Metal-free double azide addition to strained alkynes of an octadehydrodibenzo[12]annulene derivative with electron-withdrawing substituents.

Strain-promoted azide-alkyne cycloaddition (SpAAC) is a powerful tool in the field of bioconjugation and materials research. We previously reported a regioselective double addition of organic azides to octadehydrodibenzo[12]annulene derivatives with electron-rich alkyloxy substituents. In order to increase the reaction rate, electron-withdrawing substituents were introduced into octadehydrodibenzo[12]annulene.

Efficient Transformation of Polymer Main Chain Catalyzed by Macrocycle Metal Complexes via Pseudorotaxane Intermediate.

Post-synthesis modification of polymers streamlines the synthesis of functionalized polymers, but is often incomplete due to the negative polymer effects. Developing efficient polymer reactions in artificial systems thus represents a long-standing objective in the fields of polymer and material science. Here, we show unprecedented macrocycle-metal-complex-catalyzed systems for efficient polymer reaction that result in 100 % transformation of the main chain functional groups presumably via a processive mode reaction.

Acid Dissociation Constants of the Benzimidazole Unit in the Polybenzimidazole Chain: Configuration Effects.

The acid dissociation constant of three benzimidazoles, namely 2,2'-bibenzo[d]imidazole, 2,5'-bibenzo[d]imidazole, and 5,5'-bibenzo[d]imidazole, have been investigated by means of density functional theory calculations in gas phase and in aqueous solution. The theoretical approach was validated by the comparing of predicted and experimentally determined p values in imidazole, benzimidazole, and 2-phenylbenzimidazole. From the studied compounds, 2,2'-bibenzo[d]imidazole was found to be the most acidic, which made it a valuable candidate as a material for polymer electrolyte membrane fuel cells.

Acceleration of Liquid-Crystalline Phase Transition Simulations Using Selectively Scaled and Returned Molecular Dynamics.

The molecular dynamics (MD) technique to accelerate simulation of phase transition to liquid-crystalline (LC) phases is demonstrated on the model LC system 4-octyl-4'-cyanobiphenyl (8CB) smectic A phase. Simulation of a phase transition to a smectic phase is challenging because an intrinsically long simulation time and large system size are required owing to the high order and low onset temperature. Acceleration of the simulated transition of 8CB to the smectic A phase was ultimately achieved by selectively weakening the intermolecular Lennard-Jones interaction of alkyl chains and then returning the scaled interaction to the unscaled one.

N-Methylated Peptide Synthesis via Generation of an Acyl N-Methylimidazolium Cation Accelerated by a Brønsted Acid.

The development of a robust amide-bond formation remains a critical aspect of N-methylated peptide synthesis. In this study, we synthesized a variety of dipeptides in high yields, without severe racemization, from equivalent amounts of amino acids. Highly reactive N-methylimidazolium cation species were generated in situ to accelerate the amidation.

Open clamshell dinuclear palladium(ii) complexes possessing out-of-plane anisotropy.

Double cyclometalation of planar, oligomeric phenylpyridines yielded dinuclear palladium(ii) complexes with novel out-of-plane anisotropy. An X-ray crystal structure analysis revealed that the complexes exhibit concave-convex geometry, and 1H NMR measurement evidenced the occurrence of stable out-of-plane anisotropy. The dipole moment and Pd-Pd interaction were investigated by theoretical calculations.

Rhodium-Catalyzed Annulative Coupling of Isothiazoles with Alkynes through N-S Bond Cleavage.

A Rh(III)-catalyzed annulative coupling of 3,5-diarylisothiazoles and alkynes is reported. The N-S bond in the isothiazole ring acts as an internal oxidant to regenerate the Rh(III) species in combination with an external Cu(II) oxidant, and the corresponding 1:2 coupling products are obtained. The remarkable difference in the reaction outcome between isothiazoles and the relevant isoxazoles has been investigated by DFT calculations, revealing that the relative stability of the enolate intermediates dictates the product selectivity.

Atomistic Mechanism of Anisotropic Heat Conduction in the Liquid Crystal 4-Heptyl-4'-cyanobiphenyl: All-Atom Molecular Dynamics.

All-atom molecular dynamics simulations were performed on 4-heptyl-4'-cyanobiphenyl (7CB) to study the mechanism of heat conduction in this nematic liquid crystal atomistically. To describe 7CB properly, the AMBER-type force field was optimized for the dihedral parameter of biphenyl and the Lennard-Jones parameters. The molecular dynamics calculation using the optimized force field well reproduced the experimental values of the isotropic-nematic phase transition temperature, density, and anisotropy of the thermal conductivity.

Triptycenyl Sulfide: A Practical and Active Catalyst for Electrophilic Aromatic Halogenation Using -Halosuccinimides.

A Lewis base catalyst Trip-SMe (Trip = triptycenyl) for electrophilic aromatic halogenation using -halosuccinimides (NXS) is introduced. In the presence of an appropriate activator (as a noncoordinating-anion source), a series of unactivated aromatic compounds were halogenated at ambient temperature using NXS. This catalytic system was applicable to transformations that are currently unachievable except for the use of Br or Cl: e.

Diels-Alder reactions of 1-phosphabutadienes: a highly selective route to P[double bond, length as m-dash]C-substituted phosphacyclohexenes.

Kinetically stabilized 1-phosphahaloprenes (2-halo-1-phosphabutadienes) as well as 1-phosphaisoprene undergo a hitherto unknown phospha-Diels-Alder dimerization of the P[double bond, length as m-dash]C-C[double bond, length as m-dash]C units upon heating. The [4+2] cyclodimerization is highly stereo- and regio-selective. The phosphaalkene-substituted phosphacyclohexene product is an unprecedented P(sp),P(sp) ligand that is of interest in polymer/materials science and catalysis.

Macrocyclic Metal Complexes Bearing Rigid Polyaromatic Ligands: Synthesis and Catalytic Activity.

We synthesised palladium and platinum complexes possessing cyclic and acyclic pincer-type polyaromatic ligands and investigated their structural effect on the catalysis. The pincer-type bis(6-arylpyridin-2-yl)benzene skeleton was constructed via Kröhnke pyridine synthesis under transition metal-free conditions on gram-scale quantity. Ligand structure significantly influenced catalytic activity toward the platinum-catalysed hydrosilylation of diphenyl acetylenes, despite the ligand-independence of the conformations and electronic properties of these complexes.

Design, synthesis, and evaluation of azo D-π-A dyes as photothermal agents.

Thirteen readily accessible azo D-π-A dyes, intended for use as photothermal agents, were synthesized using only a few steps. Absorption wavelengths were readily tuned by changing the building blocks, and 6 of these dyes exhibited NIR absorption that would be useful for biomedical applications. Unexpected suppression of an N-C single bond rotation that neighbors the azo bond was observed in the case of 5 dyes.

Cationic Chiral Pd-Catalyzed "Acetylenic" Diels-Alder Reaction: Computational Analysis of Reversal in Enantioselectivity.

The highly enantioselective Diels-Alder reaction of acetylenic dienophiles is shown to be effectively catalyzed by cationic chiral palladium complexes. Not only the degree but also the sense of enantioselectivity critically depends on the steric demand of ligands. Computational analyses indicate that the steric demand does not affect the endo/exo-selectivity but the enantioface selectivity of dienes.

Diphosphination of Arynes with Diphosphines.

A diphosphination of arynes with diphosphines has been developed. The reaction of stable aryne precursors, 2-(trimethylsilyl)aryl triflates, with tetraaryldiphosphines proceeds in the presence of fluorine- or carbonate-based activators to deliver the corresponding diphosphinated products, sterically and electronically tuned 1,2-bis(diphenylphosphino)benzene (dppbz) derivatives, which can find wide application in transition metal catalysis and material science. Additionally, preliminary computational studies on the reaction mechanism are also reported.

Rhodium(III)-Catalyzed Oxidative Coupling of N-Phenylindole-3-carboxylic Acids with Alkenes and Alkynes via C4-H and C2-H/C2'-H Bond Cleavage.

The rhodium(III)-catalyzed direct alkenylation of N-phenylindole-3-carboxylic acids with alkenes including acrylate ester, acrylamide, and acrylonitrile proceeds smoothly at the C4-position through regioselective C-H bond cleavage directed by the carboxyl group. In marked contrast, the indole substrates react with diarylacetylenes accompanied by cleavage of the C2-H and C2'-H bonds and decarboxylation to produce 5,6-diarylindolo[1,2- a]quinolone derivatives. DFT calculations have suggested that the smooth insertion of an alkene to a C4-rhodated six-membered metallacycle intermediate leads to the C4 alkenylated products, while the latter annulation at the C2- and C2'-positions is attributable to facile reductive elimination in the corresponding seven-membered metallacycles formed by the double C-H bond cleavage and alkyne insertion.

Iridium-Catalyzed Aerobic Coupling of Salicylaldehydes with Alkynes: A Remarkable Switch of Oxacyclic Product.

The iridium(III)/copper(II)-catalyzed dehydrogenative coupling of salicylaldehydes with internal alkynes proceeds efficiently under atmospheric oxygen through aldehyde C-H bond cleavage and decarbonylation. A variety of benzofuran derivatives can be synthesized by the environmentally benign procedure. DFT calculations suggest that this unique transformation involves the facile deinsertion of CO in the key metallacycle intermediate, which is in marked contrast to the corresponding rhodium(III) catalysis that leads to CO-retentive chromone derivatives.

Formal Lossen Rearrangement/[3+2] Annulation Cascade Catalyzed by a Modified Cyclopentadienyl Rh Complex.

It has been established that a cyclopentadienyl Rh complex with two phenyl groups and a pendant amide moiety catalyzes the formal Lossen rearrangement/[3+2] annulation cascade of N-pivaloyl benzamides and acrylamides with alkynes leading to substituted indoles and pyrroles. Mechanistic studies revealed that this cascade reaction proceeds via not the Lossen rearrangement to form anilides or enamides but C-H bond cleavage, alkyne insertion, and the formal Lossen rearrangement.

Rhodium-Catalyzed Cascade Synthesis of Benzofuranylmethylidene-Benzoxasiloles: Elucidating Reaction Mechanism and Efficient Solid-State Fluorescence.

A new synthetic route to highly fluorescent benzofuranylmethylidenebenzoxasiloles through cationic rhodium(I)/binap complex-catalyzed cascade cycloisomerization of bis(2-ethynylphenol)silanes has been developed involving 1,2-silicon and 1,3-carbon (alkyne) migrations followed by oxycyclization. The present synthesis requires only three steps, starting from commercially available dichlorodiisopropylsilane, which is markedly shorter than our previous synthesis (eight steps starting from commercially available chlorodiisopropylsilane). Theoretical calculations elucidated the mechanism of the above cascade cycloisomerization.

Synthesis, Structures, and Photophysical Properties of Alternating Donor-Acceptor Cycloparaphenylenes.

The synthesis of alternating donor-acceptor [12] and [16]cycloparaphenylenes (CPPs) has been achieved by the rhodium-catalyzed intermolecular cross-cyclotrimerization followed by imidation and/or aromatization. These alternating donor-acceptor CPPs showed positive solvatofluorochromic properties and smaller HOMO-LUMO gaps compared with nonfunctionalized CPPs, which was confirmed by the theoretical study.

Synthesis of Alkynylmethylidene-benzoxasiloles through a Rhodium-Catalyzed Cycloisomerization Involving 1,2-Silicon and 1,3-Carbon Migration.

It is shown that a cationic rhodium(I)/biphep complex catalyzes the cycloisomerization of 2-(alkynylsilylethynyl)phenols, leading to alkynylmethylidene-benzoxasiloles through concomitant silicon and carbon migration. This unprecedented cycloisomerization presumably proceeds via the formation of rhodium vinylidenes through 1,2-silicon migration, followed by 1,3-carbon (alkyne) migration via the formation of hypervalent silicon centers.

Rh-Mediated Enantioselective Synthesis, Crystal Structures, and Photophysical/Chiroptical Properties of Phenanthrenol-Based [9]Helicene-like Molecules.

The enantioselective synthesis of phenanthrenol-based [9]helicene-like molecules has been achieved via the rhodium-mediated intramolecular [2 + 2 + 2] cycloadditions of 3-phenanthrenol-linked triynes. Crystal structures and photophysical/chiroptical properties of these [9]helicene-like molecules were compared with the corresponding [7]helicene-like molecules.

Polar Order and Symmetry Breaking at the Boundary between Bent-Core and Rodlike Molecular Forms: When 4-Cyanoresorcinol Meets the Carbosilane End Group.

Two isomeric achiral bent-core liquid crystals involving a 4-cyanoresorcinol core and containing a carbosilane unit as nanosegregating segment were synthesized and were shown to form ferroelectric liquid-crystalline phases. Inversion of the direction of one of the COO groups in these molecules leads to a distinct distribution of the electrostatic potential along the surface of the molecule and to a strong change of the molecular dipole moments. Thus, a distinct degree of segregation of the carbosilane units and consequent modification of the phase structure and coherence length of polar order result.

Structural Analysis and Inclusion Mechanism of Native and Permethylated α-Cyclodextrin-Based Rotaxanes Containing Alkylene Axles.

Native α-cyclodextrin- (α-CD) and permethylated α-CD (PMeCD)-based rotaxanes with various short alkylene chains as axles can be synthesized through a urea end-capping method. Native α-CD tends to form [3]- or [5]pseudorotaxanes and not [2]- or [4]pseudorotaxanes, which indicates that the coupled CDs act as a single fragment. End-capping reactions of the pseudorotaxanes with C18 and C24 axle lengths do not occur because the axle termini are covered by the densely stacked CDs.