Comprehensive Insight into the Hydrogen Bonding of Silanes

Abstract

The interaction of a set of mono-, di- and trisubstituted silanes with OH proton donors of different strength was studied by variable temperature (VT) FTIR and NMR spectroscopies at 190-298 K. Two competing sites of proton donors coordination: SiH and π-density of phenyl rings-are revealed for phenyl-containing silanes. The hydrogen bonds SiH⋅⋅⋅HO and OH⋅⋅⋅π(Ph) are of similar strength, but can be distinguished in the ν range: the ν vibrations appear at lower frequencies while OH⋅⋅⋅π(Ph) complexes give Si-H vibrations shifted to higher frequency. The calculations showed the manifold picture of the noncovalent interactions in hydrogen-bonded complexes of phenylsilanes. As OH⋅⋅⋅HSi bonds are weak, the other noncovalent interactions compete in the stabilization of the intermolecular complexes. Still, the structural and electronic parameters of "pure" DHB complexes of phenylsilanes are similar to those of Et SiH.

Dichotomous Si–H Bond Activation by Alkoxide and Alcohol in Base-Catalyzed Dehydrocoupling of Silanes

“…Calculations of the Reaction Mechanism. As was shown in our previous work, 36 the interaction of phenylsilanes with alcohols in nonpolar aprotic solvents (such as n-hexane or toluene) causes the formation of the noncovalent (di)hydrogenbonded complexes and does not lead to H 2 release at ambient temperature. However, as we have shown experimentally, the formation of pentacoordinate complexes triggers this reaction.…”

“…The interaction of phenylsilanes (Ph 2 SiH 2 and PhSiH 3 ) with hexafluoro-2-propanol (HFIP; HOR = HOCH-(CF 3 ) 2 ) in low-polar solvents (n-hexane, toluene, THF, C 6 H 5 F) leads to the formation of a Si−H•••H−O dihydrogen bond, but no reaction was observed. 36 The addition of Et 3 N to this system leads to vigorous H 2 release. At equimolar reagents ratio Ph 2 SiH 2 /Et 3 N/HFIP (c = 0.05 M), the reaction in n-hexane proceeds only by 49% in 2 h as follows from the intensity decrease of the ν SiH band of initial compound (Figure S1).…”

“…These calculations are in accord with the experimental data, showing that the interaction of phenylsilanes with alcohols in aprotic nonpolar solvents (such as toluene, nhexane) does not lead to H 2 release. 36 At the same time, the Lewis acidity of Si atom characterized by maxima of molecular electrostatic potential (MEP), V S,max , which can be used as a quantitative descriptor of σ-hole, 81 varies from 16.0 (PhSiH 3 ) to 1.4 kcal/mol (Ph 3 SiH) (Table 1). This allows the formation of weak tetrel complexes with nucleophiles.…”

“…According to DFT calculations, coordination of RO − leads to the elongation of Si−H bond, the decrease of its bond order and s-character, 78,87,88 while the Si−H bond polarization adopts more hydridic character (Tables S4 S7). 36 All these changes facilitate the concerted proton−hydride transfer via DHB complex for which rather low barriers are found (ΔG ‡ Hex = 5.9−8.4 kcal/mol, TS C −OR , Table 3 and Figure 13).…”

The Partner Does Matter: The Structure of Heteroaggregates of Acridine Orange in Water

“…No intermolecular contacts were detected in test experiments for aqueous solutions of AOHCl with quinoline-HCl and N,N -dimethylpyridin-4-amine-HCl. Dipole-dipole NMR is quite sensitive to intermolecular interactions [36,37]. Therefore, only protonated acridines form in water relatively stable aggregates.…”