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In this study, the impact of one or two hydroxy moieties at the benzo[7]annulene scaffold on the GluN2B affinity and cytoprotective activity was analyzed. The key intermediate for the synthesis of OH-substituted benzo[7]annulenamines 11–13 and 17 was the epoxyketone 8. Reductive epoxide opening of 8 resulted with high regioselectivity in the 5-hydroxyketone 9 (Pd(OAc)2, HCO2H, phosphane ligand) or the 6-hydroxyketone 10 (H2, Pd/C), whereas hydrolysis in aqueous dioxane led to the dihydroxyketone 14. Reductive amination of these ketones with primary amines and NaBH(OAc)3 afforded the benzo[7]annulenamines 11–13 and 17. In receptor binding studies 5-OH derivatives 11 and 12 showed higher GluN2B affinity than 6-OH derivatives 13, which in turn were more active than 5,6-di-OH derivative 17a. The same order was found for the cytoprotective activity of the ligands. The tertiary amine 12a with one OH moiety in 5-position represents the most promising GluN2B negative allosteric modulator with a binding affinity of Ki = 49 nM and a cytoprotective activity of IC50 = 580 nM. In the binding pocket 12a shows a crucial H-bond between the benzylic OH moiety and the backbone carbonyl O-atom of Ser132 (GluN1b). It was concluded that a 5-OH moiety is essential for the inhibition of the NMDA receptor associated ion channel, whereas a OH moiety in 6-position is detrimental for binding and inhibition. An OH or CH2OH moiety at 2-position results in binding at the ifenprodil binding site, but very weak ion channel inhibition.

The 4-benzylpiperidine moiety is a central structural element of potent N-methyl-d-aspartate (NMDA) receptor antagonists containing the GluN2B subunit. To obtain novel GluN2B ligands suitable for positron emission tomography, the benzylpiperidine moiety was replaced with fluorinated ω-phenylalkylamino groups. For this purpose three primary propyl- and butylamines 7 a-c and one butyraldehyde 7 d bearing a fluorine atom and an ω-phenyl moiety were prepared in 3- to 7-step syntheses. Compounds 7 a-d were attached to various scaffolds of potent GluN2B antagonists (scaffold hopping) instead of the original 4-benzylpiperidine moiety. Although benzoxazol-2-ones and indoles with a benzylpiperidine moiety show high GluN2B affinity, the corresponding fluorophenylalkylamine derivatives did not result in high Glu2B affinity. Moderate GluN2B affinity was observed for a 3-(fluoroalkyl)-substituted tetrahydro-1H-3-benzazepine (Ki =239 nm). However, high GluN2B affinity was obtained for the tetrahydro-5H-benzo[7]annulen-7-amines 12 a-c (Ki =17-30 nm). Docking studies resulted in the same binding pose for 12 a as for the lead compound Ro 25-6981. It can be concluded that some GluN2B ligands (benzoxazolones, indoles) do not tolerate replacement of the 4-benzylpiperidine moiety with flexible fluorinated phenylalkyl side chains, but other scaffolds such as tetrahydro-3-benzazepines and -benzo[7]annulenes retain interaction with NMDA receptors containing the GluN2B subunit.

Two environmentally benign methods for the synthesis of quinazolines via acceptorless dehydrogenative coupling of 2-aminobenzylamine with benzyl alcohol (Path A) and 2-aminobenzylalcohol with benzonitrile (Path B), catalyzed by cheap, earth abundant and easy to prepare nickel catalysts, containing tetraaza macrocyclic ligands (tetramethyltetraaza[14]annulene (MeTAA) or 6,15-dimethyl-8,17-diphenyltetraaza[14]annulene (MePhTAA)) are reported. A wide variety of substituted quinazolines were synthesized in moderate to high yields starting from cheap and easily available starting precursors. A few control reactions were performed to understand the mechanism and to establish the acceptorless dehydrogenative nature of the catalytic reactions.

Gentile statistics, which is famous for its advantages in dealing with composite particle systems, is a kind of fractional statistics. Lately, researchers are concentrating on finding real systems that obey Gentile statistics. Five years ago, we discovered that the cyclic hydrocarbon polyenes called N-annulenes in the Hückel model had certain correspondence with Gentile oscillators. According to their rotation and dihedral symmetry, these two systems had the same energy levels and partition functions. In this paper, we give further discussions. We discuss the transformations of wave functions between N-annulenes and Gentile oscillators, the creation and annihilation operators in site pictures of N-annulenes, the coherent state, and the mathematical proofs of the intermediate commutation relations of operators. All of our works prove that N-annulenes in the Hückel model are real Gentile statistical systems and offer a new algebraic method to deal with the problems of electron-electron and electron-phonon interactions.

Reaction of Li2(tmtaa) (tmtaaH2 = dibenzotetramethyltetraaza[14]annulene) with 1 equiv of [UO2Cl2(THF)3], in an attempt to form cis-[UO2(tmtaa)], affords the bis(uranyl) complex [Li(THF)3][Li(THF)2...

A new synthesis of cerium tetrakis(tropolonate), Ce(trop)4, where trop is deprotonated 2-hydroxy-2,4,6-cycloheptatrienone) or Ce(O2C7H5)4, is developed that results in dark-purple crystals whose X-ray crystal structure shows that the geometry of the eight-coordinate compound closely resembles a D2 d dodecahedron, based on shape parameters. The magnetic susceptibility as a function of the temperature (4-300 K) shows that it is a temperature-independent paramagnet, χ = 1.2(3) × 10-4 emu/mol, and the LIII-edge X-ray absorption near-edge structure spectrum shows that the molecule is multiconfigurational, comprised of a f1:f0 configuration mixture in a 50:50 ratio. Ce(acac)4 and Ce(tmtaa)2 (where acac is acetylacetonate and tmtaaH2 is tetramethyldibenzotetraaza[14]annulene) have similar physical properties, as does the solid-state compound CeO2. The concept is advanced that trop-, acac-, tmtaa2-, cot2-, and O2- are redox-active ligands that function as electron donors, rendering the classification of these compounds according to their oxidation numbers misleading because their magnetic susceptibilities, χ, are positive and their effective magnetic moments, μeff, lie in the range of 0.1-0.7 μB at 300 K.

The low-lying triplet state of a recently published compound (TMTQ, Angew. Chem. Int. Ed. 2015, 20, 5888), was analyzed quantum chemically in light of suggestions that it is influenced by Baird-aromaticity. Two mesomeric structures describe this state; a zwitterionic Baird-aromatic structure with a triplet biradical 8pi-electron methano[10]annulene (M10A) dicationic ring, and a Hückel-aromatic with a neutral closed-shell 10pi-electron ring. According to charge and spin density distributions, the Hückel-aromatic structure dominates the triplet state (the Baird-aromatic contributes at most 12%), and separation of the FLU aromaticity index into alpha and beta electron contributions emphasizes this finding. The small singlet-triplet energy gap is due to Hückel-aromaticity of the M10A ring, clarified by comparison to the smaller analogues of TMTQ. Yet, TMTQ and its analogues are Hückel-Baird hybrids allowing for tuning between closed-shell 4n+2 Hückel-aromaticity and open-shell 4n Baird-aromaticity This work has been supported by the Swedish Research Council (project grant 621-2011-4177), Ministerio de Economía y Competitividad (MINECO) of Spain (Project CTQ2014-54306-P) and the Generalitat de Catalunya (project 2014SGR931, Xarxa de Referència en Química Teòrica i Computacional, and ICREA Academia 2014 prize for M.S.). F.F. acknowledges financial support of the Beatriu de Pinós programme from AGAUR for the postdoctoral grants BP_A_00339 and BP_A2_00022. M.S. and F.F. are grateful to the European Union (EU) for FEDER fund number UNGI10-4E-801

Thermally stable bisdehydro[12]- and tetrakisdehydro[16]annulenes with planar structures were successfully synthesized by fusion with two dithieno[3,4- b:3',4'- d]thiophene units. The planarized [4n]annulene cores induced substantial antiaromaticity. However, the HOMO-LUMO gap slightly increased as the π-core expanded from the planar cyclooctatetraene. This phenomenon, in contrast to that of typical π-conjugated systems, was attributed to the decrease in antiaromaticity of the [4n]annulene cores. Both TD-HF and GIAO-HF calculations supported this conclusion.

A detailed mechanistic study of the cyclopropanation of electron-deficient alkenes, namely methyl acrylate with ethyl diazoacetate (EDA), was carried out, aiming at understanding both the superior activity and the higher sensitivity of the cobalt(II) tetramethyldibenzotetraaza[14]annulene [Co(MeTAA)] catalyst as compared with cobalt(II) tetraphenylporphyrin [Co(TPP)]. Cobalt(III)-carbene radicals were demonstrated to be present as key intermediates in the reaction, using a combination of kinetic studies, experimental EPR spin-trapping experiments, and supporting DFT studies. Reaction progress was monitored in real time by observing N 2 formation and measuring its partial pressure under isothermal conditions. Reaction progress kinetic analysis (RPKA) was used to analyze the experimental data. Results showed that the reaction is first-order in both [catalyst] and [EDA] and zero-order in [methyl acrylate], in agreement with the DFT-calculated mechanism. The calculated activation parameters corresponding to the rate-determining step of the reaction are in agreement with the experimental values, thus providing strong support for the proposed metalloradical mechanism.

The low temperature (-100 °C) single electron reduction of N1-phenylbenzotriazole in liquid ammonia, and the room temperature reduction of N1-phenylcyclooctatetraenotriazole in hexamethylphosphoramide, yields stable solutions of both anion radicals, which were studied via EPR spectroscopy. The amount of electron spin localized within the triazole ring, and how spin is distributed within this ring, is greatly influenced by the size of the annulene ring attached. UB3LYP/6-31++G(d,p) geometry optimizations using DFT methods were carried out for both anion radicals, and the calculated coupling constants (and electron spin densities) are in good agreement with the EPR spectroscopic results. Both theory and experiment show that much of the unpaired electron spin in the N1-phenylbenzotriazole anion radical is delocalized over the entire π system of benzotriazole ring including the phenyl ring attached, but that a significant percentage of total spin is found to reside within triazole ring with much of it located on the second nitrogen (N2). With the N1-phenylcyclooctatetraenotriazole anion radical, the majority of spin is localized over the π system of the COT ring, however a relatively small amount of total spin, found within the triazole moiety, is largely concentrated on two of the nitrogens (N1 and N3) within the ring.

A general, efficient and environmentally benign, one-step synthesis of substituted quinoline derivatives was achieved by acceptorless dehydrogenative coupling of o-aminobenzylalcohols with ketones and secondary alcohols catalyzed by a cheap, earth abundant and easy to prepare nickel catalyst [Ni(MeTAA)], featuring a tetraaza macrocyclic ligand (tetramethyltetraaza[14]annulene (MeTAA)). A wide variety of substituted quinolines were synthesized in high yields starting from readily available o-aminobenzylalcohols and ketones or secondary alcohols. A few controlled reactions were carried out to establish the acceptorless dehydrogenative nature of the reactions.

The vanadium-vanadium interactions in the polygonal aggregates of d1 vanadium(IV) atoms, with a total of 4k + 2 vanadium electrons (k an integer) imbedded in an electronically inactive borate matrix in certain vanadoborate structures are analogous to the ring carbon-carbon interactions in diamagnetic planar cyclic hydrocarbons. They thus represent a high-spin analogue of aromaticity. Thus, the vanadoborate anion [V6B20O50H8]8− with six V(IV) electrons (i.e., 4k + 2 for k = 1) contains a macrohexagon of d1 V(IV) atoms with four unpaired electrons. This high-spin system is related to the low-spin aromaticity in the diamagnetic benzene having six π electrons. Similarly, the vanadoborate anion [V10B28O74H8]16− with ten V(IV) electrons (i.e., 4k + 2 for k = 2) contains a macrodecagon of d1 V(IV) atoms with eight unpaired electrons. Again, this high-spin system is related to the aromaticity in the diamagnetic 1,6-methanol[10]annulene, having ten π electrons.

Nickel(II) complexes of [14]tetraazaannulene derivatives incorporating aromatic rings into their azaannulene framework were synthesized, and the anion-selectivity of the [14]tetraazaannulene nickel complexes 1 - 4 was evaluated by potentiometric measurements with solvent polymeric membrane electrodes. All of the [14]Tetraazaannulene nickel complexes, except 3, were found to exhibit high selectivity for the I(-) ion over the SCN(-) ion, although considerable interference of the ClO4(-) ion was observed in all 1 - 4 complexes. Concerning the anion-selectivities of 1 and 4, the incorporation of naphthalene rings into the azaannulene framework decreased not only the interference of the ClO4(-) ion but also the I(-) ion-selectivity over the SCN(-) ion. Comparison studies between the dibenzotetraaza[14]annulene nickel complexes 1 - 3 indicated that differences in the attached substituents of the [14]tetraazaannulene nickel complexes greatly influenced the ion-selectivity as ionophores. According to our computational results, the ionophoric properties of [14]tetraazaannulene nickel complexes 1 - 4 were influenced by their electrostatic properties rather than their topological properties.

In this study, π-conjugated molecular wires strapped by cyclic π-conjugated side chains were efficiently synthesized by the integration of dehydrobenzo[20]annulene units by intramolecular Glaser-type cyclization under high dilution conditions.

We investigated the self-assembled monolayers of octadehydrodibenzo[12]annulene (DBA) derivatives to see the effect of multiple intermolecular interactions on the formation of face-on vs edge-on configurations of planar compounds having weak core to core interactions at the liquid/graphite interfaces by means of scanning tunneling microscopy (STM). A DBA derivative having an N-dodecylamide chain at each end of the π-core formed face-on mode self-assemblies at the interfaces of both 1-phenyloctane (PO) and 1-octanoic acid (OA) and graphite. On the other hand, another DBA having both N-dodecylamide chains and methoxymethyl groups formed an edge-on mode self-assembly at the PO/graphite interface. However, at the OA/graphite interface, it formed a face-on mode self-assembly due to the solvent–molecule hydrogen bonds which suppress the intermolecular interactions. These results indicate that by multiple interactions between substituents the edge-on mode of self-assembly can be stabilized, rendering the otherwi...

To demonstrate key roles of multiple interactions between multiple components and multiple phases in the formation of an uncommon self-assembling pattern, we present here the construction of a porous hexagonal star (h-star) structure using a trigonal molecular building block at the liquid/ solid interface. For this purpose, self-assembly of hexaalkoxysubstituted dehydrobenzo[12]annulene derivatives DBA-OCns was investigated at the tetradecane/graphite interface by means of scanning tunneling microscopy (STM). Monolayer structures were significantly influenced by coadsorbed tetradecane molecules depending on the alkyl chains length (C13−C16) of DBA-OCn. However, none of DBA-OCn molecules formed the expected trigonal complexes, indicating that an additional driving force is necessary for the formation of the trigonal complex and its assembly into the h-star structure. As a first approach, we employed the “guest induced structural change” for the formation of the h-star structure. In the presence of two guest molecules, nonsubstituted DBA and hexakis(phenylethynyl)benzene which fit the respective pores, an h-star structure was formed by DBAOC15 at the tetradecane/graphite interface. Moreover, a tetradecane molecule was coadsorbed between a pair of alkyl chains of DBA-OC15, thereby blocking the interdigitation of the alkyl chain pairs. Therefore, the h-star structure results from the selfassembly of the four molecular components including the solvent molecule. The second approach is based on aggregation of perfluoroalkyl chains via fluorophilicity of DBA-F, in which the perfluoroalkyl groups are substituted at the end of three alkyl chains of DBA-OCn via p-phenylene linkers. A trigonal complex consisting of DBA-F and three tetradecane molecules formed an h-star structure, in which the perfluoroalkyl groups that orient into the alkane solution phase aggregated at the hexagonal pore via fluorophilicity. The present result provides useful insight into the design and control of complex molecular self-assembly at the liquid/solid interface. ispartof: Langmuir vol:31 issue:25 pages:7032-7040 ispartof: location:United States status: published

Chiral supramolecular architecture was synthesized from the achiral noncentrosymmetric title compound by using a twofold helical hydrogen-bonding network as a template.

Crossed McMurry reactions of bifuran- or bithiophenedicarbaldehydes with bipyrroledicarbaldehydes have been studied for the first time. Only those porphycenic macrocycles derived from homocoupled McMurry products were formed. The results are explained by using both density functional theory and electron propagator computations to model the electron affinity of the dialdehyde starting materials. It was predicted that bifuran\bithiophene cross-coupling would indeed occur, and this was demonstrated by the first synthesis of a novel dioxa,dithio hetero-porphycenoid annulene. This approach will allow the prior identification of viable substrates for related crossed McMurry reactions.

The cleavage of CC bonds in π-conjugated systems is an important method for controlling their shape and coplanarity. An efficient way for the cleavage of an aromatic CC bond in a typical buckybowl corannulene skeleton is reported. The reaction of 2-pyridylcorannulene with a catalytic amount of IrCl3 ⋅n H2 O in ethylene glycol at 250 °C resulted in a structural transformation from the curved corannulene skeleton to a strain-free flat benzo[ghi]fluoranthene skeleton through a site-selective CC cleavage reaction. This cleavage reaction was found to be driven by both the coordination of the 2-pyridyl substituent to iridium and the relief of strain in the curved corannulene skeleton. This finding should facilitate the design of carbon nanomaterials based on CC bond cleavage reactions.

The present article describes a DFT study of dibenzotetraaza[14]annulene complexed with first row transition metals (M II (DBTAA)), employing calculations made using the B3LYP hybrid functional with the Lanl2DZ/6-31G ∗ basis set. The parameters considered were bond distances and angles, electron configurations, interaction energies, vibrational frequencies, and frontier molecular orbitals (HOMO and LUMO). The calculations indicated that the key to complexes of the metals Ti, and Cr was the high spin state, while for Mn and Fe it was the intermediate spin state and for Co, Ni, Cu, and Zn it was the low spin state. The M–N distance (d(M–N)) and vibrational frequency showed inversely proportional behavior as a function of the atomic number of the metal. The Ni(DBTAA) complex showed the smallest d(M–N) and highest vibrational frequency, indicating greater compaction of the ligand on nickel. The interaction energy and the gap (HOMO–LUMO) were also calculated in order to estimate the stability and reactivity of the complexes. The stability increased with the atomic number of the central metal, in agreement with the Irving–Williams series, with Ni(DBTAA) being the most stable, and Ti(DBTAA) and Mn(DBTAA) being the most reactive of the complexes investigated.

Beyond rigorous inspection of the literature, selected comments and drawings from the Nozoe Autograph Books show how concepts and targets of the chemistry of today already existed 40 years ago. This is illustrated for the chemistry of carbo-mers, which was actually unknowingly inspired by chemists of the golden age. After a personal travel through time and pages by the last author of this essay, who meets autographs by people who have been important in his career, in particular on the occasions of Nozoe's visits to France or past ISNA events, unpublished results in non-benzenoid chemistry are dedicated to Nozoe's memory. Experimental advances are first disclosed on the comparative chemistry of the three ortho, meta and para isomers of tetraphenyl-carbo-benzene C18H2Ph4, the known ortho isomer serving as a reference. The two CH vertices of these chromophores make their [6]pericyclyne precursors quite sensitive and their yields and purifications challenging to optimize. The meta isomer was, however, isolated in 18% yield, and described by NMR and UV–vis absorption spectroscopy and crystallography. The para isomer was characterized both in pure form and in a 1:1 mixture with a single isomer of its HCl adduct, including by X-ray diffraction analysis of a co-crystal showing that the interior of the C18 ring of the HCl adduct is filled by the Cl atom. Theoretical advances are then offered regarding the “aromatic character” of a triple bond, by showing that the topological acyclic reference of acetylene is the Mobius-twisted cyclobutadiene. Acetylenoids are finally proposed as a novel class of non-benzenoid aromatics.

A C3-symmetric π-conjugated macrocycle combined with an appropriate hydrogen bonding module (phenylene triangle) allowed the construction of crystalline supramolecular frameworks with a cavity volume of up to 58%. The frameworks were obtained through non-interpenetrated stacking of a hexagonal sheet possessing three kinds of pores with different sizes and shapes. The activated porous material absorbed CO2 up to 96 cm(3) g(-1) at 195 K under 1 atm.

A square-planar Ni(II) dibenzotetraaza[14]annulene complex substituted with two 3,3-dimethylindolenine groups in the meso positions has recently been synthesized and characterized experimentally. In the solid-state, the Ni(II) complex forms linear π-interacting stacks with Ni···Ni separations of 3.448(2) Å. Measurements of the temperature dependence of the magnetic susceptibility revealed a drastic change in the magnetic properties at a temperature of 13 K, indicating a transition from low-to-high spin states. The molecular structures of the free-base ligand, the lowest singlet, and triplet states of the monomer and the dimer of the Ni complex have been studied computationally using density functional theory (DFT) and ab initio correlation levels of theory. In calculations at the second-order Møller-Plesset (MP2) perturbation theory level, a large energy of 260 kcal mol(-1) was obtained for the singlet-triplet splitting, suggesting that an alternative explanation of the observed magnetic properties is needed. The large energy splitting between the singlet and triplet states suggests that the observed change in the magnetism at very low temperatures is due to spin-orbit coupling effects originating from weak interactions between the fine-structure states of the Ni cations in the complex. The lowest electronic excitation energies of the dibenzotetraaza[14]annulene Ni(II) complex calculated at the time-dependent density functional theory (TDDFT) levels are in good agreement with values deduced from the experimental UV-vis spectrum. Calculations at the second-order algebraic-diagrammatic construction (ADC(2)) level on the dimer of the meso-substituted 3,3-dimethylindolenine dibenzotetraaza[14] annulene Ni(II) complex yielded Stokes shifts of 85-100 nm for the lowest excited singlet states. Calculations of the strength of the magnetically induced ring current for the free-base 3,3-dimethylindolenine-substituted dibenzotetraaza[14]annulene show that the annulene ring is very weakly antiaromatic, sustaining a paratropic ring-current strength of only -1.7 nA/T.

Based on spin-polarized first-principles density functional theory in conjunction with the nonequilibrium Green's function method, the spin transport properties of transition metal (TM)–dibenzotetraaza[14]annulene (DBTAA) complexes (TM = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) sandwiched between two Au electrodes are investigated. The results show that Fe– and Co–DBTAA can display perfect spin filtering behavior in a wide bias voltage region. Moreover, it is found that the connected position of anchoring groups on the complexes affect significantly the spin filtering efficiency. The observed spin filtering behavior is explained by the spin-resolved transmission spectrum and molecular projected self-consistent Hamiltonian state analyses.

We demonstrate the effective confinement of surface electrons in the pores of molecular networks formed by dehydrobenzo[12]annulene (DBA) molecules with butoxy groups (DBA-OC4) on Au(111). Investigation of the network formation starting from single molecules reveals a considerable interaction of the molecules with the substrate, which is at the origin of the observed confinement.

CCR2 and CCR5 receptors play a key role in the development and progression of several inflammatory, cardiovascular and autoimmune diseases. Therefore, dual targeting of both receptors appeals as a promising strategy for the treatment of such complex, multifactorial disorders. Herein we report on the design, synthesis and biological evaluation of benzo[7]annulene- and [7]annulenothiophene-based selective and dual CCR2 and CCR5 receptor antagonists. Intermediates were designed in such a way that diversification could be introduced at the end of the synthesis. Starting from the lead compound TAK-779 (1), the quaternary ammonium moiety was exchanged by different non-charged moieties, the 4-methylphenyl moiety was extensively modified and the benzo[7]annulene core was replaced bioisosterically by the [7]annulenothiophene system. The naphthyl derivative 9h represents the most promising dual antagonist (Ki (CCR2) = 25 nM, IC50 (CCR5) = 17 nM), whereas the 6-isopropoxy-3-pyridyl and 4-methoxycarbonylphenyl derivatives 9k and 9r show more than 20-fold selectivity for the CCR2 (Ki = 19 nM) over the CCR5 receptor.

The antiaromatic character of benzene in its first ππ* excited triplet state (T1) was deduced more than four decades ago by Baird using perturbation molecular orbital (PMO) theory [J. Am. Chem. Soc. 1972, 94, 4941], and since then it has been confirmed through a range of high-level quantum chemical calculations. With focus on benzene we now first review theoretical and computational studies that examine and confirm Baird's rule on reversal in the electron count for aromaticity and antiaromaticity of annulenes in their lowest triplet states as compared to Hückel's rule for the ground state (S0). We also note that the rule according to quantum chemical calculations can be extended to the lowest singlet excited state (S1) of benzene. Importantly, Baird, as well as Aihara [Bull. Chem. Soc. Jpn. 1978, 51, 1788], early put forth that the destabilization and excited state antiaromaticity of the benzene ring should be reflected in its photochemical reactivity, yet, today these conclusions are often overlooked. Thus, in the second part of the article we review photochemical reactions of a series of benzene derivatives that to various extents should stem from the excited state antiaromatic character of the benzene ring. We argue that benzene can be viewed as a molecular "Dr Jekyll and Mr Hyde" with its largely unknown excited state antiaromaticity representing its "Mr Hyde" character. The recognition of the "Jekyll and Hyde" split personality feature of the benzene ring can likely be useful in a range of different areas.

Ab initio calculations of the current density induced by an external magnetic field in altan-[10,5]coronene 3 (or altan(2)-[10]annulene) indicate the onset of a diatropic current on the outer loop (the "perimeter"), thus in contrast to the intentional design of altan-molecules. Spectral decomposition of the current shows that the failure of the altanisation design can be expected whenever the perimeter of the altan-molecule is of nearly the same size as that of the parent molecule. Equal lengths of these two perimeters always occur in iterated altan-molecules, which contain a cycloacenic fragment. Like longer polyacenes and cycloacenes, altan(2)-[10]annulene 3 and altan-kekulene 2 are predicted to have an open-shell singlet ground state.

Morphology of molecular aggregates is crucially affected by molecular shape and intermolecular interactions. In 2009, we reported the unusual gelation behaviour of a curved-butadiynyl-bridged cyclic pi-conjugated molecule, octadehydrodibenzo[12]annulene ([12]DBA), possessing two methyl ester groups in noncentrosymmetric positions. Aggregation of the [12]DBA derivative occurred anisotropically to give crystalline nanofibers, which finally formed an organogel. To investigate the aggregation behaviour of the related analogues, we synthesized octadehydrotribenzo[14]annulene ([14]DBA) derivatives with two and four methyl ester groups and revealed that the [14]DBAs gave not gels but crystals, in which the molecules are stacked not in a unidirectional manner but in an alternating way. The results indicate that the gelation and crystallization of the present molecular system is derived from the subtle balance of molecular shape and intermolecular interactions.

The accuracy of DFT methodology on modeling isotropic hyperfine coupling constants (hfccs or aiso) of conjugated radical cations containing 14N nucleus, intermediates involved in many biological and chemical processes, is investigated. A set of 222 hfccs, belonging to 50 radical species, are computed at the following levels of theory: PBE0/N07D, B3LYP/6-31G*, B3LYP/N07D, B3LYP/TZVP, and B3LYP/EPR-III, and compared to the available experimental values. In general, these five combinations of methods and basis sets estimate aiso(1H) in good agreement with experimental data. Conversely, selection of the basis set is of fundamental importance for accurate prediction of the 14N hfccs. A thorough analysis of the computed data allows us to establish that the best functional/basis set combination for obtaining accurate nitrogen coupling constants in conjugated radical cations is PBE0/N07D//B3LYP/6-31G*, which provides values with a discrepancy smaller than 1.5 G for most of constants. The model has been successfully tested on the calculation of 14N hfccs for different radical cation derivatives of syn-1,6:8,13-diimino[14]annulene, which is a highly demanding test because the strong experimental change in the aiso(14N) values critically depends on the local geometry of the diimino fragment which is function of the polymethylene chain length. Furthermore, a whole analysis of the computed structural parameters, NBO and distribution of the spin density of these annulene radicals has allowed to explain the huge increase of the aiso(14N) as well as their stability just for certain polymethylene chain length evidencing the formation of a N–N three electron σ bond.

In the present work, we have studied the gas phase one- and two-photon absorption (OPA and TPA) properties of the first two excited states of the triply twisted Möbius annulene molecule (G. R. Schaller, et al., Nat. Chem. 2014, 6, 608) and five model systems substituted with different donor and acceptor groups. The main purpose of this study is to explore the OPA and TPA properties of this newly synthesized molecule and the unique π-conjugation provided by it. We have used the linear and quadratic response theory methods with the CAMB3LYP functional and the cc-pVDZ basis set for calculating the required parameters. Our results indicate that in the absence of any directive force (i.e. the donor-acceptor groups) the unsubstituted molecule is completely TP inactive. However, as soon as we insert the donor-acceptor group the system becomes TP active which can further be enhanced (up to 3640 GM in our case) by changing the donor-acceptor groups. We have explained the results by performing a two-state model calculation and by analyzing the TP tensor elements and the orbitals involved in the transition processes.

The macrocyclic pillar ligand, dipyridyldibenzotetraaza[14]annulene (H2L), in the absence and presence of the dicarboxylate coligands, biphenyl-4,4′-dicarboxylic acid (H2bpdc) or benzene-1,3-dicarboxylic acid (H2bdc), reacts with nickel(II), cobalt(II) and zinc(II) to yield [Ni(L)] (1), [Co(L)] (2), [Co(L)]n (3), {[Zn(H2L)(bdc)]·0.5DMF·1.5H2O}n (4) and {[Co4(L)2(bpdc)2]·2DMF·H2O}n (5) displaying both discrete and polymeric structures. Complexes 1 and 2 are isostructural, with the respective low-spin, square-planar metal ions occupying the macrocyclic cavity and bound to the N4-donor set of the macrocycle in its doubly deprotonated form. In 3, the cobalt(II) centre again occupies the macrocyclic cavity, but in this case one axial site is occupied by a pyridyl nitrogen from a second ligand complex, resulting in the formation of an infinite zigzag one-dimensional (1D) structure. Solvothermal reaction between Zn(NO3)2·4H2O, H2L and H2bdc afforded the 2D coordination polymer {[Zn(H2L)(bdc)]·0.5DMF·1.5H2O}n (4) in which H2L ligands crosslink 1D (bdc-Zn)n wavy backbones via Zn–Npyd bonds. In contrast, the solvothermal reaction of H2L with Co(NO3)2·6H2O in the presence of H2bpdc resulted in formation of the 2-fold interpenetrated 3D coordination polymer, {[Co4(L)2(bpdc)2]·2DMF·H2O}n (5), exhibiting a pillared-layer structure. The 3D framework of 5 is based on dicobalt(II) cluster secondary building units (SBUs) to yield a rob net in which the bpdc/Co-based 2D nets are cross-linked by CoL macrocyclic pillar units; the framework of 5 is thermally stable until 350 °C.

A number of tetradehydrodinaphtho[10]annulene derivatives with varying charge transferring conduits between two naphthalene rings have been considered for the theoretical study of electronic structure and first hyperpolarizability. The BHHLYP, CAM-B3LYP and M06-2X methods along with the 6-311++G(d,p) basis set are used to calculate first hyperpolarizability by analytical evaluation of electric dipole second derivative. The results obtained by different methods are found to be consistent. The ground state polarity and the first hyperpolarizability of tetradehydrodinaphtho[10]annulene can be strongly enhanced by suitable modification of acetylene linkages. Using different ring structures containing electronegative atom(s) at the bridging position the extent of the longitudinal charge transfer and the magnitude of first hyperpolarizability can be enhanced strongly. The furan ring and the heteroazulene ring has been found to be the most effective bridging moieties to enhance the magnitude of static first hyperpolarizability. The variation of first hyperpolarizability has been explained satisfactorily in terms of the two state calculated spectroscopic properties.

Alkyne cross-metathesis of molybdenum carbyne complex [TolC≡Mo(OCCH3(CF3)2)3]·DME with 2 equiv of functional ynamines or ynamides yields the primary cross-metathesis product with high regioselectivity (>98%) along with a molybdenum metallacyclobutadiene complex. NMR and X-ray crystal structure analysis reveals that ynamides derived from 1-(phenylethynyl)pyrrolidin-2-one selectively cleave the propagating molybdenum species in the ring-opening alkyne metathesis polymerization (ROAMP) of ring-strained 3,8-dihexyloxy-5,6-dihydro-11,12-didehydrodibenzo[a,e][8]annulene and irreversibly deactivate the diamagnetic molybdenum metallacyclobutadiene complex through a multidentate chelate binding mode. The chain termination of living ROAMP with substituted ethynylpyrrolidin-2-ones selectively transfers a functional end-group to the polymer chain, giving access to telechelic polymers. This regioselective carbyne transfer strategy gives access to amphiphilic block copolymers through synthetic cascades of ROAMP followe...

A direct one‐pot synthesis of asymmetric dehydrobenzopyrido[12]annulenes 2 and 3 containing one or two pyridine rings is reported that employs a Stephens–Castro mediated cross‐coupling of mixtures of ethynylcuprate precursors. The spectroscopic and theoretical properties of 2 and 3 are compared to those of the threefold symmetric dehydrotribenzo[12]annulene 1, and dehydrotripyrido[12]annulenes 4 and 5 and dehydrodibenzodipyrido[16]annulene byproduct 6, and showed 1–5 to be essentially isoelectronic band gap materials whose electron accepting ability increases with increasing nitrogen incorporation. The structures of 2, 4 and 6 were also unambiguously characterized by X‐ray crystallography. The results highlight the potential dehydroaryl[12]annulenes incorporating pyridines offer for the construction of high carbon content electronic materials. Acknowledgement: The authors would to thank European Journal of Organic Chemistry for the opportunity to publish this article.

Functional π-systems with unusual opto-electronic properties are intensively investigated from both fundamental research and technological application viewpoints. This article reports on novel π-conjugated systems obtained by acetylenic and fullerene scaffolding. Linearly conjugated acetylenic nanorods, consisting of monodisperse poly(triacetylene) (PTA) oligomers and extending up to 18 nm length, were prepared to investigate the limits of effective conjugation and to explore at which length a monodisperse oligomer reaches the properties of an infinite polydisperse polymer. With the cyanoethynylethenes (CEEs), a powerful new class of electron acceptors is introduced that undergo intense intramolecular charge-transfer (CT) interactions with appended donors. Macrocyclic scaffolds with unusual opto-electronic properties are perethynylated dehydroannulenes, expanded radialenes, and radiaannulenes bearing peripheral dialkylanilino donor groups. Extended porphyrin-fullerene conjugates are investigated for their novel photophysical and efficient multicharge storage properties. Self-assembly of fullerenes and porphyrins, governed by weak interactions between the two components, leads to unprecedented nanopatterned surfaces that are investigated by scanning tunneling microscopy (STM).

Pharmaceutically and structurally important methanobenzo[7]annulenes were synthesized in very good yields with excellent enantio- and diastereoselectivities through an unprecedented organocatalytic formal [3+2] cycloaddition from readily available 2-alkyl-3-hydroxynaphthalene-1,4-diones and alkyl vinyl ketones.

In this paper, we report a general, efficient, and environmentally benign method for the one-pot cascade synthesis of quinazolin-4(3H)-ones via acceptorless dehydrogenative coupling of o-aminobenzamide with alcohols catalyzed by a simple Ni(II) catalyst, [Ni(MeTAA)], featuring a tetraaza macrocyclic ligand (tetramethyltetraaza[14]annulene (MeTAA)). A wide variety of substituted quinazolin-4(3H)-ones were synthesized in high yields starting from readily available benzyl alcohols and o-aminobenzamides. Several controlled reactions along with deuterium labeling studies were carried out to establish the acceptorless dehydrogenative nature of the reactions.

Two double-decker complexes with annulene ligands functionalized with indolenine groups were synthesized and characterized. The position of the proton acting as a counterion on one of the four indolenine nitrogen atoms was determined by using DFT calculations. Deprotonation and protonation of the complex induced by adding a base and an acid, respectively, were monitored by using NMR spectroscopy. Moreover, a correlation among the degree of protonation of the complex, the opening of the hysteresis, and the slow relaxation time is discussed.

Regioselective carbyne-transfer reagents derived from (3,3,3-trifluoroprop-1-yn-1-yl)benzene give access to functionalized ring-opening alkyne metathesis polymerization (ROAMP) initiators [R-C6H4C≡Mo(OC(CH3)(CF3)2)3] featuring electron-donating or -withdrawing substituents on the benzylidyne. Kinetic studies and linear free-energy relationships reveal that the initiation step of the ring-opening alkyne metathesis polymerization of 5,6,11,12-tetradehydrobenzo[a,e][8]annulene exhibits a moderate positive Hammett reaction constant (ρ = +0.36). ROAMP catalysts featuring electron-withdrawing benzylidynes not only selectively increase the rate of initiation (ki) over the rate of propagation (kp) but also prevent undesired intra- and intermolecular chain-transfer processes, giving access to linear poly-(o-phenylene ethynylene) with narrow molecular weight distribution. The regioselective carbyne transfer methodology and the detailed mechanistic insight enabled the design of a bifunctional ROAMP-reversible additi...

Nuclear magnetic shieldings have been calculated at the density functional theory (DFT) level for stacks of benzene, hexadehydro[12]annulene, dodecadehydro[18]annulene, and hexabenzocoronene. The magnetic shieldings due to the ring currents in the adjacent molecules have been estimated by calculating nucleus independent molecular shieldings for the monomer in the atomic positions of neighbor molecules. The calculations show that the independent shielding model works reasonably well for the H-1 NMR shieldings of benzene and hexadehydro[12]annulene, whereas for the larger molecules and for the C-13 NMR shieldings the interaction between the molecules leads to shielding effects that are at least of the same size as the ring current contributions from the adjacent molecules. A better agreement is obtained when the nearest neighbors are also considered at full quantum mechanical (QM) level. The calculations suggest that the nearest solvent molecules must be included in the quantum mechanical system, at least when estimating solvent shifts at the molecular mechanics (MM) level. Current density calculations show that the stacking does not significantly affect the ring current strengths of the individual molecules, whereas the shape of the ring current for a single molecule differs from that of the stacked molecules.

A new protocol for the catalytic synthesis of cyclopropanes using electron‐deficient alkenes is presented, which is catalysed by a series of affordable, easy to synthesise and highly active substituted cobalt(II) tetraaza[14]annulenes. These catalysts are compatible with the use of sodium tosylhydrazone salts as precursors to diazo compounds in one‐pot catalytic transformations to afford the desired cyclopropanes in almost quantitative yields. The reaction takes advantage of the metalloradical character of the Co complexes to activate the diazo compounds. The reaction is practical and fast, and proceeds from readily available starting materials. It does not require the slow addition of diazo reagents or tosylhydrazone salts or heating and tolerates many solvents, which include protic ones such as MeOH. The CoII complexes derived from the tetramethyltetraaza[14]annulene ligand are easier to prepare than cobalt(II) porphyrins and present a similar catalytic carbene radical reactivity but are more active. The reaction proceeds at 20 °C in a matter of minutes and even at −78 °C in a few hours. The catalytic system is robust and can operate with either the alkene or the diazo reagent as the limiting reagent, which inhibits the dimerisation of diazo compounds totally. The protocol has been applied to synthesise a variety of substituted cyclopropanes. High yields and selectivities were achieved for various substrates with an intrinsic preference for trans cyclopropanes.

Correction for ‘The aromaticity of dicupra[10]annulenes’ by Rafael Grande-Aztatzi et al., Phys. Chem. Chem. Phys., 2017, 19, 9669–9675.

An extensive theoretical investigation of the electronic structure of a tested fair model dicupra[10]annulene compound, based on the analysis of atom-pair delocalization indices, Bader's molecular graph, the inspection of the canonical molecular orbitals, the z components of their Nuclear Independent Chemical Shifts, NICS(0)zz, and the normalized Giambiagi multicenter delocalization indices, concludes that the perimeter aromaticity of the dicupra[10]annulene ring is consistent with both 10 and 14 π-electron Huckel aromatic 10-membered rings. In either case, the 10-membered ring encloses two 6 π-electron aromatic inner rings, hinged at the Cu-Cu bond. This work demonstrates that the aromaticity of dicupra[10]annulenes closely resembles that of naphthalene. Hence, they are best regarded as metalla-polyacenes, which could make the building blocks of extended structures such as metalated nanotubes.

A graphene nanoflake (GNF) is a polycyclic aromatic hydrocarbon (PAH) with a huge two-dimensional π-conjugated carbon material in which a central benzene ring is surrounded by identical benzene-type rings through infinite alternant method. In this paper, we explore the structure-aromaticity relationship of the GNFs and the GNFs with hollow sites (GNFHs) by combining the nucleus-independent chemical shifts (NICS) with the anisotropy of the current induced density (ACID). Firstly, the benzene is a typical aromatic molecule (NICS = -9.671 ppm), GNFs 1-6 is darned with benzene and the corresponding GNFHs 1'-6'. Secondly, the NICS values of GNFs 1-6 alternately vary: -1.214 (1) -13.847 (2) -2.662 (3) -14.530 (4) -3.932 (5) -13.978 (6) ppm, the GNFs (2, 4, 6) with even fragments of annulene have larger aromaticity than that of GNFs (1, 3, 5) with odd fragments of annulene. Significantly, the NICS values of GNFs 1-6 can also be fragment analyzed by the NICS values and ACID of benzene and corresponding GNFHs 1'-6'. The NICS values for GNFs (2, 4, 6) can be roughly estimated by the NICS value of benzene minus the NICS value of the GNFHs (2', 4', 6'), respectively. The NICS values for GNFs (1, 3, 5) can be roughly estimated by the NICS value of the GNFHs (1', 3', 5') minus the NICS value of benzene, respectively. We hope that the present work can provide a simple and reliable method for the rational design of the GNF with aromaticity, which may be used to understand the origin of the graphene nanoflake aromatic properties.

Highly conjugated hydrocarbons have attracted interest for use as active materials in electronic devices such as organic field effect transistors (OFET) and organic photovoltaics (OPV). In this Account, we review our progress in synthesizing and studying a new class of small molecules for potential use as organic semiconductors. The idea originated from prior research on octadehydrodibenz[12]annulene, as the system can undergo double transannular cyclization to yield the indeno[1,2-b]fluorene skeleton. Subsequent functionalization afforded the first stable, well-characterized indeno[1,2-b]fluorene derivatives, albeit in minute quantities (tens of milligrams). The preparation of these formally antiaromatic compounds has since been optimized: the new synthetic routes utilize inexpensive starting materials, involve robust and high-yielding transformations, and are amenable to considerably larger scale reaction. We have since researched the chemical space of indeno[1,2-b]fluorenes and related quinoidal structures by substitution with a number of functional groups and by permutation of the indenofluorene scaffold. These modifications have allowed us to explore fundamental concepts such as biradical character and antiaromaticity, important considerations when tuning electronic properties to yield functional organic materials. Altering the outer rings by exchange of carbocycles for heterocycles or by inclusion of additional rings as part of the fully conjugated skeleton is one strategy we have examined. Fusing these different aryl groups to s-indacene revealed a dependence of the antiaromaticity of the indacene core upon the outer group. Computational analysis of a series of indeno[1,2-b]fluorene derivatives uncovered an array of different levels of antiaromaticity in the core of the indeno[1,2-b]fluorene derivatives, with one of the benzothiophene derivatives calculated to be as antiaromatic as the parent s-indacene itself. Conversely, we have prepared compounds with expanded cores, starting with the naphthalene-based fluoreno[4,3-c]fluorene, which was produced through a similar route as the indeno[1,2-b]fluorene, using a dione as the key intermediate. Similar to indeno[1,2-b]fluorene, fluoreno[4,3-c]fluorene showed a closed shell ground state, with no evidence of open shell character even upon heating to 170 °C. Increasing the size of the quinoidal core to three rings afforded a diindeno[b,i]anthracene (DIAn) derivative, a compound with a much more complex electronic picture. To produce DIAn, a new synthetic route was devised involving a Friedel-Crafts alkylation to form the five-membered ring and a DDQ oxidation to produce the final compound. DIAn displayed NMR signals that were broadened at room temperature and disappeared when heated, indicative of a molecule with significant biradical character. Extensive computational and experimental investigation verified the controllable expression of its biradical character, with DIAn best described with a ground state that lies between a closed shell compound and a open-shell singlet biradical, with ready access to a thermally populated triplet state.

This work describes a DFT level theoretical quantum study using the B3LYP functional with the Lanl2TZ(f)/6-31G* basis set to calculate parameters including the bond distances and angles, electronic configurations, interaction energies, and vibrational frequencies of FeTClTAA (iron-tetrachloro-tetraaza[14]annulene), FeTOHTAA (iron-tetrahydroxy-tetraaza[14]annulene), FeTOCH3TAA (iron- tetramethoxy-tetraaza[14]annulene), FeTNH2TAA (iron-tetraamino-tetraaza[14]annulene), and FeTNO2TAA (iron-tetranitro-tetraaza[14]annulene) complexes, as well as their different spin multiplicities. The calculations showed that the complexes were most stable in the triplet spin state (S = 1), while, after interaction with carbon monoxide, the singlet state was most stable. The reactivity of the complexes was evaluated using HOMO–LUMO gap calculations. Parameter correlations were performed in order to identify the best complex for back bonding (3d xzFe → 2p xC and 3d yzFe → 2p zC) with carbon monoxide, and the degree of back bonding increased in the order: FeTNO2TAA

1,6-Methano[10]annulene solutions in cyclohexane have been subjected to continuous and pulsed UV irradiation. Photolysis occurs in both cases, giving naphthalene as a minor and major product, respectively. The wavelength dependence of the reaction in solution indicates that the photochemical process occurs, exciting 1,6-methano[10]annulene in the second and third singlet electronic excited states. The reaction kinetics has been determined under pulsed irradiation. From the time dependence of concentrations, along with support of density functional theory calculations and early published data, two mechanisms are proposed for naphthalene production. Reaction steps such as direct migration of the bridging methylene of 1,6-methano[10]annulene to cyclohexane and 1,6-methano[10]annulene isomerization to benzotropilidene have been identified. The calculated energy diagrams relative to the ground and lowest excited states allow one to relate these steps to processes such as electrocyclic closure and sigmatropic shift. The norcaradienic form of 1,6-methano[10]annulene results in the critical species for methylene migration and the sigmatropic [1,5] shift. The present results and those arising from photolysis in the gas phase are good examples of the photochemical reactivity of 1,6-methano[10]annulene.