Strong Bases Design: Key Techniques and Stability Issues

Theoretical design of molecular superbases has been attracting researchers for more than twenty years. General approaches were developed to make the bases potentially stronger, but less attention was paid to the stability of the predicted structures. Hence, only a small fraction of the theoretical research has led to positive experimental results. Possible stability issues of extremely strong bases are extensively studied in this work using quantum chemical calculations on a high level of theory. Several step-by-step design examples are discussed in detail, and general recommendations are given to avoid the most common stability problems. New potentially stable structures are theoretically studied to demonstrate the future prospects of molecular superbases design.

Exploiting the (-C-H···C-) Interaction to Design Cage-Functionalized Organic Superbases and Hyperbases: A Computational Study

A set of carbon center-based P-ylidesubstituting bases have been exploited computationally with pentacyclo[5.4.0.02,6.03,10.05.9]undecane (PCU) and pentacyclo [6.4.0.02,7.03,11.06,10] dodecane (PCD) scaffolds using the B3LYP-D3/6-311+G(d,p) level of theory. The proton affinities calculated in the gas phase are in the range of superbases and hyperbases. The Atomsin-Molecules and Natural Bond Orbital calculations reveal that the -C-H···C- interaction plays a substantial role in improving the basicity, and tuning the -C-H···C- interaction can enhance the basicity of such systems. The free activation energy for proton exchange for PCD and PCU scaffolds substituted with P-ylide is substantially low. The computed results reveal the strength and nature of such - C-H···C- interactions compared to the -N-H···N- hydrogen bonds. The isodesmic reactions suggest that the superbasicity achieved using these frameworks arises from a combination of several factors, such as the ring strain of the bases in their unprotonated form, steric repulsion, and the intramolecular -C-H···C- interaction.

The design of C2-chiral bases with dual basic sites predicted to exceed the range of superbasicity: a computational study

A set of C2-chiral bases with bis-protonation sites (1–9) on dimethyl-binaphthalene derivatives have been explored using the B3LYP/6-311+G(d,p) level and the proton affinities calculated are in the range of superbases for both the sites.

Gas-phase basicity and proton affinity measurements of Alzheimer's disease drugs by the extended kinetic method and a theoretical investigation

This study has been carried out to obtain the thermochemical parameters of drugs used for Alzheimer's disease. The measurement of gas-phase basicity (GB) and proton affinity (PA) values of four important and commercially available drugs for Alzheimer's disease namely, rivastigmine, galantamine, memantine, and tacrine, is attempted for the first time. This study also includes the measurement of GB and PA values for the proposed drug curcumin, a natural product. We calculated the GB and PA values for all these drugs by applying electrospray ionization tandem mass spectrometry (ESI-MS/MS) with the extended kinetic method. Since, all these drugs possessing amino groups (basic nature), the PA values for all these drugs are high i.e., the PA values range from 923.6 to 979.7 kJ/mol and the GB values range from 886.2 to 943.3 kJ/mol. The GB and PA values obtained from the mass spectrometric experiments are well supported with the theoretical calculations. A high-level theoretical B3LYP/6-311 + G(d,p) method is used for the PA and GB calculation and the deviations are in the acceptable range.

The effect of σ/π, σ and π donors on the basicity of silylene superbases: a density functional theory study

In this study, we examined computationally that the combination of π-and σ-donor substituents results in higher basicity of silylene compounds compared to the usage of π-donor substituents alone.

Facile one-pot synthesis of a 3-azabicyclo[3.3.1]nonane scaffold by a tandem Mannich reaction

Various 3-azabicyclo[3.3.1]nonane derivatives are readily synthesized directly from aromatic ketones, paraformaldehyde and dimethylamine via a novel one-pot tandem Mannich annulation.

Water-Lean Solvents for Post-Combustion CO2 Capture: Fundamentals, Uncertainties, Opportunities, and Outlook

This review is designed to foster the discussion regarding the viability of postcombustion CO₂ capture by water-lean solvents, by separating fact from fiction for both skeptics and advocates. We highlight the unique physical and thermodynamic properties of notable water-lean solvents, with a discussion of how such properties could translate to efficiency gains compared to aqueous amines. The scope of this review ranges from the purely fundamental molecular-level processes that govern solvent behavior to bench-scale testing, through process engineering and projections of process performance and cost. Key discussions of higher than expected CO₂ mass transfer, water tolerance, and compatibility with current infrastructure are presented along with current limitations and suggested areas where further solvent development is needed. We conclude with an outlook of the status of the field and assess the viability of water-lean solvents for postcombustion CO₂ capture.

The role of non-covalent interaction for the adsorption of CO2 and hydrocarbons with per-hydroxylated pillar[6]arene: a computational study

A systematic study has been performed with DFT calculations for the physisorption of CO₂, CH₄, and n-butane gases by pillar[6]arene (PA[6]) in gas phase.

In silico design of adamantane derived organic superbases with an extended hydrogen bond network and their use as molecular containers for the storage of H2 and CO2

DFT calculations predicted that amine substituted adamantane derivatives can function as organic superbases and can be used for gas storage.

Reaction of benzopinacol with non-ionic bases: reversing the pinacol coupling

The reaction of benzopinacol with the non-ionic bases butyllithium and phosphazene P4 leads to the formation of the corresponding ketyl radical anions, which have been characterized by EPR/ENDOR spectroscopy. This conversion has a high efficiency. Such a reversed pinacol reaction can be used for a controlled release of ketyl radicals. Moreover, the nature of the base has a marked effect on the association of the ketyl radical anion and the counterions. This illustrates the importance of ion pairing for reductive coupling.

Enhancing and modulating the intrinsic acidity of imidazole and pyrazole through beryllium bonds

The structure and electronic properties of the complexes formed by the interaction of imidazole and pyrazole with different BeXH(BeX2) (X = H, Me, F, Cl) derivatives have been investigated via B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d,p) calculations. The formation of these azole:BeXH(BeX2) complexes is accompanied by a dramatic enhancement of the intrinsic acidity of the azole, as the deprotonated azole is much more stable after the aforementioned interaction. Most importantly, the increase in acidity is so large that the azole:BeXH or azole:BeX2 complexes behave as NH acids, which are stronger than typical oxyacids such as phosphoric acid and oxalic acid. Interestingly, the increase in acidity can be tuned through appropriate selection of the substituents attached to the Be atom, permitting us to modulate the electron-accepting ability of the BeXH or BeX2 molecule.