromatic macrocycles were isolated by silica gel column chromatography with cyclohexane/ethyl acetate as eluent. The chemical structures of these small-size macrocycles were characterized by matrix-assisted laser desorption ionization–time-of-flight–mass spectrometry (MALDI–TOF–MS), IR, ¹⁹F-,¹H-, and ¹³C-NMR, and GPC techniques. Molecular chain length and steric hindrance of monomers affected the product compositions. The NMR results show that there are different chemical shifts in the different ring-size macrocyclic poly arylene ether ketones in spite of having the same repeating unit. The crystallizability and thermal properties of small-size arylene ether ketone macrocycles were also investigated by DSC, WAXD, TGA, and the results suggest that the crystallization and thermal properties are related to their intrinsic chemical structures. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1957–1967, 1999     

Theoretical investigations on the geometric and electronic structures of phenylene-acetylene macrocycles.

The geometric and electronic structures of a series of conjugated macrocycles (phenylene-acetylene macrocycles, PAMs) have been studied theoretically with ab initio and semiempirical molecular orbital methods. The ab initio calculations at the HF/6-31G* level demonstrate that the model molecules may have a planar conformation. Bigger macrocycles, for example, 7PAM, 8PAM, and 9PAM, result in several energy minima. The boatlike conformation is the most energetically favored form. Based on the conformational analysis, a novel method for analyzing the ring-strain energy was proposed and used. In view of their potential applications as electronic materials, the electronic structures of a series of PAMs are also investigated. The LUMO-HOMO gaps of the planar PAMs show an odd-even difference behavior. In addition, the HOMOs of the planar species 3PAM, 5PAM, 7PAM, and 9PAM are doubly degenerated.     

Smart macrocyclic molecules: induced fit and ultrafast self-sorting inclusion behavior through dynamic covalent chemistry

A family of macrocycles with oligo(ethylene glycol) chains, 4O, 5O, and 6O, was developed to construct a series of new incorporated macrocycles through dynamic covalent chemistry. These flexible macrocycles exhibited excellent "self-sorting" abilities with diamine compounds, which depended on the "induced-fit" rule. For instance, the host macrocycles underwent conformational modulation to accommodate the diamine guests, affording [1+1] intramolecular addition compounds regardless of the flexibility of the diamine. These macrocycles folded themselves to fit various diamines with different chain length through modulation of the flexible polyether chain, and afforded intramolecular condensation products. However, if the chain of the diamine was too long and rigid, oligomers or polymers were obtained from the mixture of the macromolecule and the diamine. All results demonstrated that inclusion compounds involving conformationally suitable aromatic diamines were thermodynamically favorable candidates in the mixture due to the restriction of the macrocycle size. Furthermore, kinetic and thermodynamic studies of self-sorting behaviors of both mixed 4O-5O and 4O-6O systems were investigated in detail. Finally, theoretical calculations were also employed to further understand such self-sorting behavior, and indicated that the large enthalpy change of H(2)NArArNH(2)@4O is the driving force for the sorting behavior. Our system may provide a model to further understand the principle of biomolecules with high specificity due only to their conformational self-adjusting ability.     

Modular Synthesis of Novel Macrocycles Bearing α,β‐Unsaturated Chemotypes through a Series of One‐Pot,Sequential Protocols

A series of one‐pot, sequential protocols was developed for the synthesis of novel macrocycles bearing α,β‐unsaturated chemotypes. The method highlights a phosphate tether‐mediated approach to establish asymmetry, and consecutive one‐pot, sequential processes to access the macrocycles with minimal purification procedures. This library amenable strategy provided diverse macrocycles containing α,β‐unsaturated carbon‐, sulfur‐, or phosphorus‐based warheads.     

Perfluoroalkylated 4,13-diaza-18-crown-6 ethers: synthesis, phase-transfer catalysis, and recycling studies

A series of N,N'-dialkyl-4,13-diaza-18-crown-6 lariat ethers possessing two C8H17 (2), (CH2)3C8F17 (3), (CH2)3C10F21 (4), and (CH2)2C8F17 (5) side arms were synthesized in good yields by N-alkylation of 4,13-diaza-18-crown-6. Potassium picrate could be extracted from an aqueous solution into an organic phase by all of the perfluoroalkylated macrocycles demonstrating their potential to be used as phase-transfer catalysts, and preliminary studies on a classical nucleophilic substitution established that they each gave higher catalytic activities under solid-liquid than under liquid-liquid phase-transfer conditions. The light fluorous macrocycles gave similar, if not better, catalytic activity compared to the parent, non-fluorinated phase-transfer catalyst 2 under solid-liquid conditions in conventional organic solvents in both an aliphatic and an aromatic nucleophilic substitution. N,N'-Bis(1H,1H,2H,2H,3H,3H-perfluoroundecyl)-4,13-diaza-18-crown-6 (3) was recycled six times in the iodide displacement reaction of 1-bromooctane and four times in the fluoride displacement reaction of 2,4-dinitrochlorobenzene using fluorous solid-phase extraction without any loss in activity.     

Synthesis, structures and reactivity of macrocyclic imidazolylboranes

New macrocyclic imidazolylboranes [imidazolylB(R¹)₂]_n, where selected carbon atoms of imidazolyl rings may bear substituents other than hydrogen, and where n=4 or 5, are obtained from 1-trimethysilylimidazoles and haloboranes XB(R¹)₂ by boron/silicon exchange using 2-bromoimidazole and benzimidazole. These macrocycles are formally zwitterionic and contain imidazolyl rings linked through their nitrogen atoms by BH₂, B(R¹)₂ or BR¹X units. Despite the sterical demand of these derivatives tetrameric macrocycles are formed. A new synthetic strategy to macrocyclic imidazolylboranes includes the preparation and cyclization of bis(imidazolyl)boronium chlorides. In addition dihaloboranes have been tested for cyclization to yield halogen-containing macrocycles. The new compounds are spectroscopically characterized and X-ray structure analyses of tetrameric- (2a) and pentameric 1-imidazolylborane (2a′), tetrameric 1-imidazolyldimethylborane (2b), tetrameric 1-(2-bromo)imidazolylborane (2d) and bis(2-bromoimidazolyl)boronium chloride (3d) are reported.     

Photochemistry and Photophysical Properties of Novel, Unsymmetrically Substituted Metallophthalocyanines

Abstract— A series of novel, unsymmetrically substituted metallophthalocyanines was synthesized, along with their symmetrically substituted analogs, and the effects of structure and metal substitution on their photophysical and photoredox properties were investigated. The macrocy-cles were synthesized using a mixed-condensation method followed by chromatographic separation of the resulting soluble products. They possess a catechol "active site" and three tert-butyl groups for enhanced solubility. The ground- and excited-state photophysical properties of the free-base, Zn(II) and Pd(II) macrocycles were measured and compared with their symmetrically substituted (tetra[ tert -butyl]) analogs. The efficiency with which these macrocycles sensitize the formation of singlet oxygen was determined and discussed in the context of the excited-state photophysical properties. Several examples of photoinduced electron transfer reactions with one- and two-electron acceptors are demonstrated and discussed. These soluble molecules can be tuned to optimize their photochemical and redox properties by varying the central metal, axial ligands and other substituents, thereby providing a series of molecules for the investigation of photodynamic therapy and photoinduced electron transfer mechanisms.     

Hydrogen-bonded aryl amide macrocycles: synthesis, single-crystal structures, and stacking interactions with fullerenes and coronene

Six hydrogen-bonded shape-persistent aryl amide macrocycles have been prepared by using one-step and (for some) step-by-step approaches. From the one-step reactions, 3 + 3, 2 + 2, or even 1 + 1 macrocycles were obtained in modest to good yields. The reaction selectivity was highly dependent on the structures of the precursors. The X-ray structural analysis of two methoxyl-bearing macrocycles revealed intramolecular hydrogen bonding and weak intermolecular stacking interaction; no column-styled stacking structures were observed. The 1H (DOSY) NMR, UV-vis, and fluorescent experiments indicated that the new rigidified macrocycles complex fullerenes or coronene in chloroform through intermolecular pi-stacking interaction. The association constants of the corresponding 1:1 complexes have been determined if the stacking was able to cause important fluorescent quenching of the macrocycles or coronene.