Carboranes as Lewis Acids: Tetrel Bonding in CB11H11 Carbonium Ylide

High-level quantum-chemical computations (G4MP2) are carried out in the study of complexes featuring tetrel bonding between the carbon atom in the carbenoid CB11H11—obtained by hydride removal in the C-H bond of the known closo-monocarbadodecaborate anion CB11H12(−) and acting as Lewis acid (LA)—and Lewis bases (LB) of different type; the electron donor groups in the tetrel bond feature carbon, nitrogen, oxygen, fluorine, silicon, phosphorus, sulfur, and chlorine atomic centres in neutral molecules as well as anions H(−), OH(−), and F(−). The empty radial 2pr vacant orbital on the carbon centre in CB11H11, which corresponds to the LUMO, acts as a Lewis acid or electron attractor, as shown by the molecular electrostatic potential (MEP) and electron localization function (ELF). The thermochemistry and topological analysis of the complexes {CB11H11:LB} are comprehensively analysed and classified according to shared or closed-shell interactions. ELF analysis shows that the tetrel C⋯X bond ranges from very polarised bonds, as in H11B11C:F(-) to very weak interactions as in H11B11C⋯FH and H11B11C⋯O=C=O.

Tetrel Bonding in CB11H11 Carbonium Ylide

High-level quantum-chemical computations (G4MP2) are carried out in the study of complexes featuring tetrel bonding between the carbon atom in the carbenoid CB11H11 - obtained by hydride removal in the C-H bond of the known closo-monocarbadodecaborate anion CB11H12() and acting as Lewis acid (LA) - and Lewis bases (LB) of different type; the electron donor groups in the tetrel bond feature carbon, nitrogen, oxygen, fluorine, silicon, phosphorus, sulphur and chlorine atomic centers in neutral molecules as well as anions H(-), OH(-) and F(-). The empty radial 2pr vacant orbital on the carbon center in CB11H11 , which corresponds to the LUMO, acts as a Lewis acid or electron attractor, as shown by the molecular electrostatic potential (MEP) and electron localization funcion (ELF). The thermochemistry and topological analysis of the complexes {CB11H11:LB} are comprehensively analyzed, and classified according to sharing or closed-shell interactions. ELF analysis shows that the tetrel C···X bond ranges from very polarised bonds, as in H11B11C:F() to very weak interactions as in H11B11C···FH and H11B11C···O=C=O.

Torquoselectivity of the Ring-Opening Reaction of 3,3-Dihalosubstituted Cyclobutenes: Lone Pair Repulsion and Cyclic Orbital Interaction

<div><div>Three major factors determine torquoselectivity, which is the diastereoselectivity in electrocyclic ring-opening reactions to produce <i>E</i>/<i>Z</i>-double bond(s). One is the interaction between the decomposing s_CC bond and low-lying vacant orbital(s), such as a p*- or s*-orbital on the substituent, which promotes the reaction, resulting in inward rotation of the substituent. Second, for a substituent with a lone pair(s), repulsive interaction between the decomposing s-bond and the lone pair(s) hinders inward rotation, so that the products of outward rotation should be preferred. Finally, a more strongly donating s-electron-donating group (sEDG) rotates inwardly due to stabilization by phase-continuous cyclic orbital interaction. We compared the latter two interactions, repulsion between the lone pairs on the substituent and stabilization from phase-continuous cyclic orbital interaction, to determine which has a greater effect on the diastereoselectivity. We considered a series of model reactions with halogen substituents, and concluded that the diastereoselectivity is mainly controlled by cyclic orbital interaction.<br></div></div>

Torquoselectivity of the Ring-Opening Reaction of 3,3-Dihalosubstituted Cyclobutenes: Lone Pair Repulsion and Cyclic Orbital Interaction

<div><div>Three major factors determine torquoselectivity, which is the diastereoselectivity in electrocyclic ring-opening reactions to produce <i>E</i>/<i>Z</i>-double bond(s). One is the interaction between the decomposing s_CC bond and low-lying vacant orbital(s), such as a p*- or s*-orbital on the substituent, which promotes the reaction, resulting in inward rotation of the substituent. Second, for a substituent with a lone pair(s), repulsive interaction between the decomposing s-bond and the lone pair(s) hinders inward rotation, so that the products of outward rotation should be preferred. Finally, a more strongly donating s-electron-donating group (sEDG) rotates inwardly due to stabilization by phase-continuous cyclic orbital interaction. We compared the latter two interactions, repulsion between the lone pairs on the substituent and stabilization from phase-continuous cyclic orbital interaction, to determine which has a greater effect on the diastereoselectivity. We considered a series of model reactions with halogen substituents, and concluded that the diastereoselectivity is mainly controlled by cyclic orbital interaction.<br></div></div>

Torquoselectivity of the Ring-Opening Reaction of 3,3-Dihalosubstituted Cyclobutenes: Lone Pair Repulsion and Cyclic Orbital Interaction

<div><div>Three major factors determine torquoselectivity, which is the diastereoselectivity in electrocyclic ring-opening reactions to produce <i>E</i>/<i>Z</i>-double bond(s). One is the interaction between the decomposing s_CC bond and low-lying vacant orbital(s), such as a p*- or s*-orbital on the substituent, which promotes the reaction, resulting in inward rotation of the substituent. Second, for a substituent with a lone pair(s), repulsive interaction between the decomposing s-bond and the lone pair(s) hinders inward rotation, so that the products of outward rotation should be preferred. Finally, a more strongly donating s-electron-donating group (sEDG) rotates inwardly due to stabilization by phase-continuous cyclic orbital interaction. We compared the latter two interactions, repulsion between the lone pairs on the substituent and stabilization from phase-continuous cyclic orbital interaction, to determine which has a greater effect on the diastereoselectivity. We considered a series of model reactions with halogen substituents, and concluded that the diastereoselectivity is mainly controlled by cyclic orbital interaction.<br></div></div>

Structures, Energies, and Bonding Analysis of Monoaurated Complexes with N-Heterocyclic Carbene and Analogues

In this work, we computationally investigated from quantum chemical calculations (DFT) at the BP86 level with the various basis sets def2-SVP, def2-TZVPP, and TZ2P+, chemical bonding issues of the recently described carbene-analogues gold(I) complexes AuCl-NHEMe (Au1-NHE) with E = C – Pb. The optimized structures and the metal-ligand bond dissociation energy (BDE) were calculated, and the nature of the E→Au bond was studied with charge and energy decomposition methods. The equilibrium structures of the system showed that there were major differences in the bonded orientation from the ligands NHC-NHPb to gold(I) complex between the lighter and the heavier homologues. The BDEs results showed that the metal-carbene analogues bonds were very strong bonds and the strongest bond was calculated for Au1-NHC which had the bond strength De = 79.2 kcal/mol. Bonding analysis of Au1-NHE showed that NHE ligands exhibited donor-acceptor bonds with the σ lone pair electrons of NHE donated into the vacant orbital of the acceptor fragment (AuCl). The EDA-NOCV results indicated that the ligand NHE in Au1-NHE complexes were strong σ-donors and very weak π donor and the bond order in complexes was Au1-NHC > Au1-NHSi > Au1-NHGe > Au1-NHSn > Au1-NHPb. We also realised that the gold-ligand bond was characterized by a π back-donation component from the Au to the ligand. All investigated complexes in this study were suitable targets for synthesis and gave a challenge in designing Au nano-crystals of narrow size distribution from gold(I) complexes that carried versatile N-heterocyclic carbene-analogues NHE.

ESR Study of K-Mo2C for Increased Catalytic Properties

The presence of potassium in molybdenum carbide morphology has been reported to increase the selectivity and reactivity of its catalytic properties. Potassium with its tendency to donate electron will enhance the electron density at the surface of catalyst by donating its electron at the vacant orbital framework either to carbon or metal moiety. This phenomenon will cause temporary paramagnetic properties of the catalyst and can be easily detected using an ESR spectrometer. In this paper, an ESR-based study to identify and prove that donating electron does take place at Mo2C after being promoted with potassium was conducted. Introduction of H2and UV radiation were also carried out for comparison.The result from ESR spectra showed that in the absence of potassium in the Mo2C, no ESR signal was observed. However, in the presence of potassium, a singlet peak with g value ca. 1.9723 was found. The presence of a single peak indicated that the donated electron did not interact with any nearby nucleus in the surroundings. Deviation value of 2.0023 for free electron, indicates that this donated an electron probably interacted with an empty 4d orbital from molybdenum or 2p orbital from carbon.In the introduction of H2gas and UV radiation, the finding showed that an increasing trend of singlet peak in the ESR spectrum earlier was observed. The trend indicated that the splitting of H2by UV radiation generated new electron and joined the donated electron from K circulating at the surface of K-Mo2C morphology without interacting with another nucleus.