Dissociative Adsorption of H2 S on Li(110) Surface Using Density Functional Theory Calculations and Car-Parrinello Molecular Dynamics Simulations

Bispericyclic Ambimodal Dimerization of Pentafulvene: The Origin of Asynchronicity and Kinetic Selectivity of the Endo Transition State

The propensity of fulvenes to undergo dimerization has long been known, although the in-depth mechanism and electronic behavior during dimerization are still elusive. Herein, we made an attempt to gain insights into the reactivity of pentafulvene for Diels-Alder (DA) and [6 + 4]-cycloadditions via conventional and ambimodal routes. The result emphasizes that pentafulvene dimerization preferentially proceeds through a unique bifurcation mechanism where two DA pathways merge together to produce two degenerate [4 + 2]-cycloadducts from a single TS. Despite the [6 + 4]-cycloadduct being thermodynamically preferred, [4 + 2]-cycloaddition reactions are kinetically driven. Singlet biradicaloid is involved in through-space 6e- delocalization as a secondary orbital interaction that originates asynchronicity and stabilizes the bispericyclic transition state (TS). The transformation of various actively participating intrinsic bonding orbitals (IBOs) unambiguously forecasts the formation of multiple products from a single TS and rationalizes the mechanism of ambimodal reactions that are rather difficult to probe with other analyses. The changes in active IBOs clearly distinguish the conventional reactions from bifurcation reactions and can be employed to characterize and confirm the ambimodal mechanism. This report gains a crucial theoretical insight into the mechanism of bifurcation, the origin of asynchronicity, and electronic behavior in ambimodal TS, which will certainly be of enormous value for future studies.

Electronic and photophysical properties of an atomically thin bowl-shaped beryllene encapsulated inside the cavity of [6]cycloparaphenylene (Ben@[6]CPP)

Exotic metallic nanostructures are being intensely pursued for a myriad of applications, with ultrathin membranes currently at the heart of several investigations. The objective of the present study was to systematically assess the atom-by-atom encapsulation of Be in the molecular nanoring of [6]cycloparaphenylene ([6]CPP). Further, the study aimed to scrutinize the structure, stability, and properties of the encapsulated Ben@[6]CPP systems. The outcomes clearly revealed that [6]CPP enabled the cooperative confinement of atomically thin bowl-shaped beryllene inside its circular cavity. The confinement of Be in [6]CPP generated topologically anisotropic surfaces with distinct interior and exterior charge distributions. The Ben@[6]CPP complexes could render a cationic or anionic nature to Be depending on its neighbouring environment. Thus, the systems may offer a promising opportunity for the synergistic co-adsorption of multiple reactants that are involved in multicomponent reactions. Energy decomposition analysis (EDA) elucidated that the bonding between Be and [6]CPP was partially ionic and covalent in character. The progressive encapsulation of Be atoms inside the cavity of [6]CPP led to a red-shift of the excitation wavelength to the visible region. The calculated optical absorption coefficient was higher than 104 L mol-1 cm-1, which shows promise for diverse optoelectronic applications.

Enhanced Selectivity of the Propylene Epoxidation Reaction on a Cu Monolayer Surface via Eley-Rideal Mechanism

The aerobic oxidation of propylene to selectively achieve propylene oxide (PO) is a challenging reaction in catalysis. Therefore, an active catalyst which shows enhanced PO selectivity is extremely desired. In the present investigation, an attempt has been made to explore the catalytic activity of a mono-atomically thin two-dimensional (2D) hexagonal (HX) Cu layer for selective propylene epoxidation using molecular O₂ with the aid of density functional theory calculations. The results reveal that the conversion of propylene to PO via Eley-Rideal mechanism is an exoergic and barrierless reaction on the O₂ pre-adsorbed Cu monolayer. The Pauli energy component plays a decisive role for barrierless reaction whereas the electrostatic and orbital contribution governs the energetic stability of PO. Car-Parrinello molecular dynamics (CPMD) simulation reinforces the outcomes of climbing image nudged elastic band (CI-NEB) calculation. Further, the formation of oxametallacycle OMC-2 (0.47 eV) is kinetically favourable over OMC-1 (0.87 eV) and AHS (0.50 eV) on O pre-adsorbed 2D HX Cu. Interestingly, the energy barrier for the conversion of OMC-2 to PO (0.70 eV) is considerably low in comparison with the acetone formation (0.90 eV). Therefore, it is worth to mention that the 2D HX Cu surface provides a promising platform for selective propylene epoxidation.