Oxidative Intramolecular C-C Bond Formation Reactions of 1,2-Diarylbenzenes: Syntheses of Highly Conjugated Double-Bridged Polycyclic Aromatic Hydrocarbons

Oxidation reactions of 1,2-diarylbenzenes induce intramolecular C-C bond formation. The substrates studied here were prepared by the stepwise Suzuki-Miyaura coupling reaction that introduced 2-naphthyl, 2-anthranyl, and 2-pyrenyl groups on the ortho positions of benzene. The subsequent oxidation reaction with FeCl3 induced an oxidative C-C bond formation reaction in the interior regions of the molecules. In marked contrast to our previous observations, two C-C bonds were formed. Theoretical calculations indicated that large spin densities at the reaction positions of the bis(cation radical) and/or cation radical species are needed for the C-C bond formation. The π-expanded molecules obtained here showed bathochromic shifts in the absorption spectra and amphoteric multi-redox behavior in electrochemistry.

Zhang–Zhang Polynomials of Multiple Zigzag Chains Revisited: A Connection with the John–Sachs Theorem

Multiple zigzag chains Zm,n of length n and width m constitute an important class of regular graphene flakes of rectangular shape. The physical and chemical properties of these basic pericondensed benzenoids can be related to their various topological invariants, conveniently encoded as the coefficients of a combinatorial polynomial, usually referred to as the ZZ polynomial of multiple zigzag chains Zm,n. The current study reports a novel method for determination of these ZZ polynomials based on a hypothesized extension to John–Sachs theorem, used previously to enumerate Kekulé structures of various benzenoid hydrocarbons. We show that the ZZ polynomial of the Zm,n multiple zigzag chain can be conveniently expressed as a determinant of a Toeplitz (or almost Toeplitz) matrix of size m2×m2 consisting of simple hypergeometric polynomials. The presented analysis can be extended to generalized multiple zigzag chains Zkm,n, i.e., derivatives of Zm,n with a single attached polyacene chain of length k. All presented formulas are accompanied by formal proofs. The developed theoretical machinery is applied for predicting aromaticity distribution patterns in large and infinite multiple zigzag chains Zm,n and for computing the distribution of spin densities in biradical states of finite multiple zigzag chains Zm,n.

Multiconfiguration Pair-Density Functional Theory

Kohn-Sham density functional theory with the available exchange–correlation functionals is less accurate for strongly correlated systems, which require a multiconfigurational description as a zero-order function, than for weakly correlated systems, and available functionals of the spin densities do not accurately predict energies for many strongly correlated systems when one uses multiconfigurational wave functions with spin symmetry. Furthermore, adding a correlation functional to a multiconfigurational reference energy can lead to double counting of electron correlation. Multiconfiguration pair-density functional theory (MC-PDFT) overcomes both obstacles, the second by calculating the quantum mechanical part of the electronic energy entirely by a functional, and the first by using a functional of the total density and the on-top pair density rather than the spin densities. This allows one to calculate the energy of strongly correlated systems efficiently with a pair-density functional and a suitable multiconfigurational reference function. This article reviews MC-PDFT and related background information.

Reduction of dopant ions and enhancement of magnetic properties by UV irradiation in Ce-doped TiO2

We report the experimental observation of and theoretical explanation for the reduction of dopant ions and enhancement of magnetic properties in Ce-doped TiO2 diluted magnetic semiconductors from UV-light irradiation. Substantial increase in Ce3+ concentration and creation of oxygen vacancy defects in the sample due to UV-light irradiation was observed by X-ray and optical methods. Magnetic measurements demonstrate a combination of paramagnetism and ferromagnetism up to room temperatures in all samples. The magnetization of both paramagnetic and ferromagnetic components was observed to be dramatically enhanced in the irradiated sample. First-principle theoretical calculations show that valence holes created by UV irradiation can substantially lower the formation energy of oxygen vacancies. While the electron spin densities for defect states near oxygen vacancies in pure TiO2 are in antiferromagnetic orientation, they are in ferromagnetic orientations in Ce-doped TiO2. Therefore, the ferromagnetically-oriented spin densities near oxygen vacancies created by UV irradiation are the most probable cause for the experimentally observed enhancement of magnetism in the irradiated Ce-doped TiO2.

Theoretical Studies on the Reactions of Aryl and Hetaryl Thioketones with Nitrilimines

<p>Many synthetic routes to constructing biologically-active heterocyclic compounds are made feasible through the (3 + 2) cycloaddition 32CA reactions. Due to a large number of possible combinations of several heteroatoms from either the three-atom components (TACs) or the ethylene derivatives, the potential of the 32CA reactions in heterocyclic syntheses is versatile. Herein, the 32CA of thiophene-2-carbothialdehyde derivatives and <i>C</i>,<i>N</i>-disubstituted nitrilimines have been studied through density functional theory (DFT) calculations at the B3LYP/6-311G(d,p) level of theory. In the present study, one-step (3 + 2) and two-step (4 + 3) mechanisms of the addition of the TAC and ethylene derivative have been investigated. In all reactions considered, the one-step (3 + 2) cycloaddition is preferred over the two-step (4 + 3) cycloaddition. The TAC chemoselectively adds across the thiocarbonyl group present in the ethylene derivative in a (3 + 2) fashion to form the corresponding cycloadduct. Analysis of the electrophilic ( and nucleophilic ( Parr functions at the various reaction centers in the ethylene derivative show that the TAC adds across the atomic centers with the largest Mulliken atomic spin densities, which is in total agreement with the experimental observation. The selectivities observed in the title reaction are kinetically controlled.</p>

Theoretical Studies on the Reactions of Aryl and Hetaryl Thioketones with Nitrilimines

<p>Many synthetic routes to constructing biologically-active heterocyclic compounds are made feasible through the (3 + 2) cycloaddition 32CA reactions. Due to a large number of possible combinations of several heteroatoms from either the three-atom components (TACs) or the ethylene derivatives, the potential of the 32CA reactions in heterocyclic syntheses is versatile. Herein, the 32CA of thiophene-2-carbothialdehyde derivatives and <i>C</i>,<i>N</i>-disubstituted nitrilimines have been studied through density functional theory (DFT) calculations at the B3LYP/6-311G(d,p) level of theory. In the present study, one-step (3 + 2) and two-step (4 + 3) mechanisms of the addition of the TAC and ethylene derivative have been investigated. In all reactions considered, the one-step (3 + 2) cycloaddition is preferred over the two-step (4 + 3) cycloaddition. The TAC chemoselectively adds across the thiocarbonyl group present in the ethylene derivative in a (3 + 2) fashion to form the corresponding cycloadduct. Analysis of the electrophilic ( and nucleophilic ( Parr functions at the various reaction centers in the ethylene derivative show that the TAC adds across the atomic centers with the largest Mulliken atomic spin densities, which is in total agreement with the experimental observation. The selectivities observed in the title reaction are kinetically controlled.</p>

Exploiting Host-Guest Chemistry to Manipulate Magnetic Interactions in Metallosupramolecular M4L6 Tetrahedral Cages

<p>Reaction of Ni(OTf)₂ with the bisbidentate quaterpyridine ligand L results in the self-assembly of a tetrahedral, paramagnetic cage [Ni^II₄L₆]⁸⁺. By selectively exchanging the bound triflate from [OTfÌNi^II₄L₆](OTf)₇ (<b>1</b>), we have been able to prepare a series of host-guest complexes that feature an encapsulated paramagnetic tetrahalometallate ion inside this paramagnetic host giving [M^IIX₄ÌNi^II₄L₆](OTf)₆, where M^IIX₄²⁻= MnCl₄²⁻ (<b>2</b>), CoCl₄²⁻ (<b>5</b>), CoBr₄²⁻ (<b>6</b>), NiCl₄²⁻ (<b>7</b>), CuBr₄²⁻ (<b>8</b>) or [M^IIIX₄ÌNi^II₄L₆](OTf)₇, where M^IIIX₄⁻ = FeCl₄⁻ (<b>3</b>), FeBr₄⁻ (<b>4</b>). Triflate-to-tetrahalometallate exchange occurs in solution and can also be accomplished through single-crystal-to-single-crystal transformations. Host-guest complexes <b>1</b>-<b>8</b> all crystallise as homochiral racemates in monoclinic space groups, wherein the four {NiN₆} vertex within a single Ni₄L₆ unit possess the same Δ or Λ stereochemistry. Magnetic susceptibility and magnetisation data show that the magnetic exchange between metal ions in the host [Ni^II₄] complex, and between the host and the MX₄^n- guest, are of comparable magnitude and antiferromagnetic in nature. Theoretically derived values for the magnetic exchange are in close agreement with experiment, revealing that large spin densities on the electronegative X-atoms of particular {MX₄}ⁿ⁻ guest molecules leads to stronger host-guest magnetic exchange interactions. </p>

Exploiting Host-Guest Chemistry to Manipulate Magnetic Interactions in Metallosupramolecular M4L6 Tetrahedral Cages

<p>Reaction of Ni(OTf)₂ with the bisbidentate quaterpyridine ligand L results in the self-assembly of a tetrahedral, paramagnetic cage [Ni^II₄L₆]⁸⁺. By selectively exchanging the bound triflate from [OTfÌNi^II₄L₆](OTf)₇ (<b>1</b>), we have been able to prepare a series of host-guest complexes that feature an encapsulated paramagnetic tetrahalometallate ion inside this paramagnetic host giving [M^IIX₄ÌNi^II₄L₆](OTf)₆, where M^IIX₄²⁻= MnCl₄²⁻ (<b>2</b>), CoCl₄²⁻ (<b>5</b>), CoBr₄²⁻ (<b>6</b>), NiCl₄²⁻ (<b>7</b>), CuBr₄²⁻ (<b>8</b>) or [M^IIIX₄ÌNi^II₄L₆](OTf)₇, where M^IIIX₄⁻ = FeCl₄⁻ (<b>3</b>), FeBr₄⁻ (<b>4</b>). Triflate-to-tetrahalometallate exchange occurs in solution and can also be accomplished through single-crystal-to-single-crystal transformations. Host-guest complexes <b>1</b>-<b>8</b> all crystallise as homochiral racemates in monoclinic space groups, wherein the four {NiN₆} vertex within a single Ni₄L₆ unit possess the same Δ or Λ stereochemistry. Magnetic susceptibility and magnetisation data show that the magnetic exchange between metal ions in the host [Ni^II₄] complex, and between the host and the MX₄^n- guest, are of comparable magnitude and antiferromagnetic in nature. Theoretically derived values for the magnetic exchange are in close agreement with experiment, revealing that large spin densities on the electronegative X-atoms of particular {MX₄}ⁿ⁻ guest molecules leads to stronger host-guest magnetic exchange interactions. </p>