Formation and Decomposition of Hydroxysiliconates in the Gas Phase

Abstract

Supplemental Figure S1, mass spectra of the reaction of OH − (H 2 O) n with FSi(CH 3 ) 3 for n = 1 -3 (a -c, respectively). Scheme S1, computations for conformations of 1, 2 and 3A. Tables S1 -S3.Listings of B3LYP/6-31+G* geometries, unscaled frequencies, Mulliken charges, absolute energies and 298 K enthalpies for structures A, B, C, AB, and AC for 1, 2, and 3. Tables S4 -S22.Listings of B3LYP/aug-cc-pVDZ, B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ geometries, unscaled frequencies, absolute energies and 298 K enthalpies for structures 1A, 1AB and 1B. Single point energies for B3LYP/6-31+G*, B3LYP/aug-cc-pVDZ. B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ structures of 1A, 1AB and 1B at different levels of theory. Tables S23 -S36.Listings of B3LYP/6-31+G* geometries, unscaled frequencies, absolute energies and 298 K enthalpies for all other relevant species, including neutrals and anions. Tables S37 -S75.

Fluorotrimethylsilane affinities of anionic nucleophiles: A study of fluoride-induced desilylation

“…SA(R Ϫ ) ϭ 0.36(⌬H acid,298 (RH)) Ϫ 105.6 (in kcal ⁄ mol) (5) For example, given the acidity of water (390.3 kcal/ mol) [77], the silane affinity of OH Ϫ is predicted to be ϳ35 kcal/mol, which agrees with the lower limit of 27 kcal/mol established from the reactivity of solvated OH Ϫ with FSi(CH 3 ) 3 [28]. On the other hand, using this relationship, the acidity of HF (371.3 kcal/mol) [77] suggests a fluoride affinity of 28 kcal/mol for FSi(CH 3 ) 3 , well below the experimental value of 38 kcal/mol (or higher) [43].…”

“…Changing the source conditions does not affect the branching ratios for the dissociation, suggesting (al-though not requiring) that they do not originate from a discrete ion mixture. However, we have recently shown [28] that the transition states for channels originating from double-well potentials reflect the exit channel properties when the barrier that separates the minima is much lower than the dissociation energy [73,74], such that the dissociation appears to be arising from distinct reactants. Computational evidence supporting the double-well potential picture is presented in the next section.…”

“…However, because third row and lower main-group elements (e.g., P, S, Cl) readily undergo hypervalent bonding [24], the pentavalent siliconate is a stable intermediate in the reaction and can, in many cases, be observed [25][26][27][28]. Because of their stability, siliconates are often used in fundamental studies of hypervalency [26, 29 -32], as well as in numerous theoretical [33,34] and experimental [7,29,[35][36][37][38][39][40] studies.…”

“…In continuation of our interest in inorganic main group gas-phase chemistry [27,28], we have studied the formation and decomposition of a series of pentavalent fluorosiliconates, RSi(CH 3 ) 3 F Ϫ . Although there has been some thermochemical characterization of pentavalent siliconates, the effects of substitution are not well known [41].…”

“…Chloride and fluoride affinities have been reported for some silanes [42][43][44], but there are few other experimental nucleophilic affinities. Most negative ion studies of silanes have focused upon reactivity [45][46][47][48][49] with few studies looking specifically at siliconrelated ion thermochemistry [27,28,43,50].…”