Synthesis, Structures, and Stereodynamic Behavior of Novel Pentacoordinate Fluorosilanes: Fluorosilyl Derivatives of Proline

Abstract

were synthesized from the corresponding disiloxanes 1a−f using Et 2 O•BF 3 . According to the NMR and IR data, the extent of dimerization of fluorosilanes 2a−f in solution is negligible, while the O→Si coordination in solution is weaker than that in the solid state. Comparative CP/MAS NMR and X-ray diffraction studies revealed that in solution the coordination Si−O bond length varies in a narrow range (2.22−2.24 Å) that is 0.02−0.11 Å longer than in the crystalline state. Dynamic NMR (DNMR) studies of the fluorides revealed a fine structure of the 19 F signals in the 0−20 °C temperature range, which was related to the structural features of the coordination set in these complexes. The temperature dependence of the SiMe 2 signals in the 1 H DNMR spectra was attributed to a permutational isomerization process involving a positional exchange of equatorial ligands. The narrow range of activational barriers of the process (23−24 kcal mol −1 and more) and high negative values of the entropy of activation are similar to those observed earlier for Si-substituted N-(dimethylsilylmethyl) and N-(methylphenylsilylmethyl) amides and lactams, which suggests similar permutational processes in all cases. Gas-phase quantum chemical studies demonstrate that the solvation of F − reduces the activation barrier.

Intramolecular charge transfer and sensing mechanism for a colorimetric fluoride sensor based on 1,8-naphthalimide derivatives

“…1, the calculated Si-O bond length is 1.72 Å in TBS-NA. With the addition of the fluoride anion, the Si-O bond is broken and a new F-Si bond is formed, which is verified by that the calculated distance of Si-O is 5.05 Å and the F-Si bond distance is 1.67 Å in TBS-NAF [29]. To further elucidate the role of the fluoride-triggered Si-O bond cleavage process in the fluoride-sensing mechanism of TBS-NA, the profile of free energy in solution was computed for the desilylation process (see Fig.…”

Chelation and Stereodynamic Equilibria in Neutral Hypercoordinate Organosilicon Complexes of 1-Hydroxy-2-pyridinone

“…Si−O bond length has been observed previously for a series of prolinamide complexes. 10,39 The relative strengths of the Si←OC interaction in solution are therefore indicated in the order i Pr < Et < Me < (CH2)3 < Ph. Further support for OPO chelation equilibria is given by was obtained by VT-NMR studies.…”

“…One class of these complexes possesses chelate ring(s) with hemilabile ligand(s) which bear one inert and one labile heteroatom donor. Examples of neutral complexes of this type exhibiting dynamic Si←N or Si←O dative bond rupture include those based on N , N -dimethylbenzylamine, tropolone, acetylacetone, quinolone, salicylaldimine, hydrazide, acetamide, prolinamide, and glutarimide ligands, among many others. These complexes are fundamentally interesting with respect to dynamic changes in their coordination mode, with their dative interactions often being strongly influenced by solvent, temperature, and substituent effects.…”

Sensing mechanism for a fluoride chemosensor: invalidity of excited-state proton transfer mechanism

“…This result indicates that the Si-O bond was broken, and a new F-Si bond was formed with the addition of the fluoride anion. 45 Given the high chemical affinity between fluoride and silicon, silyl ether protecting groups were removed by the added fluoride anion. 12 To understand the aforementioned desilylation reaction mechanism, the PES of the S 0 state of the chemosensor DBM as a function of the FÁ Á ÁSi distance from 5.00 Å to 1.60 Å in steps of 0.1 Å was constructed [see Fig.…”