Anisotropy Of The Current-induced Density Research Articles

Understanding the effects of building block rings of π electron-rich organic photocatalysts in CO2 transformation to amino acids

Understanding the effective factors in the performance of some Oligo (p-phenylenes) (OPPs) and Polycyclic Aromatic Hydrocarbons (PAHs), as efficient organocatalysts in photocatalytic CO2 transformations are the main goals of this investigation. The studies are based on density functional theory (DFT) calculations on the mechanistic aspects of C–C bond formation through a coupling reaction between CO2•– and amine radical. The reaction is performed through two successive single electron transfer steps. After careful kinetic investigations by Marcus’ theory rules, powerful descriptors are used to describe the behavior of observed barrier energies of electron transfer steps. The studied PAHs and OPPs consist of different numbers of rings. Thus, it can be considered different charge densities, afforded from π electrons, of PAHs and OPPs that cause distinguished efficiency in kinetic aspects of electron transfer steps. Electrostatic Surface Potential (ESP) analyses reveal a good relationship between the charge density of the studied organocatalysts in single electron transfer (SET) steps and the kinetic parameters of the steps. Moreover, the contribution of rings in the framework of PAHs and OPPs would be another effective factor in the barrier energies of SET steps. Aromatic properties of the rings, studied by the Anisotropy of the Current-Induced Density (ACID), Nucleus-Independent Chemical Shift (NICS), the multi-center bond order (MCBO), and AV1245 Indexes, are the other impressive factors in the role of rings in SET steps. The results show that the aromatic properties of the rings are not similar to each other. Higher aromaticity affords remarkable reluctance of the corresponding ring to participate in SET steps.

Bonding character, electronic properties, and electronic transitions of perfluorocubane as a small electron acceptor.

Perfluorocubane is a fluorinated analogue of a polyhedral hydrocarbon observed recently in experiment (M. Sugiyama, M. Akiyama, Y. Yonezawa, K. Komaguchi, M. Higashi, K. Nozaki and T. Okazoe, Electron in a cube: Synthesis and characterization of perfluorocubane as an electron acceptor, Science, 2022, 377, 756-759). Inspired by its unique structure and electronic properties, we systematically explored its chemical stabilities, bonding character, electronic properties, and electronic transitions using density functional theory calculations. Analysis of the binding energies and Mayer bond orders reveals that the C8F8 molecule has high chemical stability with a special electronic structure, and the addition of an extra electron to the neutral molecule may generate a radical anion with a hosted electron inside the cubane frame. The induced ring currents under an external magnetic field reveal that perfluorocubane exhibits an overall small diamagnetic current supported by anisotropy of the current-induced density (ACID) and gauge-including magnetically induced currents (GIMIC). AdNDP analysis indicates that the localized two-center two-electron (2c-2e) σ-bonds are responsible for structural stabilization of the molecule. Further study into the electronic excitations shows that the main electronic transitions of perfluorocubane come from the surface of the cubic frame to its inner structure. Consequently, perfluorocubane can be recognized as a small electron acceptor material due to its special electron-carrying capacity, which will promote further applications of novel conducting and semiconducting materials.

Light‐ and Heat‐Controlled Formation of Osmanaphthalenes and Osmanaphthalynes

Comprehensive SummarySimple and efficient synthesis of metalla‐aromatics with tailored distinctive optical, magnetic, redox, and light‐emitting properties is attractive yet challenging. We have now successfully synthesized three paramagnetic osmanaphthalenes bearing different electron‐donating groups as well as the first osmabenzo[b]carbazole containing an osmanaphthalene unit with four fused rings in good yields by subjecting suitable osmium carbyne precursors to a visible‐light‐induced protocol. In contrast, the four corresponding diamagnetic cyclic metal carbynes containing an osmanaphthalyne unit were obtained from the same osmium carbyne precursors by a heating method. The lowest‐energy absorptions of the paramagnetic osmanaphthalenes are red‐shifted compared to the corresponding osmanaphthalynes. Additionally, experimental observations including X‐ray analysis as well as nucleus‐independent chemical shift (NICS), anisotropy of the current‐induced density (AICD) calculations revealed these novel osmapolycycles bearing phosphonium substituents to be of aromatic character.

Predicting dinitrogen activation by borenium and borinium cations.

The activation of thermodynamically stable and kinetically inert dinitrogen (N2) has been a great challenge due to the significant strength of the triple bond. Recently, in an experimental study on N2 activation by boron species, a highly reactive two-coordinated borylene broke through the limitations of traditional strategies of N2 activation by metal species. Still, studies on metal-free N2 activation remain underdeveloped. Here, we systematically investigate a frustrated Lewis pair (FLP) combining carbene and borenium (or borinium) cations to screen potential candidates for N2 activation via density functional theory calculations. As a result, we found that two FLPs (closed form FLP, borenium and open form FLP, borinium) are able to activate N2 in a thermodynamically and kinetically favorable manner, with a low energy barrier of 9.6 and 7.3 kcal mol-1, respectively. Furthermore, aromaticity was found to play an important role in the stabilization of the products, supported by nucleus-independent chemical shift (NICS), anisotropy of the current-induced density (ACID) and electron density of delocalized bonds (EDDB) analysis. Our findings provide an alternative approach for metal-free N2 activation, highlighting the importance of FLP chemistry and aromaticity in N2 activation.

Electronic structures of zinc octaalkylthio- and octaphenylthio-tetrapyrazinoporphyrazines, and comparison with those of phthalocyanines and pyrazinoporphyrazines

Eight strongly electron-donating alkylthio- or arylthio-groups have been introduced to a strongly electron-withdrawing pyrazinoporphyrazine (PyZ) core, to form the Zn complexes of octadecylthiolated ZnPyZ, (SDc)[Formula: see text]ZnPyZ, and octaphenylthiolated ZnPyZ, (S[Formula: see text])[Formula: see text]ZnPyZ, and their electronic structures studied by 1H NMR and electronic absorption spectroscopy. The strength of the ring current, aromaticity, and flow of charge were discussed by calculating the ring current, nucleus-independent chemical shift (NICS), and anisotropy of the current-induced density (ACID), respectively. Good agreement was seen for the results of these three calculations, demonstrating that a strong ring current of the macrocycle is produced when the aromatic ring fused to the tetraazaporphyrin core has a weaker diamagnetic ring current, [Formula: see text]. weaker aromaticity (negatively smaller NICS values). TD-DFT molecular orbital (MO) calculations succeeded in explaining the differences of the absorption spectra between these octathiolated ZnPyZs and those without thiolated groups. The singlet oxygen quantum yield in pyridine (0.62) of (S[Formula: see text])[Formula: see text]ZnPyZ was similar to that (0.61) of normal ZnPc.

Dioxygen Activation by Internally Aromatic Metallacycle: Crystallographic Structure and Mechanistic Investigations.

SummaryMononuclear metal-peroxo species are invoked as the key intermediates in metalloenzymatic or synthetic catalysis. However, either transience or sluggishness reactivity of synthetic analogs of metal-peroxo species impedes our understanding of oxygen activation mechanism. Herein, we designed and characterized a dioxygen-derived mononuclear osmium-peroxo complex, in which the peroxo ligand is stabilized by internally aromatic metallacycle. We demonstrate that the osmium-peroxo species shows catalytic activity toward promoterless alcohol dehydrogenations. Furthermore, computational studies provide a new mechanism for the osmium-peroxo-mediated alcohol oxidation, starting with the concerted double-hydrogen transfer and followed by the generation of osmium-oxo species. Interestingly, the internally aromatic metallacycle also plays a vital role in catalysis, which mediates the hydrogen transfer from osmium center to the distal oxygen atom of Os–OOH moiety, thus facilitating the Os–OOH→Os=O conversion. We expect that these insights will advance the development of aromatic metallacycle toward aerobic oxidation catalysis.

Achieving Adaptive Aromaticity in Cyclo[10]carbon by Screening Cyclo[n]carbon (n=8-24).

Discovery of species with adaptive aromaticity (being aromatic in both the lowest singlet and triplet states) is particularly challenging as cyclic species are generally aromatic either in the ground state or in the excited state only, according to Hückel's and Baird's rules. Inspired by the recent realization of cyclo[18]carbon, here we demonstrate that cyclo[10]carbon possesses adaptive aromaticity by screening cyclo[n]carbon (n=8-24), which is supported by nucleus-independent chemical shift (NICS), anisotropy of the current-induced density (ACID), π contribution of electron localization function (ELFπ ) and electron density of delocalized bonds (EDDB) analyses. Further study reveals that the lowest triplet state of cyclo[10]carbon is formed by in-plane ππ* excitation. Thus, the major contribution to the aromaticity from out-of-plane π molecular orbitals does not change significantly in the lowest singlet state. Our findings highlight a crucial role of out-of-plane π orbitals in maintaining aromaticity for both the lowest singlet and triplet states as well as the aromaticity dependence on the number of the carbon in cyclo[n]carbon.

Theoretical study on desulfurization mechanisms of a coal-based model compound 2-methylthiophene during pyrolysis under inert and oxidative atmospheres

Density functional theory (DFT) was used to investigate the desulfurization mechanisms of 2-methylthiophene (2-MT) during pyrolysis under inert and oxidative atmospheres. 12 possible reaction pathways were calculated and the feasibility of each reaction was analyzed from the perspective of thermodynamics and kinetics. The calculated results show that a H and S can promote 2-MT pyrolysis under inert atmosphere. The reaction temperatures and the highest energy barriers decrease significantly when one H and S participating in 2-MT pyrolysis process. The reason is that H and S can eliminate aromaticity of 2-MT by anisotropy of the current-induced density (ACID) analysis and reduce structural stability of 2-MT molecule. Pyrolysis desulfurization of 2-MT is thermodynamically more favorable under oxidative atmosphere than inert atmosphere. Furthermore, for COS formation, the desulfurization mechanism is more kinetically favorable initiated by alkyl side chain than by thiophene ring. For SO2 formation, it is more kinetically and thermodynamically favorable for the desulfurization mechanism initiated by Diels-Alder cycloaddition between bimolecular 2-MT sulfones than by single 2-MT sulfone decomposition. Additionally, the rate constants of COS formation are much smaller than that SO2 formation at a certain temperature. This also explains why SO2, rather than COS, is the main sulfur-containing gas product during 2-MT pyrolysis under oxidative atmosphere.

Planar Antiaromatic Core-Modified 24π Hexaphyrin(1.0.1.0.1.0) and 32π Octaphyrin(1.0.1.0.1.0.1.0) Bearing Alternate Hybrid Diheterole Units.

The Lewis acid catalyzed self-condensation of hybrid diheterole (furan-pyrrole and thiophene-pyrrole) precursors has afforded novel Hückel antiaromatic 24π hexaphyrin(1.0.1.0.1.0) and 32π octaphyrin(1.0.1.0.1.0.1.0) structures without β-annulated bridges. Single-crystal X-ray diffraction analysis of the hybrid porphyrinoids (S3 N3 -ox and O4 N4 -ox) revealed a nearly planar conformation and the 1 H NMR spectra suggest the presence of paratropic ring currents. These antiaromatic macrocycles show characteristic optical features and underwent reversible two-electron reduction to Hückel aromatic 26π- and 34π-electron species, respectively, as is evident from the results of spectroscopic and theoretical studies (nucleus-independent chemical shift (NICS) and anisotropy of the current-induced density (ACID) calculations). The incorporation of hybrid diheteroles alternately into expanded porphyrin skeletons provides a novel approach to the fine-tuning of the electronic structures of planar antiaromatic macrocycles.

Aromaticity of graphene nanoflakes in a new way: fragment analysis by combination of the nucleus-independent chemical shifts and the anisotropy of current induced density.

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=-9.671ppm), 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.

A MP2 and DFT study of the aromatic character of polyphosphaphospholes. Is the pyramidality the only factor to take into consideration?

A comprehensive MP2/6-311 + G(d,p) and B3LYP/6-311 + G(d,p) study of the aromatic character of phospholes, P(n)(CH)(4-n )PH with n = 0-4 was conducted. For this purpose, the structures for these compounds were optimized at both theoretical levels and different magnetic properties (magnetic susceptibility anisotropy, χ(anis), and the nucleus-independent chemical shifts, NICS) were evaluated. For comparison, these magnetic properties were also calculated in the optimized structures with planarity constraints. We have also applied the ACID (anisotropy of the current-induced density) method in this analysis. The main conclusions are the aromatic character of these compounds, the relationship between aromaticity and planarity and the importance of other factors in this aromaticity.

A theoretical study of the influence of BF 3 on the reaction path of the [4+2] cycloaddition of vinylketene with formaldimine

A comprehensive B3LYP/6-31+G ∗ study of the influence of BF 3 on the [4+2] cycloaddition of vinylketene with formaldimine was conducted. For this purpose, the complete pathway was determined and changes in different magnetic properties (magnetic susceptibility, χ, magnetic susceptibility anisotropy, χ anis, and the nucleus-independent chemical shifts, NICS) were monitored along the reaction profile with a view to estimate the aromatization associated to the process. We have also applied the ACID (anisotropy of the current-induced density) method with the same intention.

A DFT study of the [4+2] cycloadditions of conjugated ketenes (vinylketene, imidoylketene and formylketene) with formaldimine. The pericyclic or pseudopericyclic character from magnetic properties

A comprehensive B3LYP/6-31+G ∗ study of the nature of the [4+2] cycloadditions of conjugated ketenes, vinylketene, imidoylketene and formylketene, with formaldimine was conducted. For each reaction, the complete pathway was determined and changes in different magnetic properties (magnetic susceptibility, χ, magnetic susceptibility anisotropy, χ anis, and the nucleus-independent chemical shift, NICS) were monitored along the reaction profile with a view to estimate the aromatization associated to the process. We have also applied the ACID (anisotropy of the current-induced density) method with the same purpose. The deep analysis of the results indicates the existence of both disrotatory and conrotatory pericyclic paths for the cyclization step of the cycloaddition of vinylketene with formaldimine and the pseudopericyclic character of reactions with imidoylketene and formylketene.

A Comparative Theoretical Study of the Pericyclic-pseudopericyclic Character in a Group of Cyclizations of Dienylketenes to Cyclohexadienones

A comprehensive B3LYP/6-31+G* study of the nature of 6pi electrocyclizations of four different dienylketenes (2-furanyl, 2-pyrrolyl, cyclopenta-1,3-dienyl, and 2-thiophenyl-substituted ketenes) to corresponding cyclohexadienones was carried out. An analogous system ((3Z)-4-(3H-pyrrol-2-yl)buta-1,3-dien-1-one) was also analyzed. For this purpose, the complete pathways were determined (reactants, products, transition states, and the IRC connecting reactants and products), and changes in different magnetic properties (magnetic susceptibility, chi, magnetic susceptibility anisotropy, chi anis, and the nucleus-independent chemical shifts, NICS) were monitored along the reaction profiles with a view to estimating the aromatization associated to the processes. We have also applied the ACID (anisotropy of the current-induced density) method with the same intention. The deep analysis of the results indicates a pericyclic character of the processes for the dienylketenes despite the relatively small NICS values in the transition states. Only the reaction of (3Z)-4-(3H-pyrrol-2-yl)buta-1,3-dien-1-one presents pseudopericyclic character due to the in-plane attack of the lone pair on nitrogen.

A computational study of the electrocyclization of o-divinylbenzene and derivatives

Electrocyclization reactions of o-divinylbenzene and several derivatives were studied by performing density functional theory (DFT) calculations together with the 6-31+G ∗ basis set. Reactants, products and transition states for each reaction were localized and the path connecting reactants and products was also obtained. Along the reaction path, magnetic properties were evaluated to elucidate the characteristics of the reactions studied. Considering the overall results obtained with different indexes, such as magnetic susceptibility, nucleus independent chemical shift (NICS) or anisotropy of the current-induced density (ACID), all the reactions were found to keep the main characteristics of pericyclic reactions, showing an enhanced aromaticity in the vicinity of the transition state. Only two cyclizations, involving an isocyanate or ketene group, arose some doubts about their behaviour, but both still showed characteristics of pericyclic reactions, though weakened with respect to prototypical electrocyclizations as that of o-divinylbenzene.

A DFT Study of the Concerted Cyclisation of 3‐Azidopropenal to Isoxazole:Is it a Pseudopericyclic Reaction According to Its Magnetic Properties?

AbstractA comprehensive B3LYP/6‐31+G(2d,p) study of the nature of the concerted cyclisation of 3‐azidopropenal to isoxazole was conducted. For this purpose, the complete pathway was determined and changes in different magnetic properties [magnetic susceptibility (χ), magnetic susceptibility anisotropy (χanis) and the nucleus‐independent chemical shifts (NICS)] were monitored along the reaction profile with a view to estimating the aromatisation associated with the process. We have also applied the ACID (anisotropy of the current‐induced density) method with the same intention. Analysis of the results in depth indicates a pseudocoarctate character for this reaction. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2005)

Are Electrocyclization Reactions of (3Z)-1,3,5-Hexatrienone and Nitrogen Derivatives Pseudopericyclic? A DFT Study

[reactions: see text] Electrocyclization reactions of (3Z)-1,3,5-hexatrienone and nitrogen derivatives were studied by performing density functional theory (DFT) calculations together with the 6-31+G* basis set. Reactants, products, and transition states for each reaction were localized and the IRC connecting reactants and products was also obtained. Magnetic properties were evaluated along the reaction path to elucidate the characteristics of the reactions studied. As obtained from the calculations, electrocyclization of (3Z)-1,3,5-hexatrienone is a pericyclic process, as indicated by a variety of indexes, such as Nucleus Independent Chemical Shift (NICS), anisotropy of the magnetic susceptibility, or anisotropy of the current-induced density (ACID). This reaction presents characteristics of pericyclic reactions despite the activation energy lowering relative to the electrocyclization of (4Z)-1,2,4,6-heptatetraene, and the relatively small NICS values observed in the transition state. Magnetic properties indicate that an enhancement of the aromaticity relative to reactants and products occurs revealing the absence of orbital disconnections on the cyclic loop of interacting orbitals. Only two reactions among those studied exhibit pseudopericyclic character due to the in-plane attack of the lone pair on nitrogen. In these cases, the reactions showed no barrier for the electrocyclization process, and no aromaticity enhancement was observed.

A DFT study of the Boulton-Katritzky rearrangement of (5R)-4-nitrosobenz[c]isoxazole and its anion: pseudopericyclic reactions with aromatic transition states.

The nature of the Boulton-Katritzky rearrangement of (5R)-4-nitrosobenz[c]isoxazole and its anion was studied employing three methodologies: calculation of magnetic properties (magnetic susceptibility, magnetic susceptibility anisotropy, and the nucleus-independent chemical shifts), the natural bonding orbital analysis, and the ACID (anisotropy of the current-induced density) method. The deep analysis of the results indicates a pseudopericyclic character for these reactions despite the aromaticity of the transition states.

Delocalization of Electrons in Molecules

We report a general method for the investigation and quantification of delocalization in molecules. The method is based on the anisotropy of the current-induced density (ACID). Compared to the current density, which has been frequently used to investigate delocalization, the ACID approach has several advantages: it is a scalar field which is invariant with respect to the relative orientation of the magnetic field and the molecule, it is not a simple function of the overall electron density, it has the same symmetry as the wave function, and it can be plotted as an isosurface. Several selected examples demonstrate the predictive power and the general applicability of this method.