Abel Idrice Adjieufack

The prolonged heating of an N -heterocyclic carbene-stabilised borenium cation resulted in the abstraction of a –C ₆ F ₅ group from its B(C ₆ F ₅ ) ₄ ⁻ counter-anion.

Using the framework of the bonding evolution theory (BET), we investigated the molecular mechanism of the [3+2] cycloaddition reaction of benzonitrile oxide (1) with five ethylenic derivatives (2a–e). The global mechanism consists in the concerted attack of one of the O lone pairs of 1 on one of the atoms of the C–X double or triple bond of 2 (X = C, O, N), the attack of the C–X double or triple bond of 2 on the C of the C–N triple bond of 1, and the conversion of C–N triple bond of 1 into a double bond and the creation of a lone pair on N. The reaction proceeds through a one‐step mechanism, the creation and modification of the electron basins occur at different places along the intrinsic reaction coordinate, as unraveled by the BET study. In the cases of dipolarophiles (2a–c), first the C–N triple bond of 1 is converted into a double bond with the creation of a lone pair on N. Then, a C–C single bond between the C–N triple bond of 1 and one of the C atoms of the C–C double or triple bond of 2 is created. Finally, the O–C single bond is formed. Concerning 2e, the meta‐path follows the same reaction mechanism as 2a–c, while for the ortho‐path, the formation of C–N and C–O bonds are synchronous and mediated by the N4 lone pair. A similar observation (but for the two C–O bonds) is found for 2d ortho‐path while the mechanism for the meta‐path is quite different to the other ones due to the formation of an O–O bond. The present work represents a new example showing how the use of BET can provide curly arrows and electron flow representation to unravel molecular mechanisms.

The [4+2] Diels‐Alder cycloaddition reaction between 2,5‐DMF (1) and ethylene derivatives (2 a‐h) activated by electron‐withdrawing groups has been studied at the density functional theory level using a panoply of tools to unravel the reaction mechanisms. From the analysis of the reactivity indices, 2 a‐h behave as electrophiles while 1 as nucleophile, and the activation of the double bond of ethylene increases its electrophilicity, which is accompanied by an enhancement of the polarity of the reaction. The activation Gibbs free energy decreases linearly as a function of this increase of polarity, as estimated by the electrophilicity difference between the reactants. The difference of electrophilicity drives also the global electron density transfer at the transition state and the asynchronicity of the reaction, as evaluated by the difference of carbon‐carbon bond lengths in the transition state. Then, Bonding Evolution Theory shows that the activation of the double bond of ethylene by an electron‐withdrawing group changes the reaction mechanism from a one‐step synchronous process to a one‐step asynchronous process. Generally, the endo pathway is kinetically favored but, thermodynamically, it is the exo pathway. Finally, using the Distortion/Interaction‐Activation Strain, it is shown that the endo/exo selectivity is mostly driven by the differences of interaction energies.

In this paper, we have explored the influence of alkylene‐bridged length and coordination mode on the reactivity of a series of 24 alkylene‐bridged palladium complexes using computational tools (B3PW91/LANL2DZ//6‐31G(d) level) in gas phase and DMSO. These palladium complexes prefer a boat and chair configuration for methylene and ethylene bridge length, respectively. In addition, phenyl and nitro complexes present a higher activation for Pd—C bonds while the most stable Pd⋯C interactions are observed for abnormal mode with methylene bridge. According to the energy decomposition analysis (EDA), hydrogen and phenyl complexes in both chelation modes present a better electrostatic character. Moreover, Pd⋯C interactions are stronger compared to the Pd⋯X ones for ethylene‐bridged abnormal complexes (in gas phase). Finally, the donation/back‐donation ratio (d/b) values reveal the Fischer carbene character of these [bis(NHC)]⋯[PdX₂] interactions. Concerning the hybridization around the metal cation for the Pd—C bond, the sp²d type is observed for methylene‐bridged palladium complexes while the sp³ one is observed for ethylene bridge complexes.

We have explored the chelation of dimethylglyoxime ligand to divalent (nd^x: x = 6, 7, 8) transition metal (TM) cations in two media (gas phase and water) at the B3LYP//LANL2DZ/6–311+G (d,p) and B3LYP/def2‐TZVP level at lower multiplicity and higher multiplicity states. Majority of the 18 optimized halide (chloride and bromide) complexes prefer square planar configuration. The correlations discerned between the experimental structural data and their estimated counterparts demonstrate a good credibility for complexes at lower multiplicity state. The basis set superposition errors (BSSEs) estimated is very small which reflects the fact that the choice of different basis sets (B3LYP//LANL2DZ/6–311+G (d,p)) introduces a slight bias in the calculation of energies. The ADMP (atom‐centered density matrix propagation) simulations in water on chloride complexes indicate the irreversible nature of these M—N dissociation in trajectory simulation process. This fact explains our exclusive focus on the examination of the [glyoxime ligand]…[MX₂] interactions. In addition, the solvation of (3d and 4d) transition metal chloride complexes causes a sensitive augmentation of the metal ion affinity (MIA) with an average of 0.29 and 0.24 kcal/mol. In both multiplicity states, the topological parameters have illustrated that the M—N and M—X bonds are typical metal–ligand in both media. The average ΔE_orb/ΔE_steric ratio equal to 0.45 and 0.11 in gas phase and water, respectively, reveals the predominance of the contributions from non‐covalent bonding interactions (NCI) compared to those of covalent bonding. But, the maximal value equal to 6.760 is obtained for bromide rhodium complex in water. NBO analysis in both media highlights the fact that a more pronounced ionic character is observed for the majority of the chloride complexes at both spin multiplicity states because of their higher retained charges on the metal atom. For [dimethylglyoxime]…[MX₂] interaction (X = Cl and Br), the charge decomposition analysis demonstrates that the lowest value of the d/b ratio is found for the chloride platinum complex at lower multiplicity state in water. This is a proof of its strong relativistic effects.

Bis-N-heterocyclic carbene ligands (bis(NHC)) have introduced a new approach to designing homogeneous and heterogeneous catalysts, demonstrating the versatility of ligand concepts in catalysis. This study presents a computational analysis of palladium (+II and +IV) complexes containing either a normally (bis(nNHC)) or an abnormally (bis(aNHC)) bound CH₂-bridged bis-N-heterocyclic carbene ligand; in addition, ancillary ligands are permuted from chlorides (X = Cl) to bromides (X = Br). Density functional theory at the B3PW91/6-31G(d)/Lanl2DZ level in the gas phase was used to investigate the electronic structure and bonding properties of bis(NHC)Pd^IIX₂ and bis(NHC)Pd^IVX₄ for bis(NHC) palladium(II) dihalide and palladium(IV) tetrachloride complexes, respectively. Results indicate that all of the palladium complex structures prefer a flexible boat-type conformation with an average C_2v symmetry, according to bond property (C_carbene–Pd and Pd–Cl[Br]) analysis. The strength of these bonds depends on coordinating halide ions (Cl⁻ and Br⁻), the type of ligand (bis(nNHC) and bis(aNHC)), and the palladium oxidation state (+II and +IV). Analysis of thermodynamic parameters (ΔH⁰, ΔG⁰, and ΔE_bind) shows an increase in values from an abnormal to normal chelating mode in tetrahalides, whereas the opposite is observed for dihalide complexes. The lower π-backbonding ability of the metal, which is influenced by the quantity and size of halide ions involved, could be one possible explanation for this deficiency.

In this study, monobrominated coumarins (5-6) and bis-coumarins (7-9) were synthesized from 3-carboxylic coumarin and 7-hydroxy-4-methyl coumarin using 1,4-dibromobutane as a binding agent, according to the synthesis procedures described in the literature. Amongst these coumarins, three are new compounds: monobrominated coumarin 5 and bis-coumarins 7 and 9. The structures of the synthesized coumarins were confirmed by FTIR, NMR and HRMS-ESI. In vitro antimicrobial evaluation of these coumarins against strains of twelve bacteria and four fungi revealed their bactericidal and fungicidal properties, with increased antibacterial activity for monocoumarins and improved antifungal activity for bis-coumarins. It was also found that the antibacterial activity was enhanced by the etheric bond, Br atom and alkyl chain and reduced by the ester bonds at position 3 of the pyrone ring or an additional coumarin unit, while the antifungal activity was reinforced by ester bonds and deactivated by the Br atom. For the first time, the in silico investigations of such coumarins were carried out and it was observed that they are less toxic, suitable for oral administration with good permeability through cell membrane, are able to circulate freely in the bloodstream and cross Blood-Brain-Barriers. Moreover, their molecular docking in DNA indicated stable coumarin-DNA complexes with good scores. The results of molecular dynamics simulations performed for 200 ns revealed the rigidity and stability of bis-coumarins (7-9) in the DNA binding pocket and predict that they are potent binders. Communicated by Ramaswamy H. Sarma

In the present work, the bond breaking/forming events along the intramolecular Diels–Alder (IMDA) reaction of (2E,4Z,6Z)-2(allyloxy)cycloocta-2,4,6-trien-1-one have been revealed within bonding evolution theory (BET) at the density functional theory level, using the M05-2X functional with the cc-pVTZ basis set. Prior to achieving this task, the energy profiles and stationary points at the potential energy surface (PES) have been characterized. The analysis of the results finds that this rearrangement can proceed along three alternative reaction pathways (a–c). Paths a and b involve two steps, while path c is a one-step process. The first step in path b is kinetically favored, and leads to the formation of an intermediate step, Int-b. Further evolution from Int-b leads mainly to 3-b1. However, 2 is the thermodynamically preferred product and is obtained at high temperatures, in agreement with the experimental observations. Regarding the BET analysis along path b, the breaking/forming process is described by four structural stability domains (SSDs) during the first step, which can be summarized as follows: (1) the breaking of the C–O bond with the transfer of its population to the lone pair (V(O)), (2) the reorganization of the electron density with the creation of two V(C) basins, and (3) the formation of a new C–C single bond via the merger of the two previous V(C) basins. Finally, the conversion of Int-b (via TS2-b1) occurs via the reorganization of the electron density during the first stage (the creation of different pseudoradical centers on the carbon atoms as a result of the depopulation of the C–C double bond involved in the formation of new single bonds), while the last stage corresponds to the non-concerted formation of the two new C–C bonds via the disappearance of the population of the four pseudoradical centers formed in the previous stage. On the other hand, along path a, the first step displays three SSDs, associated with the depopulation of the V(C2,C3) and V(C6,C7) basins, the appearance of the new monosynaptic basins V(C2) and V(C7), and finally the merging of these new monosynaptic basins through the creation of the C2–C7 single bond. The second step is described by a series of five SSDs, that account for the reorganization of the electron density within Int-a via the creation of four pseudoradical centers on the C12, C13, C3 and C6 carbon atoms. The last two SSDs deal with the formation of two C-C bonds via the merging of the monosynaptic basins formed in the previous domains.

Bonding evolution theory has been used at the density functional theory level [ωB97X-D exchange-correlation functional, 6-311G(d,p) basis set, and solvent (toluene) effects with polarizable continuum model] to unravel the reaction mechanism of the intramolecular aza-Wittig reaction of 2-(acetylthio)phenyl isocyanate (1) catalyzed by 3-methyl-1-phenyl-2-phospholene 1-oxide (2) to form 2-methylbenzothiazole (3). The reaction involves four steps (transition states) corresponding to (1) the formation of a cycloadduct (O–C then P–N bonds), (2) a decarboxylation leading to the formation of an iminophosphorane, and (3) an intramolecular [2+2] cycloaddition (N–C then P–O bonds) followed by (4) a retro [2+2] cycloaddition (cleavage of the P–N then O–C bonds) to get the product and regenerate the catalyst. Step 1 is the rate-determining step with an activation Gibbs free enthalpy of 21 kcal mol–1 and it is favored with respect to a competitive pathway leading to the formation of another cycloadduct (P–C then O–N bonds). The whole reaction is exergonic with a Gibbs free energy decrease of 31 kcal mol–1, associated with the liberation of a CO2 molecule and the formation of the aromatic benzothiazole. Following the scale of Domingo, the successive steps of the reaction have a polar nature.