Unveiling the Obscure Potential of o-carborane Based IFLPs for CO2 Sequestration.

Sequestering carbon dioxide (CO2) from the atmosphere is necessary to achieve a sustainable environment. The emergence of frustrated Lewis pairs (FLPs) has opened a new dimension in the development of organocatalysts for CO2 sequestration. To date, various FLPs have been developed for CO2 sequestration, yet the quest for robust FLPs continues. Based on the intriguing electronic effects of the carborane polyhedral, o-carboranes can be projected as a versatile bridging unit for intramolecular FLPs (IFLPs). In the present work, o-carborane based IFLPs AlP, BP, AlN and BN have been proposed for the activation of CO2 molecule. The density functional theory (DFT) based calculations and thorough orbital analysis have been carried out to extensively study the electronic structure of the o-carborane unit. The proposed IFLPs were systematically compared with their corresponding phenyl bridged analogues to assess the effect of o-carborane bridging unit on the reactivity of the acidic and basic sites. The results show that the o-carborane supported IFLPs are more reactive towards CO2 than the phenyl bridged IFLPs. Also, placing the basic site on the B atom at the 4th position of the o-carborane bridge rather than the C atom at the 2nd position results in more reactive IFLPs.

Orbital and free energy landscape expedition towards the unexplored catalytic realm of aromatically modified FLPs for CO2 sequestration.

The emergence of frustrated Lewis pairs (FLPs) has created a whole new dimension in the development of metal free catalysts for CO2 sequestration. Efforts have been made to enhance the catalytic activity of the FLPs. The aromatic modulation of the catalytic sites has been successfully demonstrated to enhance the activity towards CO2. Although various aromatically modified geminal FLPs have been investigated for CO2 capture, the catalytic space of these FLPs has not been fully resolved yet. Thus, to fulfil the knowledge gap in the understanding of the catalytic behaviour and to extend the concept of aromatically enhanced FLPs, in the present study all the possible combinations of aromatic and antiaromatic modulations of the acidic and basic sites have been proposed and examined using density functional theory based orbital analysis. Further to verify the results obtained from the orbital analysis and to fully explore the catalytic space of the proposed systems, free energy landscapes have been examined using metadynamics simulations. The detailed intrinsic bond orbital (IBO) and principal interacting orbital (PIO) analyses capture crucial details of the reactions. Furthermore, evolution of anisotropy of induced current density (AICD) along the reaction justifies the effect of aromatic/antiaromatic modulation on the catalytic sites. The results show that highly asynchronous mechanisms have been found due to the aromatic/antiaromatic modulations. The simultaneous favourable aromatic/antiaromatic modification on the acidic and basic sites may greatly reduce the CO2 activation barrier. The enhancement of the acidic character of the B atom in the intramolecular FLPs (IFLPs) leads to a thermodynamically more feasible reaction with stable CO2 adducts. The acidic site has been found to play a major role in controlling the kinetics and thermodynamics of the reaction. This study provides valuable insights into the catalytic realm of the aromatically modified FLPs, which can be utilized to design more efficient and specific next-generation FLPs.

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.

PIO and IBO analysis to unravel the hidden details of the CO2 sequestration mechanism of aromatically tempered N/B-based IFLPs.

Enhancing the catalytic reactivity of Frustrated Lewis Pairs (FLPs) in various activities such as CO2 activation and sequestration has recently gained interest among researchers around the globe. A recent investigation showed the use of aromaticity as a tool to modulate the catalytic behaviour of FLPs, establishing a whole new dimension in this area. In this work, aromatically tempered N/B-based intramolecular frustrated Lewis Pairs (IFLPs) are proposed for CO2 sequestration. Density functional theory (DFT)-based calculations were carried out to probe the reaction mechanism. The detailed mechanistic investigation was carried out using intrinsic reaction coordinate (IRC), principal interacting orbital (PIO), intrinsic bond orbital (IBO) and natural bonding orbital (NBO) analyses. The results show that aromatic gain in the system at the basic sites lowers the activation barrier, whereas the antiaromatic gain results in increased activation energy. The sequestration mechanism was found to be an asynchronous concerted mechanism, and polar solvents result in higher asynchronicity. This work, for the first time, reports asynchronicity in the catalytic behavior of aromatically tempered IFLPs, which can be crucial to designing better IFLPs for CO2 sequestration.

Unprecedented Activation of CO2 by α-Amino Boronic Acids.

Efficient and environmentally benign transformation of carbon dioxide (CO2) into valuable chemicals is mainly obstructed by the lack of suitable catalysts. To date, various catalysts have already been investigated for the conversion of CO2 molecules, but still finding metal-free, simple, and environment-friendly catalysts is a topic of utmost interest among researchers. Thus, in this regard, the present work projects α-amino boronic acids (AABs) as a metal-free and simple catalyst for CO2 activation. The density functional theory (DFT)-based calculations have been carried out to explore the catalytic potential of AABs. The detailed electronic structure analysis of the considered AABs unveils the catalytic similarities with frustrated Lewis pairs (FLPs) in a gas phase. Interestingly, a peculiar catalytic action of AABs has been observed in the presence of solvents. The contrasting catalytic behavior of AABs in solvents has been extensively investigated by employing principal interacting orbital (PIO), intrinsic bond orbital (IBO), and natural bond orbital (NBO) analyses along the reaction paths. The results of the orbital studies provide concrete ground for the observed reaction mechanism. Further, the energetic analysis of the reaction of CO2 with AABs reveals that <5 kcal/mol energy is required for activation in a solvent phase, and the formed adducts are readily active. These observations show that AABs can be considered as an efficient catalyst for CO2 activation.

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.

Alanine boronic acid functionalized UiO-66 MOF as a nanoreactor for the conversion of CO2 into formic acid.

The alarming increase in the atmospheric CO2 concertation is a global concern today. Thus, the researchers around the globe are finding ways to decrease the amount of CO2 in the atmosphere. Converting CO2 into valuable chemicals like formic acid is one of the best ways to address this issue, but the stability of the CO2 molecule poses a great challenge in its conversion. To date various metal-based and organic catalysts are available for the reduction of CO2 . Still there is a great need for better, robust and economic catalytic systems and the advent of functionalized nanoreactors based on metal organic frame works (MOF) have opened a new dimension in this field. Thus, in the present work UiO-66 MOF functionalized with alanine boronic acid (AB) have been theoretically investigated for the reaction of CO2 with H2 . The density functional theory (DFT) based calculations were carried out to probe the reaction pathway. The result shows that the proposed nanoreactors can efficiently catalyze the CO2 hydrogenation. Further, the periodic energy decomposition analysis (pEDA) unveils important insights about the catalytic action of the nanoreactor.

Novel Insight into the Molecular Frustration of IFLPs Based on Boron-Functionalized Pyrimidines for CO2 Sequestration.

The emergence of frustrated Lewis pairs (FLPs) as organocatalysts for CO2 sequestration has opened a new dimension in this area. To date, various inter- and intramolecular frustrated Lewis pairs have been experimentally and theoretically explored for CO2 activation, still there is plenty of room for new insights into FLPs. Thus, in the present study intramolecular frustrated Lewis pairs (IFLPs) based on boron-functionalized pyrimidines have been proposed for CO2 activation and computationally investigated to gain new insights into the molecular frustration. The extensive natural bond orbital (NBO) analysis unveils an interesting relationship between the orbital charge transfer and the activity. The result shows that the greater the charge transfer between the acidic and basic sites, the higher will be the frustration in the molecule. Also, the presence of atoms bearing a lone pair attached to the acidic site relieves the frustration by charge transfer. Based on the orbital charge transfer, the predicted activity order for the proposed IFLPs is supported by the energetics for the reaction of CO2 with the IFLPs. Further, the activation strain analysis (ASA) provides a different viewpoint about the reactivities of the IFLPs and highlights the importance of the geometrical structure of the catalyst. Furthermore, the ab initio molecular dynamics (AIMD) uplights the reversibility of the formed products.

Boron based intramolecular heterocyclic frustrated Lewis pairs as organocatalysts for CO2 adsorption and activation.

The massive increase in the amount of carbon dioxide (CO2 ) in the atmosphere has led to serious environmental problems. One of the best ways to tackle this problem is the CO2 capture and its utilization as a C1 carbon source for the production of industrially valuable chemicals. But the thermodynamic stability of the CO2 molecule poses a great challenge in its transformation. Since the last two decades, various metal-based and organic catalysts have been developed for the adsorption and activation of CO2 . Among all the catalysts the Frustrated Lewis pairs (FLPs) have been shown great potential in CO2 capture and conversion. Thus, in the present work, Intramolecular Frustrated Lewis pairs (IFLP) based on N-Heterocycles with boron group functionalization at the α-position to N has been theoretically investigated for CO2 activation. Thorough orbital analysis has been carried out to investigate the reactivity of the proposed catalytic systems. The result shows that the considered IFLPs are capable of activating CO2 with minimum energy requirements. The CO2 activation energy range between 8 and 14 kcal/mol. The non-polar solvent was found to be the suitable medium for the reaction. Also, the reversibility of the adducts formed with the IFLPs can be controlled by appropriate substitution at B atom in the IFLPs.