C_Ar–H···O Hydrogen Bonds in Substituted Isobenzofuranone Derivatives: Geometric, Topological, and NMR Characterization

Substituted isobenzofuranone derivatives <b>1a</b>–<b>3a</b> and bindone <b>4</b> are characterized by the presence of an intramolecular C_Ar–H···O hydrogen bond in the crystal (X-ray), solution (¹H NMR and specific and nonspecific IEF-PCM solvation model combined with MP2 and B3LYP methods), and gas (MP2 and B3LYP) phases. According to geometric and AIM criteria, the C_Ar–H···O interaction weakens in <b>1a</b>–<b>3a</b> (independent of substituent nature) and in <b>4</b> with the change in media in the following order: gas phase > CHCl₃ solution > DMSO solution > crystal. The maximum value of hydrogen bond energy is 4.6 kcal/mol for <b>1a</b>–<b>3a</b> and 5.6 kcal/mol for <b>4</b>. Both in crystals and in solutions, hydrogen bond strength increases in the order <b>1a</b> < <b>2a</b> < <b>3a</b> with the rising electronegativity of the ring substituents (H < OMe < Cl). The best method for calculating ¹H NMR chemical shifts (δ^calcd – δ^expl < 0.7 ppm) of hydrogen bonded and nonbonded protons in <b>1a</b>–<b>3a</b> and <b>1b</b>–<b>3b</b> (isomers without hydrogen bonds) is the GIAO method at the B3LYP level with the 6-31G** and 6-311G** basis sets. For the C–H moiety involved in the hydrogen bond, the increase of the spin–spin coupling constant ¹<i>J</i>(¹³C–¹H) by about 7.5 Hz is in good agreement with calculations for C–H bond shortening and for blue shifts of C–H stretching vibrations (by 55–75 cm^–1)

C_Ar–H···O Hydrogen Bonds in Substituted Isobenzofuranone Derivatives: Geometric, Topological, and NMR Characterization

Substituted isobenzofuranone derivatives <b>1a</b>–<b>3a</b> and bindone <b>4</b> are characterized by the presence of an intramolecular C_Ar–H···O hydrogen bond in the crystal (X-ray), solution (¹H NMR and specific and nonspecific IEF-PCM solvation model combined with MP2 and B3LYP methods), and gas (MP2 and B3LYP) phases. According to geometric and AIM criteria, the C_Ar–H···O interaction weakens in <b>1a</b>–<b>3a</b> (independent of substituent nature) and in <b>4</b> with the change in media in the following order: gas phase > CHCl₃ solution > DMSO solution > crystal. The maximum value of hydrogen bond energy is 4.6 kcal/mol for <b>1a</b>–<b>3a</b> and 5.6 kcal/mol for <b>4</b>. Both in crystals and in solutions, hydrogen bond strength increases in the order <b>1a</b> < <b>2a</b> < <b>3a</b> with the rising electronegativity of the ring substituents (H < OMe < Cl). The best method for calculating ¹H NMR chemical shifts (δ^calcd – δ^expl < 0.7 ppm) of hydrogen bonded and nonbonded protons in <b>1a</b>–<b>3a</b> and <b>1b</b>–<b>3b</b> (isomers without hydrogen bonds) is the GIAO method at the B3LYP level with the 6-31G** and 6-311G** basis sets. For the C–H moiety involved in the hydrogen bond, the increase of the spin–spin coupling constant ¹<i>J</i>(¹³C–¹H) by about 7.5 Hz is in good agreement with calculations for C–H bond shortening and for blue shifts of C–H stretching vibrations (by 55–75 cm^–1)

C_Ar–H···O Hydrogen Bonds in Substituted Isobenzofuranone Derivatives: Geometric, Topological, and NMR Characterization

Substituted isobenzofuranone derivatives <b>1a</b>–<b>3a</b> and bindone <b>4</b> are characterized by the presence of an intramolecular C_Ar–H···O hydrogen bond in the crystal (X-ray), solution (¹H NMR and specific and nonspecific IEF-PCM solvation model combined with MP2 and B3LYP methods), and gas (MP2 and B3LYP) phases. According to geometric and AIM criteria, the C_Ar–H···O interaction weakens in <b>1a</b>–<b>3a</b> (independent of substituent nature) and in <b>4</b> with the change in media in the following order: gas phase > CHCl₃ solution > DMSO solution > crystal. The maximum value of hydrogen bond energy is 4.6 kcal/mol for <b>1a</b>–<b>3a</b> and 5.6 kcal/mol for <b>4</b>. Both in crystals and in solutions, hydrogen bond strength increases in the order <b>1a</b> < <b>2a</b> < <b>3a</b> with the rising electronegativity of the ring substituents (H < OMe < Cl). The best method for calculating ¹H NMR chemical shifts (δ^calcd – δ^expl < 0.7 ppm) of hydrogen bonded and nonbonded protons in <b>1a</b>–<b>3a</b> and <b>1b</b>–<b>3b</b> (isomers without hydrogen bonds) is the GIAO method at the B3LYP level with the 6-31G** and 6-311G** basis sets. For the C–H moiety involved in the hydrogen bond, the increase of the spin–spin coupling constant ¹<i>J</i>(¹³C–¹H) by about 7.5 Hz is in good agreement with calculations for C–H bond shortening and for blue shifts of C–H stretching vibrations (by 55–75 cm^–1)

Cage Complexes of Carbenium and Silylium Cations with an Aromatic Base. Is the η⁶ Coordination Type Realizable?

The cage cations [E­((CH₂)₃)₃C₆R₃]⁺ (E = C (<b>1</b>), Si (<b>2</b>); R = H (<b>a</b>), Li (<b>b</b>), F (<b>c</b>)) were studied theoretically using the MP2/6-311++G­(d,p) approach. The migration of the electrophilic center E and a proton around the perimeter of the arene ring in the cations [E­((CH₂)₃)₃C₆H₃]⁺ was considered. Our results are indicative of the π type of E←arene coordination in the intramolecular complexes [E­((CH₂)₃)₃C₆R₃]⁺. The cation [Si­((CH₂)₃)₃C₆H₃]⁺ (<b>2a</b>), which corresponds to a peak (M – CH₃)⁺ at <i>m</i>/<i>z</i> 229 in the mass spectrum of methylsilacyclophane, exists in a firmly established η¹π form, as opposed to the case for the known complexes of the trivalent silicon atom with aromatic bases. The species [C­((CH₂)₃)₃C₆F₃]⁺ (<b>1c</b>), as well as <b>4a</b>, obtained by connecting the equatorial carbon atoms in [Si­((CH₂)₃)₃C₆H₃]⁺ by a methylene bridge, are the first representatives of stable “face” complexes of carbenium and silylium cations with a benzene ring. The process of deprotonation of the complexes [C­((CH₂)₃)₃C₆H₃]⁺, [Si­((CH₂)₃)₃C₆H₃]⁺, and <b>4a</b> was found to be energetically unfavorable, even in the presence of a strong base such as NEt₃. The effect of the counterions BX₄^– (X = F, C₆F₅) and the polarity of solvents on the structure of the above cations was investigated using the examples of toluene and DMSO

Molecular Design of Hypercoordinated Silacyclophanes

MP2 and DFT (B3LYP, M06-2X) methods using the 6-31G(d) and 6-311++G(d,p) basis sets are applied to the investigation of the structure of a wide series of silacyclophanes XSi[Y(CH₂)_<i>n</i>]₃C₆R₃ <b>1</b>–<b>9</b> (X = <i>t</i>-Bu, Me, NH₂, F, OTf; Y = O, NH, CH₂; R = H, SiH₃, Li; <i>n</i> = 1, 2). The molecules studied exist exclusively in the <i>out</i>-<i>C</i>₃-symmetric form (for X = NH₂, OTf the symmetry is not strict). Identification of the presence and estimation of the extent of the hitherto unknown Si···Ar multicenter intramolecular interaction of the tetracoordinate silicon atom with the π-system of the benzene ring in <b>1</b>–<b>9</b> was performed by analysis of geometric parameters, using the methods of Δδ ²⁹Si coordination shift, NICS(1) values, and the results of the AIM, NBO, and MO analyses. In molecules XSi[YCH₂CH₂]₃C₆R₃ <b>1</b>–<b>4</b>, irrespective of the nature of X, Y, and R, the multicenter interaction Si···Ar is weak. This interaction is strongly enhanced in compounds XSi[YCH₂]₃C₆R₃ <b>5</b>–<b>9</b>, with side chains shortened by one methylene group. The variation of geometric (<i>d</i>_Si–Ar, Δ_Si, η_α), electronic (∑δ(Si,C)), orbital (∑Δ<i>E</i>⁽²⁾[π_C–C→σ*_Si‑X]), and NMR (Δδ ²⁹Si) characteristics of the coordination center XSiY₃Ar in <b>5</b>–<b>9</b>, caused by varying the environments of the silicon atom and of the arene fragment, is typical for pentacoordinate silicon compounds

Dipole-Bound Anions of Intramolecular Complexes

Dipole-bound molecular anions are often envisioned as unperturbed neutral, polar molecules with single excess electrons. We report the observation of intramolecular structural distortions within silatrane molecules due to the formation of their dipole-bound anions. The combination of Rydberg electron transfer–anion photoelectron spectroscopy (RET-PES) and ab initio computational methodologies (CCSD and MP2) was used to study 1-hydro- (<b>HS</b>) and 1-fluoro- (<b>FS</b>) silatranes and their dipole bound anions, <b>HS</b>^<b>–</b> and <b>FS</b>^<b>–</b>. The vertical detachment energies (VDEs) of <b>HS</b>^<b>–</b> and <b>FS</b>^<b>–</b> were measured to be 48 and 93 meV, respectively. Ab initio calculations accurately reproduced these VDE values as well as their photoelectron spectral profiles. This work revealed significant shortening (by ∼0.1 Å) of dative Si ← N bond lengths when <b>HS</b> and <b>FS</b> formed dipole-bound anions, <b>HS</b>^<b>–</b> and <b>FS</b>^<b>–</b>. Detailed computational (Franck–Condon) analyses explained the absence of vibrational features in the photoelectron spectra of <b>HS</b>^<b>–</b> and <b>FS</b>^–