Chem4Energy: a consortium of the Royal Society Africa Capacity-Building Initiative.

The Africa Capacity-Building Initiative is a Royal Society programme funded by the former UK Department for International Development to develop collaborative research between scientists in sub-Saharan Africa and the UK. Initially, four institutions were involved in the Chem4Energy consortium: Cardiff University in the UK and three African partners, the Kwame Nkrumah University of Science and Technology, Ghana, the University of Namibia and the University of Botswana, soon also including the Botswana International University of Science and Technology. The Chem4Energy research programme focused on 'New materials for a sustainable energy future: linking computation with experiment', aiming to deploy the synergy between state-of-the-art computational and experimental techniques to design and optimize new catalysts and semiconductor materials for renewable energy applications, based on materials that are abundant and readily available in African countries.

Exploring the peri- and stereo- selectivities of the cycloaddition reaction of 2-(2- dimethylaminovinyl)-1-benzopyran-4-one with N-phenylmaleimide (NPM) and dimethylacetylenedicarboxylate (DMAD) - A DFT study.

The [4 + 2] cycloaddition reactions of 2-styrylchromones have been predominantly described as one of the efficient methods for the synthesis of xanthones-a prominent class of tricyclic molecules that occur widely in nature. These xanthones are well known for their pharmacological activities especially their role as anti-cancer agents in the medicinal world. In this study, the mechanistic insight into the unusual (peri- and stereo-) selectivities of the reaction of 2-(2-dimethylaminovinyl)-1-benzopyran-4-one (A1) with N-phenylmaleimide (NPM) and dimethylacetylenedicarboxylate (DMAD) has been studied using density functional theory (DFT) at the M06-2X/6-311G (d, p) level of theory.

The catalytic hydrogenolysis of compounds derived from guaiacol on the Cu (111) surface: mechanisms from DFT studies.

Pyrolysis oils have inferior properties compared to liquid hydrocarbon fuels, owing to the presence of oxygenated compounds such as guaiacol, CH(OH)(OCH). The catalytic hydro-deoxygenation (HDO) of phenolic compounds derived from guaiacol, catechol, phenol and anisole were investigated over the Cu (111) surface to unravel the elementary steps involved in the process of bio-oil upgrade. The phenolic compounds adsorb through their π systems to the surface, where steric effects of the methoxy group reduce the stability of anisole on the surface.

A quantum mechanistic insight into the chemo- and regio-selective [3 + 2]-cycloaddition reaction of aryl hetaryl thioketones with diazoalkanes and nitrile oxide derivatives.

In this quantum mechanistic study, density functional theory computations at the B3LYP hybrid level of theory, in addition to triple zeta basis set 6-311G (d, p), were utilized to investigate the chemoselectivities and regioselectivities of the [3 + 2] cycloaddition reaction of phenyl (2-thienyl) thioketone (B1) derivatives with nitrile oxide (B2) and diazopropane derivatives (B3). From the computations obtained, the reactions of nitrile oxide and diazopropane derivatives with phenyl (2-thienyl) thioketone proceed through an asynchronous one-step mechanism. The initial [3 + 2] cycloaddition reaction of B1 and B3 is followed by a nitrogen extrusion which is also highly asynchronous.

Quantum Mechanical Elucidation on [3+2] cycloaddition reaction of aryl nitrile oxide with cyclopentenones.

The [3 + 2] cycloaddition (32CA) reaction of benzonitrile oxide (BNO) with 4-substituted 4-hydroxy-2-cyclopentenone has been investigated using molecular electron density theory (MEDT) at the Density Functional Theory (DFT) B3LYP/6-31G (d), M06/6-311G (d,p) and M06-2X/6-311++G (d,p) levels. The present theoretical computations indicate that the reaction of BNO with 4-substituted 4-hydroxy-2-cyclopentenones is via [3 + 2] cycloaddition, where the three atom component (TAC) chemo-selectively adds across the alkene functionality in the 2-cyclopentenones (Path A). Analysis of the electrophilic P and nucleophilic P Parr functions at the different reaction sites in the alkene counterpart indicates that the aryl nitrile oxides add across the atomic centers with the highest Mulliken atomic spin densities.

A DFT Mechanistic Study on Base-Catalyzed Cleavage of the -O-4 Ether Linkage in Lignin: Implications for Selective Lignin Depolymerization.

The detailed mechanism of the base-catalyzed C-C and C-O bond cleavage of a model compound representing the -O-4 linkage in lignin is elucidated using DFT calculations at the M06/6-31G* level of theory. Two types of this linkage have been studied, a C2 type which contains no -carbinol group and a C3 type which contains a -carbinol. Cleavage of the C2 substrate is seen to proceed a 6-membered transition structure involving the cation of the base, the hydroxide ion and the α-carbon adjacent to the ether bond.

Does the reaction of nitrone derivatives with allenoates proceed by an initial (3 + 2) cycloaddition or O-Nucleophilic addition? A quantum chemical investigation.

The question of whether the reaction between nitrone derivatives and allenoates proceeds with initial (3 + 2) cycloaddition (32CA) or the oxygen-nucleophilic (O-nucleophilic) addition has been theoretically investigated using density functional theory (DFT) at the M06-2X/6-311G(d,p) level of theory. In all of the reactions considered, the initial 32CA route is kinetically and thermodynamically preferred over the initial O-nucleophilic addition. Increasing the steric bulk of the substituents on the reactants bridges the kinetic and thermodynamic gap between the initial 32CA and O-nucleophilic addition but the 32CA is still energetically preferred, showing that with increasing steric bulk, the O-nucleophilic addition may become competitive with the 32CA route.

A DFT study of the double (3 + 2) cycloaddition of nitrile oxides and allenoates for the formation of spirobiisoxazolines.

The molecular mechanism of the double (3 + 2) cycloaddition (32CA) reaction between nitrile oxides and allenoates has been studied using density functional theory at the M06-2X/6-311G (d,p) level of theory. In the first 32CA, the nitrile oxide adds chemo- and regio-selectively to the C-C double bond of the allenoate closest to the carboxylate group followed by a subsequent regioselective addition to the olefinic bond of the isoxazoline intermediate. The rate constant for the preferred pathway (formation of 4-methylene-2-isoxazoline intermediate) in the reaction of ethyl substituted allenoate and mesitonitrile oxide is 5.

Exploring the chemo-, regio-, and stereoselectivities of the (3 + 2) cycloaddition reaction of 5,5-dimethyl-3-methylene-2-pyrrolidinone with C,N-diarylnitrones and nitrile oxide derivatives: a DFT study.

The (3 + 2) cycloaddition (32CA) reaction is an efficient method for the synthesis of many biologically active heterocyclic compounds, but there are several regio- and stereochemical issues that must be fully understood to exploit the full utility of its synthetic power. We herein explored the chemo-, regio-, and stereoselectivities of the 32CA reaction of 5,5-dimethyl-3-methylene-2-pyrrolidinone (B1) to C,N-diarylnitrones (B2), and nitrile oxide derivatives (B3) with DFT at the M06/6-311G(d,p) level of theory. The reactions occur via an asynchronous one-step mechanism, with the chemoselective addition of the C,N-diarylnitrones, and nitrile oxide derivatives across the olefinic bond of 5,5-dimethyl-3-methylene-2-pyrrolidinone being the most preferred kinetically and thermodynamically.

A DFT mechanistic study on oxidative dehydrogenative Diels-Alder reaction of alkylbenzenes.

Cross-dehydrogenative Diels-Alder cycloaddition reaction between readily-available alkyl benzenes and electron-deficient dienophiles is an attractive synthetic route to access carbocyclic compounds which have high utility in the chemical and pharmaceutical industries. This work reports a study at the M06-2X/6-311G(d) and M06-2X/6-311++G(d,p) levels of theory on the reaction of alkyl benzenes with electron-deficient dienophiles in the presence of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an oxidant and hydroquinone as an activator, so as to understand the chemoselectivity of the reaction (addition across the alkene functionality versus the ketone functionality), the role of the activator, the effects of substituents and the effect of solvent on the reaction. The results show the addition of the alkene bonds of methylstyrene across the alkene functionality of the electron-deficient dienophiles has generally low barriers compared to the addition across the carbonyl functionality of the electron-deficient dienophile.

Computational study on the mechanism of the reaction of benzenesulfonyl azides with oxabicyclic alkenes.

The reaction of benzenesulfonyl azides with oxabicyclic alkenes to form aziridines could either proceed via initial [3 + 2] cycloaddition to form triazoline intermediates which then leads to aziridines, or via initial dinitrogen cleavage of the benzenesulfonyl azide to afford a nitrene intermediate followed by addition of this nitrene species across the olefinic C-C bond of the oxabicyclic alkene. Calculations at the DFT M06-2X/6-311G(d,p) level indicate that the initial [3 + 2] cycloaddition reaction of benzenesulfonyl azide and oxabicyclic alkene has barriers of 15.0 kcal/mol (endo) and 10.

(3 + 2) cycloaddition reaction of 7-isopropylidenebenzonorbornadiene and diazomethane derivatives: A theoretical study.

The ability to synthesize targeted molecules hinges on detailed mechanistic insight of the reaction. The 1,3-dipolar cycloaddition reaction between diazomethane derivatives and 7-isopropylidenebenzonorbornadiene have been extensively studied using density functional theory (DFT) at the M06-2X/6-311G(d,p) level of theory in order to delineate the peri-, regio-, and stereo-selectivities of the reaction. The diazomethane is shown to periselectively add across the endocyclic olefinic bond of the 7-isopropylidenebenzonorbornadiene and stereoselectively in the exo fashion, yielding the exo-cycloadduct as the major product, with a rate constant of 3.

Investigating the regio-, stereo-, and enantio-selectivities of the 1,3-dipolar cycloaddition reaction of C-cyclopropyl-N-phenylnitrone derivatives and benzylidenecyclopropane derivatives: A DFT study.

The biomedical importance of spirocyclopropane isoxazolidine derivatives is widely known. The 1,3-dipolar cycloaddition (1,3-DC) of C-cyclopropyl-N-phenylnitrone derivative and benzylidenecyclopropane derivatives leading to the formation of 5- and 4-spirocyclopropane isoxazolidines derivatives have been studied using density functional theory (DFT) at M06-2X/6-311G (d,p) level of theory. An extensive exploration of the potential energy surface shows that the 1,3-dipole adds across the dipolarophile via an asynchronous concerted mechanism.

Permanganyl chloride-mediated oxidation of tetramethylethylene: A density functional theory study.

The mechanisms of the oxidation of tetramethylethylene (TME) by permanganyl chloride (MnOCl) have been explored on the singlet and triplet potential energy surfaces at the B3LYP LANL2DZ/6-31G (d) level of theory. The results show that the pathway leading to the formation of the five-membered dioxylate through concerted [3 + 2] addition is favored kinetically and thermodynamically over the three other possible pathways, namely the [2 + 2] addition via the transient metallaoxetane intermediate, epoxidation, and hydrogen transfer pathways. The epoxide precursor that on hydrolysis would yield the epoxide product will most likely arise from a stepwise path through the intermediacy of an organometallic intermediate.

Peri-, Chemo-, Regio-, Stereo- and Enantio-Selectivities of 1,3-dipolar cycloaddition reaction of C,N-Disubstituted nitrones with disubstituted 4-methylene-1,3-oxazol-5(4H)- one: A quantum mechanical study.

The peri-, chemo-, regio-, stereo- and enantio-selectivities of 1,3-dipolar cycloaddition reaction of C,N-disubstituted nitrones with disubstituted 4-methylene-1,3-oxazol-5(4H)-one have been studied using density functional theory (DFT) at the M06-2X/6-311G (d,p) level of theory. The 1,3-dipole preferentially adds chemo-selectively across the olefinic bond in a (3 + 2) fashion forming the corresponding spirocycloadduct. The titled reaction occurs with poor enantio- and stereo-selectivities, but a high degree of regio-selectivity is observed for the addition of the 1,3-dipole across the dipolarophile.

DFT mechanistic studies on the regio-, stereo-, and enantio-selectivity of 1,3 dipolar cycloadditions of quinolinium imides with olefins, maleimides, and benzynes for the synthesis of fused N,N'-heterocycles.

This work investigated computationally the regio-, stereo-, and enantio-selectivity of the reactions of azomethine imines with olefins, maleimides, and benzynes, important reactions towards the synthesis of heteropolycyclic, N,N'-fused, spirocyclic systems, which serve as building blocks for the synthesis of many pharmaceuticals, agrochemicals, and biologically active compounds. The results show that the thermally controlled diastereoselective [3 + 2] cycloaddition reaction between quinolinium imide and methyl acrylate provides two regio-isomers: 1,4-regioisomer (N-C1, C-C2) and 1,3-regioisomer (N-C2, C-C1). The 1,4-regioisomer has cis and trans-stereoisomers while the 1,3-regioisomer has R-enantiomer and S-enantiomer, and the barriers for the formation of these isomers are 5.

The mechanisms of gallium-catalysed skeletal rearrangement of 1,6-enynes - Insights from quantum mechanical computations.

The transition metal-catalysed skeletal reorganization of 1,6-enynes can lead to three types of products - a type I product occurring via the cleavage of the alkene C-C bonds and the migration of the terminal alkene carbon to the terminus of the alkyne; a type II product arising from cleavage of both the double and the triple bonds followed by insertion of the terminal alkene carbon into the alkyne C-C triple bond; and a type III product which is obtained when there is a cleavage of the olefinic bond followed by formation of two new bonds from each carbon to each of the acetylenic carbons. The course of these reactions is highly dependent on the metal catalyst used and type of substitution at the alkene and alkyne moieties of the enyne. In this mechanistic study of the re-organization of 1,6-enynes catalysed by GaCl, performed at the DFT M06/6-311G(d,p) level of theory, the parent reaction selectively leads to the formation of the type I product through the formation of the open cyclopropane ring.

Mechanistic studies on tandem cascade [4 + 2]/ [3 + 2] cycloaddition of 1,3,4-oxadiazoles with olefins.

The mechanism of the reaction of 1,3,4-oxadiazoles with alkenes (ethylene) and cycloalkenes (cyclobutene, cyclopentene, cyclohexene and cycloocene) have been studied computationally at the DFT M06-2X/6-311G* level. The reaction is found to proceed via a concerted [4 + 2] addition followed by nitrogen extrusion and then [3 + 2] addition in a tandem cascade fashion, which in the case of cycloalkenes leads to exo-fused or endo-fused subframes, the exo of which is kinetically and thermodynamically favored. The [4 + 2] step is the rate-determining step of the reaction.

1, 3-Dipolar cycloaddition reactions of selected 1,3-dipoles with 7-isopropylidenenorbornadiene and follow-up thermolytic cleavage: A computational study.

The mechanism, regio-, stereo-, and enantio-selectivities of the 1,3-dipolar cycloaddition reactions of 7-isopropylidenenorbornadiene (DENBD) with nitrones and azides to form pharmaceutically relevant isoxazolidine and triazole analogues have been studied computationally at the M06/6-31G(d), 6-31G(d,p), 6-311G(d,p), 6-311++G(d,p) and M06-2X/6-31G(d) levels of theory. In the reactions of DENBD with phenyl nitrones, the cycloaddition steps have low activation barriers, with the highest being 16 kcal/mol; and the Diels-Alder cycloreversion steps have generally high barriers, with the lowest being 20 kcal/mol, suggesting that the isolable products in these reactions are the bicyclic isoxazolidine cycloadducts and not the thermolytic products. This is in contrast to the reactions of DENBD with phenyl azide where the isolable products are predicted to be the thermolytic products since the Diels-Alder cycloreversion steps had relatively lower activation barriers.

Quantum chemical studies on the mechanistic aspects of tandem sequential cycloaddition reactions of cyclooctatetraene with ester and nitrones.

The mechanisms of the tandem sequential [4 + 2]/[3 + 2] and [3 + 2]/[4 + 2] cycloaddition sequences involving an ester, cyclooctatetraene (COTE), and cyclic and acyclic nitrones for the formation of a diverse range of isoxazolidine derivatives and other synthetic precursors are reported. A thorough exploration of the PES has characterized several regio-, stereo- and enantio-selective mechanistic channels involved in these reactions. A perturbation molecular orbital (PMO) analysis been employed to rationalize the results.

Computational studies on [4 + 2] / [3 + 2] tandem sequential cycloaddition reactions of functionalized acetylenes with cyclopentadiene and diazoalkane for the formation of norbornene pyrazolines.

The mechanistic pathways for the sequential tandem [4 + 2] / [3 + 2] versus [3 + 2] / [4 + 2] cycloaddition reaction of functionalized acetylenes with cyclopentadiene and dimethyl diazopropane for the formation of norbornene pyrazolines, employed in the synthesis of pharmaceutically relevant compounds, have been studied computationally with DFT at the M06-2X/6-31G(d) and M06-2X/6-31G(d,p) levels of theory. We have established that, in the reaction of the parent (unsubstituted) acetylene with cyclopentadiene and dimethyl diazopropane, the order of the tandem addition has no substantial effects in product outcomes. The same product is obtained provided the reaction components remain the same for both [4 + 2]/[3 + 2] and [3 + 2]/[4 + 2] tandem addition sequences.

Ab initio investigation of O adsorption on Ca-doped LaMnO cathodes in solid oxide fuel cells.

We present a Hubbard-corrected density functional theory (DFT+U) study of the adsorption and reduction reactions of oxygen on the pure and 25% Ca-doped LaMnO3 (LCM25) {100} and {110} surfaces. The effect of oxygen vacancies on the adsorption characteristics and energetics has also been investigated. Our results show that the O2 adsorption/reduction process occurs through the formation of superoxide and peroxide intermediates, with the Mn sites found to be generally more active than the La sites.

Water-soluble SNS cationic palladium(II) complexes and their Suzuki-Miyaura cross-coupling reactions in aqueous medium.

Unlike their SCS analogues, SNS pincer complexes are poorly studied for their use in coupling reactions. Accordingly, a series of water soluble cationic Pd(II) SNS pincer complexes have been successfully synthesised and investigated in detail for their catalytic activity in Suzuki-Miyaura coupling reactions. By using only 0.

Trapping of 1,2-cyclohexadiene: A DFT mechanistic study on the reaction of 1,2-cyclohexadiene with olefins and nitrones.

The mechanistic aspects of cycloaddition reactions of 1,2-cyclohexadiene with olefins and nitrones have been investigated with DFT calculations. The results show that the cycloaddition reactions of 1,2-cyclohexadiene with olefins do not go through a concerted pathway (one-step mechanism) but rather a stepwise one involving the formation of a biradical intermediate which then closes to form final cycloadduct. Electron-withdrawing substituents on the 1,2-cyclohexadiene decrease the activation barrier of the biradical-forming step but increase the barrier of the product-forming step and product stability, while electron-donating substituents on the 1,2-cyclohexadiene increase the barriers for both the biradical-forming step and the product-forming step but decrease the product stability.