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The cycloaddition of ethylene, cyanoethylene, and propylene to a five-membered P/B frustrated Lewis pair (FLP) is shown to be highly favorable under normal conditions, as confirmed by the computed thermodynamic and kinetic data. All of these cycloaddition reactions are concerted as highlighted by the intrinsic reaction coordinate (IRC) and Wiberg bond index calculations. Almost 70% of the reaction force is required for structural orientation to initiate electronic activity. The reactions are interpreted by the frontier molecular orbital (FMO) analysis and conceptual density functional theory (DFT)-based reactivity descriptors. It appears that ethylene and propylene will act as nucleophiles, while the FLP will act as an electrophile throughout the cycloaddition reaction, however, cyanoethylene will act as an electrophile and the FLP as a nucleophile. Regioselectivities of the cycloadditon of cyanoethylene and propylene to the FLP are further verified through philicity and dual descriptors. It is demonstrated that an FLP can be forced to act as an electrophile or a nucleophile by intelligently selecting its partner in a cycloaddition reaction. Even the P and B centers would behave differently within the same FLP. This strategy may be properly exploited by the experimentalists in designing a suitable reaction for the synthesis of any useful molecule possessing the desired property.

A DFT-based computational study has been performed on the hydrogenation of CO2, catalyzed by a bridged FLP. Formic acid might be formed in two possible pathways as revealed by this study. In one way, the Lewis basic center of the FLP activates H2, and the Lewis acidic center activates CO2 simultaneously in the first step of the reaction. Alternatively, the Lewis basic center of the FLP activates CO2, and the Lewis acidic center activates H2. The simultaneous activation of CO2 and H2 through single TS is confirmed by NBO analysis. Free energy profiles are also generated for both the possible pathways in solvent phase. It appears from these profiles that the first step, i.e., simultaneous activation of CO2 and H2, is the rate determining for both the reaction pathways. A significant amount of barrier height is reduced in comparison to that in the corresponding uncatalyzed reaction as observed in these profiles. The nature of donor-acceptor interactions present in the transition state geometries is further analyzed by energy decomposition analysis (EDA) methods. The EDA analysis shows that the HOMO of the FLP donates electron density to the LUMO of H2, the HOMO of H2 donates electron density to the LUMO of CO2, and several occupied MOs of CO2 donate electron density to the LUMO of FLP at the TS geometry.

The role of boron–ligand cooperation in activating molecular hydrogen by a set of six frustrated Lewis pair (FLP) systems is explored using density functional theory. The results obtained from thermochemical calculations show that all the studied FLP systems are capable of activating molecular hydrogen as the activation free energies are not too high (17.6–25.6 kcal mol−1). Sulphur based FLP 6 is the most promising one as it results in the smallest activation barrier among the studied sets. For a given FLP, the introduction of an electron donating –NMe2 group at the para position of the pyridine ring somewhat lowers the barrier and enhances the B–X (X = O, N, S) interaction. The B–X bond present within the FLPs plays a crucial role in facilitating the H2 activation process where it gets changed from the B+–X− type of interaction in the FLP to the B ← X dative bond upon H2 activation as understood from the energy decomposition analysis in combination with the natural orbital for chemical valence theory (EDA-NOCV). This mode of operation is termed as boron–ligand cooperation in analogy with the metal–ligand cooperation in transition metal complexes. The EDA-NOCV results obtained at the TS also support an electron transfer model where simultaneous electron transfer takes place from the Lewis basic center (N) of the FLP to σ*(H2) and from σ(H2) to the Lewis acidic center (B) of the FLP, resulting in a weakened H–H bond. The change in the aromaticity of the pyridine rings during the course of H2 activation is also monitored by nucleus independent chemical shift calculations. Finally, the ability of the studied FLP systems to act as hydrogenation catalysts is elucidated by studying the hydrogenation of CO2 to yield formic acid.

The mechanism of dihydrogen activation has been theoretically investigated by means of DFT calculation. An experimentally synthesized bridged P/B frustrated Lewis pair (FLP) and two designed FLPs are used for this purpose. The model FLPs 2 and 3 are more efficient than FLP 1 for H2 activation as revealed by the thermochemical and kinetic data. A significant amount of electron density is transferred from H2 molecule to the FLPs at the transition states (TSs) during the process of H2 activation, and this is greater at the corresponding TSs of FLPs 2 and 3 than that of FLP 1. The NICS(0) and NICS(1zz) of the boron heterocycle at the FLPs 2 and 3, and at the corresponding TSs and the product geometries of H2 activation demonstrate that the anti-aromatic character of the rings in the FLPs is remarkably reduced at the TSs and finally at the products and that is most likely responsible for enhanced activity of FLPs 2 and 3 by decreasing the activation barrier.

The noble gas (Ng) binding ability of a monocationic [(FLP)Au]+ species has been investigated by a computational study. Here, the monocationic [(FLP)Au]+ species is formed by coordination of Au(I) cation with the phosphorous (Lewis base) and the boron (Lewis acid) centers of a frustrated Lewis pair (FLP). The bonds involving Au and P, and Au and B atoms in [(FLP)Au]+ are partially covalent in nature as revealed by Wiberg bond index (WBI) values, electron density analysis and energy decomposition analysis (EDA). The zero point energy corrected bond dissociation energy (D0), enthalpy and free energy changes are computed for the dissociation of Au-Ng bonds to assess the Ng binding ability of [(FLP)Au]+ species. The D0 ranges from 6.0 to 13.3 kcal/mol, which increases from Ar to Rn. Moreover, the dissociation of Au-Ng bonds is endothermic as well as endergonic for Ng = Kr-Rn, whereas the same for Ng = Ar is endothermic but exergonic at room temperature. The partial covalent character of the bonds between Au and Ng atoms is demonstrated by their WBI values and electron density analysis. The Ng atoms get slight positive charges of 0.11–0.23 |e|, which indicates some amount of charge transfer takes place from it. EDA demonstrates that electrostatic and orbital interactions have equal contributions to stabilize the Ng-Au bonds in the [(FLP)AuNg]+ complex.

The hexagonal and heptagonal holes of B 39 - allow its complexation with a half sandwich complex ECp∗+ (E Si, Ge, Sn, Pb). Structure and the nature of bonding of (η6/7-B39)E(η5-Cp∗) are explored through the density functional theory based computation. (η6-B39)E(η5-Cp∗) isomers are more stable than (η7-B39)E(η5-Cp∗) and the energy difference between these two isomers decreases down the group from Si to Pb. The dissociation path, (η6/7-B39)E(η5-Cp∗) → B 39 - + ECp∗+ is studied. For all E, (η6/7-B39)E(η5-Cp∗) is formed exergonically at 298 K temperature as given by the ΔG values of dissociation path [60.1(Si) to 68.3(Pb) kcal/mol for (η6-B39)E(η5-Cp∗) and 58.3(Si) to 67.8(Pb) kcal/mol for (η7-B39)E(η5-Cp∗)]. The adduct becomes bent around the central E atom when B 39 - gets attached to ECp∗+ and the amount of bending increases gradually down the group from Si to Pb. Bonding analysis of the stable isomer, (η6-B39)E(η5-Cp∗) has been done by natural bonding orbital (NBO) and energy decomposition analyses (EDA). The electron density from B 39 - is transferred to the ECp∗+ moiety as revealed by the NBO analysis. All the complexes are mainly stabilized by the electrostatic and orbital interactions between B 39 - and ECp∗+ fragments as highlighted by the EDA results.

The efficacy of B40 borospherene to act as a host for noble gas atoms is explored via density functional theory based computations. Although the Ng@B40 complexes are thermochemically unstable with respect to dissociation into free Ng and B40, it does not rule out their viability as all the systems possess a high activation free energy barrier (84.7-206.3 kcal mol-1). Therefore, once they are formed, it is hard to take out the Ng atom. Two Ng atoms can also be incorporated within B40 for the lighter Ng atoms (He and Ne). In fact, the destabilization offered by the encapsulation of one and two He atoms and one Ne atom inside B40 is significantly less than that in experimentally synthesized He@C20H20, highlighting their greater possibility for synthesis. Although Ar2 and Kr2 encapsulated B40 systems are very much destabilized by the repulsive interaction between Ng2 and B40, an inspection of the bonding situation reveals that the confinement can even induce some degree of covalent interaction between two otherwise non-bonded Ng atoms. Ng atoms transfer electrons towards B40 which is smaller for lighter Ng atoms and gradually increases along He to Rn. Even if the electrostatic interaction between Ng and B40 is the most predominant term in these systems, the extent of the orbital interaction is also considerable. However, the very large Pauli repulsion counterbalances the attractive interaction, eventually turning the interaction repulsive in nature. Ng@B40 also shows dynamical behaviour involving continuous exchange between hexagonal and heptagonal holes, similar to the host cage, as understood from the very little variation in the activation barrier because of the Ng encapsulation. Furthermore, sandwich complexes like [(η5-C5Me5)Fe(η6-B40)]+ and [(η5-C5Me5)Fe(η7-B40)]+ are noted to be viable with the latter being slightly more stable than the former. The encapsulation of Xe slightly improves the dissociation energy associated with the decomposition into Xe@B40 and [Fe(η5-C5Me5)]+ compared to that in the bare one.

The activation of allene by a five-membered P/B frustrated Lewis pair (FLP) has been explored by DFT based computational study. It reveals the addition of allene to the FLP takes place via two thermodynamically favorable path. But, the attack of the P center of the FLP to the middle carbon of allene is kinetically more preferable. The reaction is further analysed by taking methyl-allene and cyano-allene and which produce four thermodynamically favorable regioisomers. However the attack of the P center of the FLP to the middle carbon is kinetically more preferable. The mechanism of the reactions are carefully analysed.

A density functional theory based study is performed to investigate the noble gas (Ng = Ar-Rn) binding ability of nitrates, sulfates and carbonates of noble metal (M). Their ability to bind Ng atoms is assessed through bond dissociation energy and thermochemical parameters like dissociation enthalpy and dissociation free energy change corresponding to the dissociation of Ng bound compound producing Ng and the respective salt. The zero-point energy corrected dissociation energy values per Ng atom for the dissociation process producing Ng atom(s) and the corresponding salts range within 6.0–13.1 kcal/mol in NgCuNO3, 3.1–9.8 kcal/mol in NgAgNO3, 6.0–13.2 kcal/mol in NgCuSO4, 3.2–10.1 kcal/mol in NgAgSO4, 5.1–11.7 kcal/mol in Ng2Cu2SO4, 2.5–8.6 kcal/mol in Ng2Ag2SO4, 8.1–19.9 kcal/mol in Ng2Au2SO4, 5.7–12.4 kcal/mol in NgCuCO3, 2.3–8.0 kcal/mol in Ng2Ag2CO3 and 7.3–18.2 kcal/mol in Ng2Au2CO3, with a gradual increase in moving from Ar to Rn. For a given type of system, the stability of Ng bound analogues follows the order as Au > Cu > Ag. All dissociation processes are endothermic in nature whereas they become endergonic as well in most of the cases of Kr-Rn bound analogues at 298 K. Natural population analysis along with the computation of Wiberg bond indices, and electron density analyses provide insights into the nature of the Ng-M bonds. The Ng-M bonds can be represented as partial covalent bonds as supported by the different electron density descriptors.

A density functional theory study is performed to predict the structures and stability of carbon monoxide (CO) bound EX3+ (E = C, Si, Ge, Sn, Pb; X = H, F, Cl, Br, I) complexes. The possibility of bonding through both C- and O-sides of CO is considered. Thermochemical analysis reveals that all the dissociation processes producing CO and EX3+ are endothermic in nature whereas most of the dissociation reactions are endergonic in nature at room temperature. The nature of bonding in EC/O bonds is analyzed via Wiberg bond index, natural population analysis, electron density, and energy decomposition analyses in conjunction with natural orbitals for chemical valence scheme. In comparison to CO stretching frequency ( ν∼CO) in free CO, while a red shift is noted in O-side binding, the C-side binding results in a blue shift in ν∼CO. The relative change in ν∼CO values in CO bound EX3+ complexes on changing either E or X is scrutinized and possible explanation is provided in terms of polarization in the σ- and π-orbitals and the relative strength of C→E or O→E σ-donation and E→C or E→O π-back-donation. © 2016 Wiley Periodicals, Inc.

The impact of the size of the confining regime on the thermodynamic and kinetic outcome of a representative Diels-Alder reaction between ethylene and 1,3 butadiene has been investigated in silico. To this end, two organic hosts namely cucurbit[6]uril (CB[6]) and cucurbit[8]uril (CB[8]) have been considered in order to impose confinement on the reactants/transition state/product of the concerned reaction. The obtained results have been compared with the recently reported (Chakraborty et al. ChemPhysChem 18:2162-2170, 2017) corresponding case of the same reaction happening inside cucurbit[7]uril (CB[7]). Results indicate that as compared to the reaction of ethylene and 1,3 butadiene inside CB[7], both CB[6] and CB[8] cavitands slow down the same reaction at 298.15 K and 1 atm. It appears that the size of the cavitand plays a crucial role in affecting the kinetic outcome of the considered reaction. While CB[7] can enforce productive alignment of the reactants inside its cavity thereby facilitating the reaction, neither CB[6] nor CB[8] can perform the same task as effectively. This situation bears qualitative resemblance with the cases of enzyme catalyzed reactions.