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Vapochromic crystals of Ni(II)–quinonoid complexes were theoretically investigated using density functional theory (DFT) calculations. Kato et al. previously reported that the purple crystals of a four-coordinate Ni(II)–quinonoid complex (1P) exhibited vapochromic characteristics upon exposure to methanol gas, resulting in orange crystals of the six-coordinate methanol-bound complex (1O) [Angew. Chem., Int. Ed.2017, 56, 2345–2349]. However, the authors did not characterize the crystal structure of 1P. In the present study, we computationally predicted the crystal structure of 1Pby performing a crystal structure search with classical force-field computations followed by optimization using DFT calculations. The simulated powder X-ray diffraction pattern of the DFT-optimized structure agreed with experimental observations, indicating that our predicted crystal structure is reliable. Investigation of the optimized crystal structure of 1Prevealed that its color change arose from changes in its 1D-band structure, which consists of Ni 3d orbitals and quinonoid π-orbitals. Intermolecular interactions were weakened upon the binding of methanol to the Ni(II) center in 1O. Consequently, the intermolecular 3d−π interaction in 1Plowered the band gap and induced the red-shifting of the monomeric four-coordinate Ni(II)–quinonoid complex. Meanwhile, the obtained absorption spectrum of 1Oclosely corresponded to that of the monomeric six-coordinate Ni(II)–quinonoid complex. Our study provides a new strategy for accurately predicting molecular crystal structures and reveals a new insight into vapochromism based on band structure color switching.

Reaction mechanisms of styrene polymerization, ethylene polymerization, and styrene–ethylene copolymerization catalyzed by the half-titanocene [(Me5C5)TiCl2(OAr)] complex were studied based on density functional theory (DFT) calculations. Neutral Ti(III), cationic Ti(IV), and ion-paired Ti(IV) [Ti(IV)-B(C6F5)4] complexes were examined as candidates of the active species in styrene and ethylene insertion reactions to investigate the influence of oxidation states in catalytic activity and selectivity. Our results clearly indicated that the cationic Ti(IV) species gives the highest catalytic activity for ethylene polymerization, which is consistent with previous studies. This is because of the higher Lewis acidity of the Ti(IV) center and the presence of a C–H agostic interaction to stabilize the transition state for the insertion reaction. On the other hand, only the neutral Ti(III) species is able to explain the high stereoselectivity in syndiospecific styrene polymerization (SSP), though both the Ti(III) and the Ti(IV) species are catalytically active for styrene polymerization. With the results from our previous XANES study, it is concluded that the neutral Ti(III) species produced by reduction of the Ti(IV) catalyst in the presence of styrene is the most plausible active species for SSP. In the Ti(IV) species, the activation energies of styrene and ethylene insertion reactions to polyethylene and ethylene insertion reaction to polystyrene were estimated to be very close to each other, suggesting that the Ti(IV) species is a plausible active species either for ethylene polymerization or styrene–ethylene copolymerization.

Gold (Au) clusters with well-defined geometrical structures have attracted substantial attention due to their unique optical and catalytic properties, which are drastically changed by the ligands, compositions, and geometric structures. Here, we investigated the effect of ligand on the electronic state of Au in [Au9(PPh3)8]3+(Au9) and [Au25(SC2H4Ph)18]−(Au25) by X-ray absorption spectroscopy using high energy resolution fluorescence detection (HERFD) and theoretical calculations. Au L3-edge X-ray absorption near-edge structure (XANES) spectra revealed that the white-line intensity of Au9was comparable to that of Au25, while the white-line peak of Au25was 3 eV lower than that of Au9. The total area of the white line of Au9corresponded to that of Au25, which is explained by the natural bond orbital analysis, showing that the occupancy of Au 5d orbitals of Au9was close to that of Au25. The simulated XANES spectra using finite difference method near-edge structure software resembled the experimental XANES spectra. The projected density of state profiles and molecular orbitals indicated that the unoccupied 5d orbitals of the surface Au in Au9and of surface and oligomer Au in Au25interacted with P/S 3s+3p orbitals. The difference in peak locations in Au L3-edge XANES between phosphine- and thiolate-protected gold clusters was ascribed to the energy shift of unoccupied Au 5d orbitals, which are modulated by the Au 5d and P/S 3s+3p interaction.

Four coordinate (arylimido)niobium(V) dimethyl complexes containing 2,6-di-tert-butylphenoxy ligand, Nb(NAr)Me2(O-2,6-tBu2C6H3) [Ar = 2,6-iPr2C6H3(5a), 2,6-Me2C6H3(5b), 2-MeC6H4(5c)], were prepared from the bis(dimethylamide) analogues, Nb(NAr)(NMe2)2(O-2,6-tBu2C6H3) (2a–c), by treatment with AlMe3. Structures with a distorted tetrahedral geometry of the bis(dimethylamide) complexes (2a–c) and the dimethyl complexes (5b,c) were determined by X-ray crystallography. The solution Nb K-edge XANES spectra (X-ray absorption near edge structure, in toluene at 25 °C) showed that pre-edge intensities in the dimethyl complexes (5a,b) were higher than those in the bis(dimethylamide) complexes (2a,b) and their pre-edge absorptions (including their shoulder edge absorptions) were highly affected by the ligand sets employed; these peak assignments are well explained by TD-DFT (time dependent density functional theory) simulation as a results of s–d transition and degree in subsequent d–p hybridization. The dimethyl complexes (5a–c) showed good catalysis capabilities for ethylene polymerization in n-octane in the presence of methylaluminoxane (MAO) especially at 80 °C (ca. 808–1140 kg-PE/mol-Nb·h). Treating 5awith [Ph3C][B(C6F5)4] in THF gave the cationic [Nb(N-2,6-iPr2C6H3)Me(O-2,6-tBu2C6H3)(THF)]+[B(C6F5)4]−(6a), which polymerized ethylene at 80 °C upon addition of Al(n-C8H17)3to afford ultrahigh molecular weight polymers with unimodal molecular weight distributions (Mn= 1.04–1.21 × 106, Mw/Mn= 1.60–1.86); the results strongly suggest that the polymerization proceeded via the cationic alkyl species.

Insights of environmental perturbation (an external electric field, EEF) are complicated but important in terms of experiments. In this paper, we report theoretical results of the effect of an EEF on olefin epoxidation by an Fe(IV)OCl–porphyrin complex using density functional theory. The EEF along the electron flow greatly affects the potential energy profile, and thereby affects the reaction mechanism and stabilization of the species. The results show that a negative EEF catalyzes ethylene epoxidation, whereas a positive EEF inhibits the reaction. Moreover, an EEF can exchange the ground state with the low-lying excited states. Therefore, the potential energy profile along the epoxidation reaction is mainly modified by the electron transfer from ethylene to the Fe(IV)OCl–porphyrin complex.Environmental perturbation (an external electric field, EEF) greatly affects the electronic structure and mechanism of olefin oxidation by oxoiron(IV) porphyrin catalyst along the O=Fe–Cl direction. Furthermore, the direction (positive and negative) of EEF affects the rate of the reaction by the easy or difficult electron transfer from ethylene to the Fe(IV)OCl–porphyrin.

Polyoxotantalates, clusters of tantalum (Ta) oxide, are promising catalysts for CO2fixation reactions because of their exceptional Lewis basicity facilitating CO2activation. Here, we unveiled the CO2activation on [H2Ta6O19]6–(Ta6) by high-energy-resolution fluorescence-detection (HERFD) X-ray absorption near-edge structure (XANES). The white line of Ta L3-edge HERFD-XANES identified three peaks not discernible with conventional XANES. In situ HERFD-XANES study of CO2adsorption on Ta6showed the disappearance of the high-energy shoulder peak and the emergence of a new lower-energy peak. Theoretical calculations showed that the three peaks before CO2adsorption correspond to transitions to molecular orbitals with high contributions from Ta 5d orbitals split by the ligand field of the distorted Ohsymmetrical {TaO6} units. The observed peak replacement reflects both destabilization of the dx2–y2orbitals and stabilization of the dz2orbital induced by centering from the off-center arrangement of {TaO6} units by the CO2attachment on terminal oxygen.

Mechanistic studies through Ti K-edge XANES and EXAFS spectra of the catalyst solution for 1-hexene polymerization using Cp*TiX2(O-2,6-iPr2C6H3) [X = Cl (1), Me (2)]–MAO catalysts and for syndiospecific styrene polymerization using (tBuC5H4)TiCl2(O-2,6-iPr2C6H3) (3)–MAO catalyst have been explored. Significant changes in the XANES spectrum (low energy shift in the edge peak, in addition to decrease in intensities of two pre-edge peaks) were observed when styrene (200 equiv) was added into a toluene solution containing 3and MAO, strongly suggesting that the complex 3[Ti(IV)] was reduced to Ti(III) by addition of styrene under these conditions. The EXAFS analysis suggests that the Ti–O bond (corresponding to coordination of phenoxide) was preserved along with dissociation of Ti–Cl bonds by treating with MAO. These XAS analysis data thus suggest that neutral Ti(III) species, (tBuC5H4)Ti(R)(OAr), play a role as the active species. The DFT-based computational analysis on the syndiospecific styrene insertion reaction also revealed that the neutral Ti(III) catalyst exhibits the lower activation energy than the others, strongly supporting the above mechanism. In contrast, no significant changes (in the oxidation state, basic structure) in the XANES spectra were observed when the toluene solution containing 1(or 2) was added MAO and 1-hexene, whereas preservation of the Ti–O bond along with dissociation of the Ti–Cl by treating with MAO was suggested through the EXAFS analysis.

Reaction mechanisms of hydrosilylation of ketone and alkene with tertiary silane using the Wilkinson-type catalyst were theoretically investigated on the basis of density functional calculations using ωB97XD functional. Previously proposed three mechanisms, the Chalk–Harrod (CH) mechanism, the modified Chalk–Harrod (mCH) mechanism, and the outer-sphere mechanism were examined. Besides, we also found two mechanisms, the alternative CH (aCH) mechanism and the double hydride (DH) mechanism. In the aCH mechanism, a four-coordinate rhodium hydride complex formed through the elimination of R3Si–Cl is a catalytically active species. In the DH mechanism, the active species is a six-coordinate complex with two Rh–H bonds. For the C═O double bond hydrosilylation, the rate-determining steps of the aCH and DH mechanisms are both acetone insertion into the Rh–H bond, and the order of the activation barrier is DH < aCH ≈ CH < mCH. For the C═C double bond hydrosilylation, except for the mCH pathway whose rate-determining step is the hydrosilane addition reaction, the rate-determining steps of the CH, aCH, and DH pathways are Si–C reductive elimination reactions. The order of the energy barrier is DH ≈ mCH < aCH ≈ CH. In the outer-sphere mechanism, no stable intermediate or transition state was found. Consequently, we concluded that the DH mechanism is adopted as the mechanism for the Rh-catalyzed hydrosilylation of the carbonyl group while the mCH or DH mechanism is adopted as the mechanism for alkenes under conditions where their active intermediates are formed. The present result revises a hypothesis that the hydrosilylation of the carbonyl group is in general accomplished by the mCH mechanism. The active species in the DH mechanism has one more extra Rh–H bond compared to that of the other pathways, and its interaction with a silyl group, trans-influence, and small steric effect are the origin of the highly efficient catalytic activity, which was not reported before.

Low-temperature complete oxidation of ethylene by the mesoporous silica-supported Pt catalyst is a forefront technology for food preservation. Public implementations of the Pt catalyst have already begun, and spectroscopy analyses on the catalytic mechanism have been reported. In this study, density functional theory calculations were conducted to clarify the potential energy profile and electronic mechanism of the catalytic reaction. Based on the experimental findings, a reaction pathway was proposed for ethylene oxidation up to CO2formation via the HCHO intermediate. Among several possibilities, a reaction pathway via ethylene dioxide species is energetically plausible for the C–C bond cleavage to generate HCHO. Particular focus was given to the electronic effect of the silica support in the ethylene dioxide route. The reservoir effect, in which the siloxide groups take electrons from the Pt moiety, reduces the activation energy of the C–C bond cleavage step by taking electrons from the σ(C–C) orbital.

A combination of iron(III) fluoride and 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (SIPr) catalyzes the high-yielding cross coupling of an electron-rich aryl chloride with an alkyl Grignard reagent, which cannot be attained using other iron catalysts. A variety of alkoxy- or amino-substituted aryl chlorides can be cross-coupled with various alkyl Grignard reagents regardless of the presence or absence of ß-hydrogens in the alkyl group. A radical probe experiment using 1-(but-3-enyl)-2-chlorobenzene does not afford the corresponding cyclization product, therefore excluding the intermediacy of radical species. Solution-phase X-ray absorption spectroscopy (XAS) analysis, with the help of density functional theory (DFT) calculations, indicates the formation of a high-spin (S= 2) heteroleptic difluorido organoferrate(II), [MgX][FeIIF2(SIPr)(Me/alkyl)], in the reaction mixture. DFT calculations also support a feasible reaction pathway, including the formation of a difluorido organoferrate(II) intermediate which undergoes a novel Lewis acid-assisted oxidative addition to form a neutral organoiron(IV) intermediate, which leads to an FeII/FeIVcatalytic cycle, where the fluorido ligand and the magnesium ion play key roles.Efficient cross-coupling reactions of various combinations of aryl chlorides with alkyl Grignard reagents were achieved by using an iron(III) fluoride/1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (SIPr) combination. Solution-phase X-ray absorption spectroscopy (XAS) and a density functional theory (DFT)-based mechanistic study suggest that a high-valent difluorido organoferrate(II), [MgX][FeIIF2(SIPr)(Me/alkyl)] is the catalytically active intermediate in an FeII/FeIVcatalytic cycle.

In this study, we investigated the role of solid electrolyte interface (SEI) films in the cells fabricated with the ionic liquids ([N2,2,1(2O1)][TFSI] and [Li(G4)][TFSI]). The SEI was introduced beforehand to the graphite electrode, which facilitated the intercalation of Li-ions into the graphite electrode in [Li(G4)][TFSI]. In addition, the discharge capacity in the case of the cell fabricated with [Li(G4)][TFSI] was almost similar to that observed in the case of the cell fabricated with organic electrolyte. The SEI performed the pulling apart combination of glyme and Li-ion. Identification analysis of the SEI component having action of extracting Li-ion from [Li(G4)] was carried out.

Numerous biomimetic molecular catalysts inspired by methane monooxygenases (MMOs) that utilize iron or copper-oxo species as key intermediates have been developed. However, the catalytic methane oxidation activities of biomimetic molecule-based catalysts are still much lower than those of MMOs. Herein, we report that the close stacking of a μ-nitrido-bridged iron phthalocyanine dimer onto a graphite surface is effective in achieving high catalytic methane oxidation activity. The activity is almost 50 times higher than that of other potent molecule-based methane oxidation catalysts and comparable to those of certain MMOs, in an aqueous solution containing H2O2. It was demonstrated that the graphite-supported μ-nitrido-bridged iron phthalocyanine dimer oxidized methane, even at room temperature. Electrochemical investigation and density functional theory calculations suggested that the stacking of the catalyst onto graphite induced partial charge transfer from the reactive oxo species of the μ-nitrido-bridged iron phthalocyanine dimer and significantly lowered the singly occupied molecular orbital level, thereby facilitating electron transfer from methane to the catalyst in the proton-coupled electron-transfer process. The cofacially stacked structure is advantageous for stable adhesion of the catalyst molecule on the graphite surface in the oxidative reaction condition and for preventing decreases in the oxo-basicity and generation rate of the terminal iron-oxo species. We also demonstrated that the graphite-supported catalyst exhibited appreciably enhanced activity under photoirradiation owing to the photothermal effect.

Potential energy profiles and electronic structural interpretation of the CO and H2binding reactions to molybdenocene and tungstenocene complexes [MCp2] (M = Mo and W, Cp = cycropentadienyl) were studied using density functional theory calculations and ab initio multiconfigurational electronic structure calculations. Experimentally observed slow H2binding was reasonably explained in terms of the spin-blocking effect. Electronic structural analysis at the minimum-energy intersystem crossing point (MEISCP) revealed that the singly occupied molecular orbital’s π-bonding/σ-antibonding character in the M-CO/H2moiety determines the energy levels of the MEISCP. Analysis of the reaction coordinate showed that the singlet-triplet gap significantly depends on the Cp-M-Cp angle. Therefore, not only the metal–ligand distance but also the Cp-M-Cp angle is an important reaction coordinate to reach the MEISCP, the transition state of H2binding. The role of spin–orbit coupling is also discussed.

This study proposes a marine biomass utilisation system and describes an anaerobic digestion system using marine biomass and food waste. Four scenarios are presented where the biomass amount varies and is sourced from different suppliers. Exergy is used for the feasibility evaluation. Various kinds of material and energy overall system are described in terms of exergy; exergy production and consumption is identified. The exergy efficiency of the overall system is introduced, and the efficiency of fossil fuel consumption is compared with the simple incineration of waste biomass. It is found that exergy production is bigger than exergy consumption and that the exergy of organic substances accounts for most of the exergy produced in all cases. From the viewpoint of fossil fuel consumption, the proposed system is more valuable than just the present system of incineration. This study provides a holistic viewpoint using exergy for the feasibility evaluation.

The authors retrospectively determined the prevalence of neck and shoulder symptoms (axial symptoms) after expansive laminoplasty with reattachment of spinous process and extensor musculature in patients with cervical myelopathy.

In this study, we investigated the role of solid electrolyte interface (SEI) films in the cells fabricated with the ionic liquids ([N2,2,1(2O1)][TFSI] and [Li(G4)][TFSI]). The SEI was introduced beforehand to the graphite electrode, which facilitated the intercalation of Li-ions into the graphite electrode in [Li(G4)][TFSI]. In addition, the discharge capacity in the case of the cell fabricated with [Li(G4)][TFSI] was almost similar to that observed in the case of the cell fabricated with organic electrolyte. The SEI performed the pulling apart combination of glyme and Li-ion. Identification analysis of the SEI component having action of extracting Li-ion from [Li(G4)] was carried out.

The DFT computational geometry and CO stretching frequency of the active center of iron sulfur cluster free hydrogenase (Hmd) indicate that the active site contains low-spin Fe(II) center coordinated with two COs, cysteine, either acylpyridone and water or acylpyridinol and hydroxide.