Sterically Crowded Trianglimines—Synthesis,Structure, Solid‐State Self‐Assembly,and Unexpected Chiroptical Properties

The chiral, triangular‐shape hexaimine macrocycles (trianglimines), bearing bulky alkynyl or aryl substituents were synthesized and studied by means of experimental and theoretical methods. The macrocyclization reactions are driven by the extraordinary stability of the trianglimine ring and provided products with high yields. Electrostatic repulsion between imine nitrogen atoms and the substituents forced an anti conformation of the aromatic linkers. Although the DFT‐optimized structure of 7 is D₃ symmetrical, in the crystal, the macrocycle adopts a bowl‐like molecular shape. The macrocycle self‐assembles into tail‐to‐tail dimers by mutual interdigitation of aromatic moieties. In contrast, macrocycle 8 adopts a rigid pillararene‐like conformation. The nature of the substituent significantly affects the electronic properties of the linker. As a result, unexpectedly high exciton Cotton effects are observed in the electronic circular dichroism (ECD) spectra. The origin of these effects was subject of an in‐depth study.     

Asymmetric,regio‐ and stereo‐selective alternating copolymerization of CO2 and propylene oxide catalyzed by chiral chromium Salan complexes

Chiral chromium complexes of tetradentate N,N′‐disubstituted bis(aminophenoxide) (designated as Salan, a saturated version of Schiff‐base Salen ligand) in conjunction with an ionic quaternary ammonium salt can efficiently catalyze the copolymerization of CO₂ with racemic propylene oxide (rac‐PO) at mild conditions to selectively afford completely alternating poly(propylene carbonate) (PPC) with ～ 95% head‐to‐tail linkages and moderate enantioselectivity. These new catalyst systems predominantly exceed the previously much‐studied SalenCr(III) systems in catalytic activity, polymer enantioselectivity, and stereochemistry control. The chiral diamine backbone, sterically hindered substitute groups on the aromatic rings, and the presence of sp³‐hydridized amino donors and its N,N′‐disubstituted groups in chiral SalanCr(III) complexes all play significant roles in controlling polymer stereochemistry and enantioselectivity. Furthermore, a relationship between polycarbonate enantioselectivity and its head‐to‐tail linkages in relation to regioselective ring‐opening of the epoxide was also discussed on the basis of stereochemical studies of PPCs derived from the copolymerization of CO₂ with chiral PO at various conditions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6102–6113, 2008     

Comprehensive structural characterization of polyisoprene synthesized via cationic mechanism

The microstructure of polyisoprene synthesized with ^tBuCl/TiCl₄ initiating system is investigated using 1D and 2D (HSQC and HMBC) NMR spectroscopy. It is found that trans‐1,4‐units with regular (head‐to‐tail) and inverse (tail‐to‐tail) and (head‐to‐head) enchainments are predominant structures of unsaturated part of polymer chain, while 1,2‐ and 3,4‐units are presented in minor amounts. The new methodology for the quantitative calculation of the content of different structural units in polyisoprene chain including both types of inverse trans‐1,4‐addition (tail‐to‐tail and head‐to‐head) is proposed. It is shown that head groups consist of tert‐butyl group connected to trans‐1,4‐unit of polyisoprene chain. In addition, two types of chlorine‐containing end groups are found (trans‐4,1‐Cl and 4,3‐Cl), while conjugated double bonds at the chain end are totally absent. The methodology for the calculation of number‐average functionality by tert‐butyl head and chlorine end groups, respectively, is developed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2430–2442     

Formation of Metal‐Assisted Stable Double Helices in Dimers of Cyclic Bis‐Tetrapyrroles that Exhibit Spring‐Like Motion

Bidipyrrin‐bridged macrocycles, prepared from Ni^II‐bridged dipyrrin‐based nanorings by intramolecular oxidative biaryl coupling reactions, yielded [2+4]‐type Zn^II‐assisted stable twisted‐ring dimers comprising two double helices. These [2+4]‐type metal complexes can be optically resolved by chiral HPLC and exhibit tunable electronic and optical properties as a result of spring‐like motions. The double helices behave as glue to connect two macrocycles and as the screws of hinges to form thermally responsive synchronized spring systems.     

Exploring Crystal Structure in Ethyne‐Substituted Pentacenes,and Their Elaboration into Crystalline Dehydro[18]annulenes

Approaches to control the self‐assembly of aromatic structures to enhance intermolecular electronic coupling are the key to the development of new electronic and photonic materials. Acenes in particular have proven simple to functionalize to induce strong π‐stacking interactions, although finer control of intermolecular π‐overlap has proven more difficult to accomplish. In this report, we describe how very weak hydrogen bonding interactions can exert profound impact on solid‐state order in solubilized pentacenes, inducing self‐assembly in either head‐to‐tail motifs with strong 2‐D π‐stacking, or head‐to‐head orientations with much weaker, 1‐D π‐stacking arrangements. In order to achieve 3‐D π‐stacking useful for photovoltaic applications, we elaborated a series of diethynyl pentacenes to their trimeric dehydro[18]annulene forms. These large, strongly interacting structures did indeed behave as acceptors in polymer photovoltaic devices.     

Modification of D‐glucose‐based 18‐crown‐6 ethers by phosphorylation and phosphinylation

The primary hydroxy groups of head‐tail and head‐head bis(sugar)‐based crown ethers ( 1 and 3 , respectively) were acylated by (EtO)₂P(O)Cl and Ph₂P(O)Cl in a selective manner. Cation binding ability of the bis‐phosphorylated and phosphinylated macrocycles ( 2 and 4 ) was evaluated by the picrate extraction method. Introduction of the P‐moieties led to increase of the extraction ability without significant selectivity. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:267–270, 2000     

Macrocycle Embrace: Encapsulation of Fluoroarenes by m‐Phenylene Ethynylene Host

We report structural characterization of a new member of m‐phenylene ethynylene ring family. This shape‐persistent macrocycle also co‐crystallizes with hexafluoro‐, 1,2,4,5‐tetrafluoro‐, 1,3,5‐trifluoro, and 1,4‐difluorobenzene. The four complexes are almost isostructural, and all show the fluoroarene included into the central cavity of the macrocycle. Characterized by multiple short C?H???F?C contacts, these inclusion complexes further dimerize in the solid state into a 2+2 assembly, in which the two macrocycles embrace each other by their large hydrophobic groups that are rotated by 60° relative to one another.     

Optimal Configurations of “Capped” β‐Cyclodextrin Dimers in Water Maximise Hydrophobic Association

Circular dichroism analysis and proton NMR experiments revealed that solutions of 3‐O‐(2‐methylnaphthyl)‐β‐cyclodextrin form different dimer configurations. The exact nature of the dimer configurations were postulated to be of three types in which these capped cyclodextrins (CDs) are orientated in head‐to‐head and head‐to‐tail arrangements. Here we show from detailed computer simulations and free‐energy calculations on the configurations that the head‐to‐head configuration in which the naphthyl groups are mutually inserted into each other’s CD cavities is the most favoured configuration. This configuration optimises the hydrophobic association of the naphthyl aromatic groups and the ring cavities as well as forming the most inter‐CD hydrogen bonds of the three configurations.     

The structural and dynamic properties of 1‐bromodecane in urea inclusion compounds investigated by solid‐state 1H, 13C and 2H NMR spectroscopy

For asymmetric guest molecules in urea, the end‐groups of two adjacent guest molecules may arrange in three different ways: head–head, head–tail and tail–tail. Solid‐state ¹H and ¹³C NMR spectroscopy is used to study the structural properties of 1‐bromodecane in urea. It is found that the end groups of the guest molecules are randomly arranged. The dynamic characteristics of 1‐bromodecane in urea inclusion compounds are probed by variable‐temperature solid‐state ²H NMR spectroscopy (line shapes, spin–spin relaxation: T₂, spin‐lattice relaxation: T_1Z and T_1Q) between 120 K and room temperature. The comparison between the simulation and experimental data shows that the dynamic properties of the guest molecules can be described in a quantitative way using a non‐degenerate three‐site jump process in the low‐temperature phase and a degenerate three‐site jump in the high‐temperature phase, in combination with the small‐angle wobbling motion. The kinetic parameters can be derived from the simulation. Copyright © 2011 John Wiley & Sons, Ltd.     

Triply Linked Corrole Dimers

The oxidation of 10–10′ singly linked corrole dimers with DDQ at low concentration in CHCl₃ afforded meso–meso, β–β, β–β triply linked 2H‐corrole dimers (with two inner NH groups in each corrole unit), which exhibited characteristic ¹H NMR and absorption spectra attributable to their nonaromatic electronic networks. These 2H‐corrole dimers were reduced with NaBH₄ to aromatic 3H‐corrole dimers, which were unstable and easily oxidized back to the 2H‐corrole dimers upon exposure to air. Bis(zinc(II)) complexes of the 2H‐corrole dimers were synthesized and characterized as rare examples of nonaromatic zinc(II) corrole complexes.     

Triply Linked Corrole Dimers

The oxidation of 10–10′ singly linked corrole dimers with DDQ at low concentration in CHCl₃ afforded meso–meso, β–β, β–β triply linked 2H‐corrole dimers (with two inner NH groups in each corrole unit), which exhibited characteristic ¹H NMR and absorption spectra attributable to their nonaromatic electronic networks. These 2H‐corrole dimers were reduced with NaBH₄ to aromatic 3H‐corrole dimers, which were unstable and easily oxidized back to the 2H‐corrole dimers upon exposure to air. Bis(zinc(II)) complexes of the 2H‐corrole dimers were synthesized and characterized as rare examples of nonaromatic zinc(II) corrole complexes.     

Solid‐State [2+2] Photodimerization of 1‐Aryl‐4‐pyridylbutadienes in Cation‐π‐Controlled Crystals

Irradiation of HX (X=CF₃SO₃ or CF₃CO₂) salts of 1‐aryl‐4‐pyridylbutadienes 1 a – 1 c in the solid‐state afforded syn head‐to‐tail dimers in good yields among a number of possible dimers, whereas irradiation of the neutral substrates gave a complex mixture or no products. A comparison of the X‐ray crystal structures of the neutral compounds and the HX salts clarified that their orientation modes are head‐to‐head and head‐to‐tail, respectively. Moreover, while the distances between the two neighboring double bonds of the neutral compounds are relatively far apart from each other, those of HX salts are close together, satisfying Schmidt's requirement. These findings suggested that cation‐π interactions between the pyridinium and aromatic rings are effective for the preorientation of the HX salts of substrates, leading to photodimers in high regio‐ and stereoselectivities.     

Organotin adducts with pyrimidinethione: crystal structure of dimethyldi(pyrimidine‐2‐thiolato)tin(IV) and diphenyldi(pyrimidine‐2‐thiolato)tin(IV)

The complexes dimethyldi(pyrimidine‐2‐thiolato)tin(IV) ( 1 ) and diphenyldi(pyrimidine‐2‐thiolato)tin(IV) ( 2 ) have been structurally ­characterized by means of X‐ray crystallography. Complex 1 exhibits strong π–π stacking interactions and adduct 2 is self‐assembled via intermolecular hydrogen bonds, C H–π and π–π stacking interactions. Partial solvolysis occurs in organic solvents for 1 and 2 . Copyright © 2000 John Wiley & Sons, Ltd.     

One‐dimensional uranium–organic framework in catena‐poly[[di‐μ2‐hydroxido‐bis[dioxouranium(VI)]]‐di‐μ2‐2‐pyridylacetato‐κ3O,N:O′;κ3O:O′,N]

In the title compound, {[UO₂(C₇H₆NO₂)(OH)]}_n, the U atom is in a seven‐coordinated pentagonal–bipyramidal environment. Each uranyl ion is bound to the N and one of the O atoms of a 2‐pyridylacetate ligand, to one O atom from a second ligand and to two bridging hydroxide groups, all located in the equatorial plane. Hydroxide bridging gives uranyl dimers, which are assembled into planar and rectilinear ribbons by carboxylate bridges. 12‐Membered rings are defined by proximal dimers in the ribbons, with two intra‐ring hydrogen bonds involving the hydroxide groups and two carboxylate O atoms.     

Synthesis,Electrochemistry, and Photophysical Studies of Ruthenium(II) Polypyridine Complexes with D–π–A–π–D Type Ligands and Their Application Studies as Organic Memories

A new class of ruthenium(II) polypyridine complexes with a series of D–π–A–π–D type (D=donor, A=acceptor) ligands was synthesized and characterized by ¹H NMR spectroscopy, mass spectrometry, and elemental analysis. The photophysical and electrochemical properties of the complexes were also investigated. The newly synthesized ruthenium(II) polypyridine complexes were found to exhibit two intense absorption bands at both high‐energy (λ=333–369 nm) and low‐energy (λ=520–535 nm) regions. They are assigned as intraligand (IL) π→π* transitions of the bipyridine (bpy) and π‐conjugated bpy ligands, and IL charge‐transfer (CT) transitions from the donor to the acceptor moiety with mixing of dπ(Ru^II)→π*(bpy) and dπ(Ru^II)→π*(L) MLCT characters, respectively. In addition, all complexes were demonstrated to exhibit intense red emissions at approximately λ=727–744 nm in degassed dichloromethane at 298 K or in n‐butyronitrile glass at 77 K. Nanosecond transient absorption (TA) spectroscopy has also been carried out, establishing the presence of the charge‐separated state. In order to understand the electrochemical properties of the complexes, cyclic voltammetry has also been performed. Two quasi‐reversible oxidation couples and three quasi‐reversible reduction couples were observed. One of the ruthenium(II) complexes has been utilized in the fabrication of memory devices, in which an ON/OFF current ratio of over 10⁴ was obtained.     

Formation of regioregular head‐to‐tail poly[3‐(4‐butylphenyl)thiophene] by an oxidative coupling polymerization with vanadium acetylacetonate

The mechanism for the formation of head‐to‐tail (H–T) poly[3‐(4‐butylphenyl)thiophene] by oxidative coupling polymerization with a catalytic amount of vanadium acetylacetonate was investigated. Polymerization was carried out in the presence of vanadium acetylacetonate, trifluoromethane sulfonic acid, and trifluoroacetic anhydride under an oxygen atmosphere in 1,2‐dichloroethane at room temperature. Polymers and oligomers obtained after several polymerization times were characterized by gel permeation chromatography, IR, and NMR spectroscopies. With these findings and the reactivity of monomer and dimers based on ab initio density functional theory, the polymerization was found to proceed mainly through the formation of H–T linkages due to the high spin density at the 2‐position of 3‐(4‐butylphenyl)thiophene and the calculated total energy of dimers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2287–2295, 2001     

Head‐to‐head dimers in the zwitterion of 1‐hydroxy‐1‐phosphono‐3‐(1‐piperidino)propylidene‐1‐phosphonate (PHPBP)

The title compound, C₈H₁₉NO₇P₂, is a member of the bis­phosphonate family of therapeutic compounds. PHPBP has inner‐salt character, consisting of a negatively charged PO₃ group and a positively charged N atom. The six‐membered piperidine ring adopts an almost‐perfect chair conformation. The hydroxyl group and the N atom have gauche and trans conformations in relation to the O—C—C—C—N backbone, respectively. Hydrogen bonding is the main contributor to the packing in the crystal, which consists of head‐to‐head dimers formed through phosphonyl–phosphonyl hydrogen bonds, while O—H⋯O and N—H⋯O interactions join the dimers into a plane parallel to crystallographic b and c axes.     

Hydrogen‐bonding features in the 1:2 adduct of 4‐aminobenzoic acid and l‐proline

The title adduct, 4‐aminobenzoic acid–l ‐proline–water (1/2/1), C₇H₇NO₂·2C₅H₉NO₂·H₂O, contains two independent proline chains with a C(5) motif, each of the head‐to‐tail type and each held together by N—H...O hydrogen bonds, propagated parallel to the b and c axes of the unit cell. Thus, the proline residues aggregate parallel to the ac plane. 4‐Aminobenzoic acid (PABA) residues are arranged on both sides of the proline aggregate and are connected through water O atoms, which act as acceptors for PABA and as hydrogen‐bond donors to the amino acids. The characteristic features of PABA, viz. twisting of the carboxyl plane from the aromatic ring and the formation of a head‐to‐tail chain motif [C(8)] along the b axis, are observed. A distinct feature of the structure is that no proton transfer occurs between proline and PABA.     

Computational Study of the Interactions between Benzene and Crystalline Ice Ih: Ground and Excited States

Ground‐state geometries of benzene on crystalline ice cluster model surfaces (I_h) are investigated. It is found that the binding energies of benzene‐bound ice complexes are sensitive to the dangling features of the binding sites. We used time‐dependent DFT to study the UV spectroscopy of benzene, ice clusters, and benzene–ice complexes, by employing the M06‐2X functional. It is observed that the size of the ice cluster and the dangling features have minor effects on the UV spectral characteristics. Benzene‐mediated electronic excitations of water towards longer wavelengths (above 170 nm) are noted in benzene‐bound ice clusters, where the cross‐section of photon absorption by water is negligible, in good agreement with recent experimental results (Thrower et al., J. Vac. Sci. Technol. A, 2008, 26 , 919–924). The intensities of peaks associated with water excitations in benzene–ice complexes are found to be higher than in isolated ice clusters. The π→π* electronic transition of benzene in benzene–ice complexes undergoes a small redshift compared with the isolated benzene molecule, and this holds for all benzene‐bound ice complexes.     

Two‐Step Synthesis of Complex Artificial Macrocyclic Compounds

The design and synthesis of head‐to‐tail linked artificial macrocycles using the Ugi‐reaction has been developed. This synthetic approach of just two steps is unprecedented, short, efficient and works over a wide range of medium (8–11) and macrocyclic (≥12) loop sizes. The substrate scope and functional group tolerance is exceptional. Using this approach, we have synthesized 39 novel macrocycles by two or even one single synthetic operation. The properties of our macrocycles are discussed with respect to their potential to bind to biological targets that are not druggable by conventional, drug‐like compounds. As an application of these artificial macrocycles we highlight potent p53–MDM2 antagonism.