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Niobium perovskite oxynitrides are emerging as promising semiconductor materials for solar energy conversion processes, due to their physical properties and amenability to defect engineering. However, defect engineering in mixed-anion semiconductors such as perovskite oxynitrides is generally hindered by the absence of long-range order in the crystal lattice, a phenomenon known as anion-ordering. We demonstrate how anion ordering influences the stability and mobility of point defects in two exemplar perovskite oxynitrides, BaNbO2N and LaNbON2. Accurate first-principles calculations show that fully cis-anion orderings in BaNbO2N are more stable than fully trans-anion orderings, whereas anion orderings with mixed dimensionality may be more prevalent in the lower-symmetry LaNbON2. Anion ordering in LaNbON2 is also influenced by a pronounced A-site coordination sphere effect not observed in BaNbO2N, whereby local La-(O,N)12 coordination environments give rise to alternating LaO and LaN layers in the bulk material. Anion order was predicted to effect the redistribution of electrons upon anion vacancy creation to the cation sublattice. Diffusion barriers for O2− vacancies in trans-ordered BaNbO2N were found to be lower than those for N3− vacancies, suggesting that stabilising trans-ordered phases of BaNbO2N will yield more effective retention of nitrogen content in this material. The reverse is the case for LaNbON2, with N3− vacancy defects exhibiting more facile diffusion than O2− vacancy defects. We believe these insights will aid the emergent understanding of defect engineering in mixed-anion perovskite oxynitride semiconductors, and specifically help facilitate strategies for stabilising their nitrogen content.

Described herein is the development of an unprecedented approach to direct amination of unstrained aryl-ketone Csp2-Csp2 sigma bonds with sulfonylazides via Rh(III)-catalyzed Csp2-Csp2 cleavage. Th...

Lewis acid transition-metal-complex-catalyzed hydrosilylation of CO2 has attracted vast interests. Yet, the Si–H bond activation mechanism is still ambiguous and needs further elucidation. Herein, ...

A Co(II)-catalyzed pyridyl C-H bond carbenoid insertion with α-diazoacetates has been realized. This transformation features a highly regioselective C-C bond formation at the C3-position of pyridines, providing an efficient access to diverse α-aryl-α-pyridylacetates.

Sila-molecules have recently attracted attention due to their promising applications in medical and industrial fields. Compared with all-carbon parent compounds, the different covalent radius and electronegativity of silicon from carbon generally endow the corresponding sila-analogs with unique biological activity and physicochemical properties. Vinylsilanes feature both silyl-hyperconjugation effect and versatile reactivities, developing vinylsilane-based Smiles rearrangement will therefore provide an efficient platform to assemble complex silacycles. Here we report a practical Ir(III)-catalyzed cycloaromatization of ortho-alkynylaryl vinylsilanes with arylsulfonyl azides for delivering naphthyl-fused benzosiloles under visible-light photoredox conditions. The combination of experiments and density functional theory (DFT) energy profiles reveals the reaction mechanism involving α-silyl radical Smiles rearrangement., Arene-fused siloles have attracted interest due to their promising applications in electronic and optoelectronic devices. Here, the authors report Ir(III)-catalyzed cycloaromatization of ortho-alkynylaryl vinylsilanes with arylsulfonyl azides via α-silyl radical Smiles rearrangement for accessing naphthyl-fused benzosiloles under visible-light photoredox conditions.

Cost-efficient ruthenium complexes are prominent catalysts for many important chemical processes, leading to a challenge in chemoselective control for Ru catalysis. A series of half-sandwich ruthenium(II) complexes with diverse N,N-bidentate ligands showed intriguing chemoselectivity in the catalyzed reductive hydration of alkynes. To reveal the ligand effects on chemoselective control, DFT calculations were performed to systematically study their detailed mechanisms. Results indicate that the pendant alkyne on catalyst A coordinated with ruthenium hinders the hydration reaction due to unfavored ligand exchange with substrates. In contrast, catalyst B without a pendant group can catalyze the hydration of alkynes. However, catalyst B fails to further hydrogenate the aldehyde product into an alcohol, due to the lack of a bifunctional type of catalysis. With a pendant amine substituent on N,N-bidentate ligands, catalysts C and D can catalyze both the hydration of the alkyne and the hydrogenation of the aldehyde into an alcohol. The terminal amine ligand is advantageous to both the ligand exchange step and the bifunctional hydrogenation step. Our studies unfold the unique outer-sphere vinylidene mechanism for the Ru-catalyzed reductive hydration of terminal alkynes, which well explains the observed anti-Markovnikov hydration in experiments. These mechanistic insights should provide useful guidelines for the rational design of more efficient chemoselective single-catalyst systems for multiple catalytic processes.

Frustrated Lewis pairs (FLPs) emerge as a new type of bifunctional metal-free catalysts for reversible H2 activation, which is important for the storage and liberation of H2 or further controllable utilizing chemical fuels via hydrogenation/dehydrogenation. Herein, a DFT study was conducted to understand the geometric factors and electronic effects of FLPs on reversible H2 activation. The Lewis base group mainly contributes to the proton attachment, and influences the kinetics of the H2 activation. The Lewis acid group mainly relates to the hydride attachment, and affects more significantly on the thermodynamics of H2 activation. The dimer and quenched structure of FLPs also have a degree of influence on the performance of catalyzed H2 activation. A series of FLPs with para-substituted phenyl derivatives as LA groups were designed and evaluated. The results indicate that the variation of LA groups has significant impact on thermodynamic energy of dihydrogen adducts but insignificant effect on kinetics. Moreover, we found the thermodynamic energy of products has a good linear relationship with Hammett substituent constants. The solvent effect on H2 activation was also studied, and polar solvent is beneficial for zwitterionic products. These results should provide deeper insight to understand the relation between FLPs structure and reactivity, which is critical for rational design of more efficient FLPs catalysts for reversible H2 activation.

Lithium carbenoids are important reagents in organic synthesis. Systemic DFT calculations have been carried out to reveal the influence of hetero-aggregation states on the reactivity of lithium carbenoid reagents. The results indicate that the cyclopropanation reaction could be accelerated dramatically by hetero-aggregated lithium carbenoids with a halogen or oxygen as an α-heteroatom. The origin of the enhancement could attribute to the novel structural character of the hetero-aggregated lithium carbenoids. These intriguing finding predicts that it is practical to control a wide range of SN2-type organometallic reactions by using aggregated lithium carbenoids with other economical and convenient compounds.

An unusual cobalt(III)-catalyzed cross-coupling/cyclization of aryl C-H bonds of N-nitrosoanilines with alpha-diazo-beta-ketoesters has been achieved. This protocol features a unique combination of Csp2-H activation/Wolff rearrangement process, allowing for the rapid assembly of quaternary 2-oxindoles. The empirical evidence and density functional theory (DFT) calculations reveal the trapping process of transient acceptor ketene intermediates by cobalt metallocycles.

Metal hydrides play important roles in catalysis for sustainable energy, the environment, the petrochemical industry, and many important chemical processes. Despite this significance, the mystery behind metal hydride reactivity still remains. This theoretical study reveals a surprising reactivity discrepancy for different types of terminal hydrides and bridging hydrides, with Lewis acid–transition metal (LA–TM) hydride complex promoted alkene hydrogenations as model reactions, using density functional theory (DFT) studies. PBP(μ-H)CoH and DPB(μ-H)NiH complexes were chosen as representative models for the boryl type and the borane type LA–TM hydride, respectively. The bridging hydride is less reactive than the terminal hydride in the borane type complex DPB(μ-H)NiH. However, in sharp contrast, the bridging hydride is more reactive than the terminal hydride in the boryl type complex PBP(μ-H)CoH. Typical features of the electronic structure are unfolded to rationalize the origin of the reactivity discrepancy. The bridging hydride in the sp3 borane type DPB(μ-H)NiH complex forms a typical three-center two-electron (3c–2e) B–H–Ni bond. In the sp2 boryl PBP(μ-H)CoH complex, the bridging hydride forms an unusual three-center four-electron (3c–4e) B–H–Co bond. The 3c–2e bridging hydride is stabilized by two LA sites, leading to a lower nucleophilicity than that of a normal 2c–2e terminal hydride. Meanwhile the 3c–4e bridging hydride shows a stronger free-hydride character, resulting in a higher nucleophilicity than that of a 2c–2e terminal hydride. A general hydride nucleophilic trend is proposed: 3c–4e bridging hydride > 2c–2e terminal hydride > 3c–2e bridging hydride. These fundamental aspects of metal hydride reactivity should be helpful for mechanistic understanding and catalyst/material design involving metal hydride complexes.

Catalytic dehydration and dehydrogenation reactions of ethanol have been investigated systematically using the ab initio quantum chemistry methods The catalysts include water, hydrogen peroxide, formic acid, phosphoric acid, hydrogen fluoride, ammonia, and ethanol itself. Moreover, a few clusters of water and ethanol were considered to simulate the catalytic mechanisms in supercritical water and supercritical ethanol. The barriers for both dehydration and dehydrogenation can be reduced significantly in the presence of the catalysts. It is revealed that the selectivity of the catalytic dehydration and dehydrogenation depends on the acidity and basicity of the catalysts and the sizes of the clusters. The acidic catalyst prefers dehydration while the basic catalysts tend to promote dehydrogenation more effectively. The calculated water-dimer catalysis mechanism supports the experimental results of the selective oxidation of ethanol in the supercritical water. It is suggested that the solvent- and catalyst-free self-oxidation of the supercritical ethanol could be an important mechanism for the selective dehydrogenation of ethanol on the theoretical point of view.

The mechanism of the reaction of Methylidyne Radical (CH) with acetaldehyde (CH 3 CHO) has been investigated using CBS-QB3//B3LYP/aug-cc-pVTZ method. The initial CH + CH 3 CHO reaction is a barrierless process, forming a linear intermediate, CH 3 CHOCH, which can be converted into several products. The microscopic mechanism recommended by the present study not only identifies the products observed by previous experimental studies but also explains the isotopic effects (CH/CCD) observed experimentally. In view of the calculated energies, C 2 H 5 + CO is the most exothermic product pair, additionally, the energy barrier of this product channel is the lowest. Concerning the hydrogen elimination channel, acrolein (CH 2 CHCHO) and methylketene (CH 3 CHCO) are preferable co-products. Furthermore, a new product channel, C 2 H 3 + CH 2 O, has been discovered.

The mechanism and kinetics for the O( 3 P) + CH 3 CH CHCN reaction has been investigated firstly. The BHandHLYP and M05-2X methods were employed to obtain the initial geometries. The triplet/singlet potential energy surfaces (PESs) were constructed with high-level BMC-CCSD method. The conventional transition-state theory (CTST) and multichannel RRKM theory were employed to calculate the total and individual rate constants over a wide range of temperatures under high-pressure limit. Our computed rates agree well with the available experimental results. The yield of IM1 is 0.9–0.5 from 200 to 1000 K, and the construction of h-P1(OH + CH 2 CHCHCN) is 0.42 at 2000 K under high-pressure limit. The yields of the predicted decomposition products P1(CH 3 + HCOHCCN), P2(HCCN + CH 3 CHO) and P3(H + CH 3 COHCCN) at 298 K and 1 atom are 0.81, 0.07, and 0.09, respectively.

Lewis acid–transition metal (LA–TM) complexes have been emerging as a novel type of bifunctional catalyst for H2 activation. The crucial role of the auxiliary ligand in the mechanism and reactivity of H2 activation were theoretically studied with (tris(phosphino)borane)Fe(L) (L = N2, CNtBu, and CO) as model LA–TM complexes. The axial auxiliary ligand is found to play an important role in the complex electronic structures, via significantly tuning the energy levels of dxz, dyz, and of the Fe–B bond. We systematically evaluated both the ligand dissociative mechanism and the associative mechanism with the binding auxiliary ligand. In the ligand dissociative mechanism, the reaction starts with the dissociation of the axial ligand. Then, H2 coordinates to the iron center either at the axial position or on the equatorial plane. The axial coordinated H2 cleaves via oxidative addition to a metastable octahedral dihydride intermediate, which further isomerizes to a more stable five-coordinated trigonal bipyramidal intermediate with a bridging hydride stabilized by the iron center and the Lewis center, boron. On the other hand, the equatorial coordinated H2 is cleaved by the cooperation of the Fe–B bond, directly to the trigonal bipyramidal dihydride intermediate. In comparison, in the ligand associative mechanism, the H2 molecule splits up upon approaching the iron center via an octahedral transition state, with the auxiliary ligand remaining at the axial position. Our results suggest that the triplet state axial reaction pathway of the L-dissociative mechanism is the most favorable one for H2 activation. The isomerization of hydride instead of H2 cleavage may be the rate-determining step. H2 activation occurs homolytically on the metal center without LA assistance, which is significantly different from other tetradentate LA–TM systems that activate H2 in a synergetic heterolytic mode. The obtained tendency of the dissociation free energies for (tris(phosphino)borane)Fe(L) (L = N2, CNtBu, and CO) (2.3, 8.1, and 15.7 kcal mol−1, respectively) and the activation free energies of the rate-determining step (20.3, 26.0, and 33.7 kcal mol−1, respectively) explains well their activity trend. The extraordinary effect of the auxiliary ligand on the mechanism and reactivity should provide new information for future development of LA–TM bifunctional catalysts.

In this work, using quantum chemistry methods the reactions of Hg and HgO with six organics including methane (CH4), benzene (C6H6), methanol (CH3OH), formaldehyde (HCHO), formic acid (HCOOH) and phenol (C6H5OH) in sludge incineration were investigated. The computational result indicates that Hg reacts with six organics via insertion mechanism to form CH3HgH, CH3OHgH, CH3HgOH, HHgCH2OH, HCOHgH, H2CHgO, HHgCOOH, HOCHHgO, HCOOHgH, HCOHgOH, C6H5HgH, C6H5OHgH, C6H5HgOH, and m-, o-, p-HHgC6H4OH. However, all barriers involved are extremely high and all products are rather unstable, therefore, Hg will be discharged as elements into fuel gas. With extra oxygen supplied Hg could be oxidized to HgO firstly; subsequently, CH3OHgOH, HCOHgOH, HOCOHgOH, C6H5HgOH and o-HOHgC6H4-OH were formed when HgO reacts with above above organics. The corresponding barriers are lower and all products are much more stable, indicating these Hg-contained organic compounds would be generated readily in incineration of sludge. Therefore it is presumed that in presence of oxygen Hg is more active to react with organics in sludge incineration.

The hydroxyl radical, as the most important oxidant, controls the removal of some volatile organic compounds (VOCs) in the atmosphere. In this work, the atmospheric oxidation processes of acrylic acid by OH radical have been investigated by density functional theory (DFT). The energetic routes of the reaction of CH2CHCOOH with OH radical have been calculated accurately at the CCSD(T)/cc-pVTZ//M06-2X/6-311++G(d,p) level. It is implicated that the oxidation has five elementary reaction pathways mostly hinging on how hydroxyl radical approaches to the carbon skeleton of acrylic acid. The atmospheric degradation mechanisms of the CH2CHCOOH by OH radical are the formation of reactive intermediates IM1 and IM2. Meanwhile, the further oxidation mechanisms of IM1 and IM2 by O3 and NO are also investigated. The rate coefficients have been computed using tight transition state theory of the variflex code. The calculated rate coefficient is 2.3 × 10−11 cm3 molecule−1 s−1 at standard pressure and 298 K, which is very close to the laboratory data (1.75 ± 0.47 × 10−11 cm3 molecule−1 s−1). Moreover, the atmospheric lifetime of acrylic acid is about 6 h at 298 K and 1 atm, implying that the fast sinks of acrylic acid by hydroxyl radical.

This study presents new mechanistic insights into the frustrated Lewis pairs (FLPs) catalyzed C–H activation of heteroarenes. Besides the generally accepted concerted C–H activation, a novel stepwise carbene type pathway is proposed as an alternative mechanism. The reaction mechanisms can be varied by tuning the distance between Lewis acid and Lewis base due to catalyst–substrate match. These results should expand the understanding of the structure and function of FLPs for catalyzed C–H activation.