Phosphinoborenium cations stabilized by N-heterocyclic carbenes: synthesis, structure, and reactivity.

Phosphinoborenium cations stabilized by N-heterocyclic carbenes (NHCs) were synthesized via the reaction of bromo(phosphino)boranes with NHCs. Their structures were investigated by heteronuclear magnetic resonance spectroscopy, X-ray diffraction, and density functional theory calculations. They possess a planar trigonal boron center directly bonded with the pyramidal phosphanyl group (PR2) and can be treated as cationic phosphinoboranes. The reactivity of the selected NHC-phosphinoborenium cation was tested toward AuCl·SMe2 and Ph2PCl. In both reactions, the titled compound acted as a phosphido group donor under heterolytic cleavage of the P-B bond. Control experiments with parent phosphinoborane emphasized differences between the reactivity of low-coordinate neutral and cationic species with P-B functionality.

Degradation of selected perfluoroalkyl substances (PFASs) using AlF3 in water.

The conversion of representative perfluorinated carboxylic acids and perfluorinated sulfonic acids in aqueous solutions into the corresponding perfluoroalkenes is investigated by using electronic structure methods. It is demonstrated that the use of aluminum trifluoride enables such conversions even at room temperature (with the reaction completion time not exceeding 1 minute). The mechanism of the reactions studied involves the withdrawal of F- from either the carboxylic or the sulfonic anion by AlF3 which leads to the formation of a stable AlF4- anion and a perfluoroalkene compound (which can be further decomposed to a series of nonfluorinated products) accompanied by CO2 or SO3 loss.

Application of nonmetallic frustrated cations in the activation of small molecules.

The concept of nonmetallic frustrated cations has been used in small molecule activation. The in situ generated ambiphilic phosphinoborinium cation activated phenyl isocyanate, diisopropylcarbodiimide, and acetonitrile under very mild conditions without any catalyst, yielding single-, double-, or mixed-activation products. Furthermore, the mechanisms of the reactions of the phosphinoborinium cation with small molecules were elucidated using density functional theory calculations.

An Excess Electron Bound to Magnesium Halides and Basic Grignard Compounds (RMgX and RMgR, R = Me, Et, Ph; X = F, Cl, Br).

Grignard reagents are commonly used in organic synthesis, yet their ability to form stable anionic states has not been recognized thus far. In this work, representative examples of RMgF, RMgCl, and RMgBr molecules involving methyl, ethyl, and phenyl functional groups serving as R substituents are investigated regarding their equilibrium structures, adiabatic electron affinities, and vertical electron detachment energies of their daughter anions. The electronic stabilities determined for the negatively charged Grignard compounds are then compared to those predicted for their corresponding magnesium halides. The anions formed by RMgX (R = Me, Et, Ph; X = F, Cl, Br) molecules are found to be adiabatically electronically stable valence-bound systems characterized by relatively large vertical electron detachment energies spanning the 0.79-1.62 eV range. In addition, significant structural relaxation upon attachment of an excess electron is predicted for all Grignard compounds considered. Furthermore, the re-examination of the anions formed by magnesium halides resulted in recognizing them as valence-bound rather than dipole-bound anions, in contrast to the earlier interpretations.

Icosahedral Carborane Superacids and their Conjugate Bases Comprising H, F, Cl, and CN Substituents: A Theoretical Investigation of Monomeric and Dimeric Cages.

Theoretical investigation of the H(CHB11 X11 ) (X=H, F, Cl, CN), H(CHB11 Xn Y11-n ) (X,Y=F, Cl; n=1,5), and dimeric (H(CHB11 X11 ))2 (X=F, Cl) carborane superacids performed at the B3LYP/6-311++G(d,p) theory level revealed the similarity of their equilibrium structures and the possibility of nearly barrierless hydrogen atom migration among the substituents attached to one side of the icosahedral CB11 cage. The vertical electron detachment energies predicted at the OVGF/6-311++G(3df,2pd) theory level for the conjugate bases (CHB11 X11 )- were found to span the 5.82-9.00 ev range. The acid strengths (manifested by the Gibbs free deprotonation energies spanning the 213-266 kcal/mol range) predicted for the icosahedral H(CHB11 X11 ) carborane systems confirm their superacidic properties which might be increased even further by the attachment of the second carborane H(CHB11 X11 ) unit that leads to a dimeric structure mimicking a part of an experimentally observed H-bridged polymeric chain. The Gibbs free deprotonation energy of the dimeric (H(CHB11 Cl11 ))2 acid was predicted to be smaller by 17 kcal/mol than that of the corresponding monomeric H(CHB11 Cl11 ) acid.

Formation of Enormously Strongly Bound Anionic Clusters Predicted in Binary Superacids.

The possible formation of the (AlF4(HF) n)- ( n = 1-8 and 12), (AsF6(HF) n)-, and (SbF6(HF) n)- ( n = 1-6 and 12) anionic clusters of a superhalogen nature is predicted in the solutions of binary HF/AlF3, HF/AsF5, and HF/SbF5 Lewis-Brønsted superacids on the basis of ab initio calculations. Our results show that all systems investigated represent extremely strongly bound anions characterized by vertical electron detachment energies (VDEs) that significantly exceed 10 eV. The VDE values estimated for the (AlF4(HF)12)-, (AsF6(HF)12)-, and (SbF6(HF)12)- systems are predicted to be 13.96, 14.03, and 14.03 eV, respectively, and are the largest vertical electron detachment energies reported in the literature thus far.

Dissociative electron attachment to HGaF4 Lewis-Brønsted superacid.

The consequences of an excess electron attachment to HGaF4 (HF/GaF3) superacid are investigated on the basis of theoretical calculations employing ab initio methods. It is found that the dipole potential of HGaF4 plays an important role in the initial formation of a dipole-bound anionic state. Due to the kinetic instability of that initially formed anion, a fragmentation reaction occurs promptly and leads to (GaF4)- and H as the final products. The energy profile of this process, its rate, and mechanism are presented and discussed.

Mechanisms of carbon monoxide hydrogenation yielding formaldehyde catalyzed by the representative strong mineral acid, H2SO4, and Lewis-Brønsted superacid, HF/AlF3.

The mechanism of the CO + H2→ H2CO reaction catalyzed by acidic systems was investigated theoretically using the ab initio MP2 and CCSD(T) methods and the aug-cc-pVDZ basis set (the effects of the surrounding solvent molecules were approximated by employing the polarized continuum solvation model). Two representative acids were chosen to verify the usefulness of such catalysts in this process: sulfuric acid (as a strong mineral acid) and HAlF4 (as a superacid). Detailed mechanisms in both gas and liquid phases proceeding either along a concerted path or according to a stepwise route were investigated and discussed. The most important findings include the observation that both acids seem to catalyze the carbon monoxide hydrogenation in a qualitatively similar way but only the HAlF4 superacid is predicted to effectively reduce the activation barriers to render the whole process plausible.

Strength of the Lewis-Brønsted Superacids Containing In, Sn, and Sb and the Electron Binding Energies of Their Corresponding Superhalogen Anions.

The HInnF3n+1, HSnnF4n+1, and HSbnF5n+1 (n = 1-3) compounds and their corresponding InnF3n+1(-), SnnF4n+1(-), SbnF5n+1(-) (n = 1-3) anions were investigated by employing the B3LYP, QCISD, and OVGF quantum chemistry methods and the LANL2DZ/6-311++G(d,p) basis sets. Our calculations revealed very strong acidity of all examined neutral compounds and large electronic stabilities (in the range 9.9-13.3 eV) of their corresponding anions. The gas phase acidities (manifested by small Gibbs free energies of deprotonation, ΔGacid) predicted for the HSn3F13 and HSb3F16 (ΔGacid of 243.5 and 230.3 kcal/mol at T = 298.15 K, respectively) suggest that these systems should actually act as even stronger acids than the F(SO3)4H and HSbF6 compounds (recognized thus far as the strongest superacids).

The HAlF4 superacid fragmentation induced by an excess electron attachment.

The excess electron attachment to the HAlF4 superacid molecule was studied by employing ab initio CCSD(T) and MP2 methods and a purposely suited aug-cc-pVTZ+4s4p3d basis set. The results indicate that the HAlF4 molecule, due to its polarity, may attract a distant excess electron and form a dipole-bound anionic state whose vertical electron binding energy is 1106 cm(-1). The initially formed (HAlF4)(-) anion of a dipole-bound nature undergoes an immediate structural reorganization driven by the (AlF4)(-) strongly-bound superhalogen anion formation. The potential energy surface analysis leads to the conclusion that the (HAlF4)(-) → (AlF4)(-) + H transformation should proceed spontaneously and involve the simultaneous structure relaxation of the AlF4 moiety (in the direction approaching a tetrahedral geometry) and the excess electron density migration from the area outside the molecular framework to the valence AlF4 region. The fragmentation of the HAlF4 superacid molecule is predicted to be the final effect of the excess electron attachment process. In addition, the important antenna role of the initially formed (HAlF4)(-) dipole-bound anionic state is discussed.