Computational Investigation of the Role of Fluoride in Tamao Oxidations

Abstract

The spin‐crossover complex [Fe(teec)6](ClO4)2 (teec = chloroethyltetrazole) exhibits a 50 % incomplete spin crossover in the temperature range 300–30 K. Time‐resolved synchrotron powder diffraction experiments have been carried out to elucidate its structural behavior. We report crystal structure models of this material at 300 K (high spin) and 90 K (low spin), as solved from synchrotron powder diffraction data by using Genetic Algorithm and Parallel Tempering techniques and refined with Rietveld refinement. During short synchrotron powder diffraction experiments (five minutes duration) two distinguishable lattices were observed the quantities of which vary with temperature. The implication of this phenomenon, that is interpreted as a structural phase transition associated with the high‐to‐low spin crossover, and the structural characteristics of the high‐spin and low‐spin models are discussed in relation to other compounds showing a similar type of spin‐crossover behavior.

Mechanistic Study of Arylsilane Oxidation through 19F NMR Spectroscopy

“…Figure 4b), and the rapid establishment of this equilibrium is to the detriment of methoxysilane oxidation. 8,9 The culmination of these effects is that fluoride-free and fluoride-promoted methoxysilane oxidations proceed at similar overall rates, but by different compositions of intermediates.…”

“…Arylsilanes are highly versatile intermediates in organic synthesis, with a number of methods having recently been disclosed for both their preparation and transformations . Among these, the oxidation of arylsilanes to phenols is relatively underexploited compared to the equivalent conversion of alkyl and alkenylsilanes into aliphatic alcohols and ketones, respectively, , and has only recently been developed as an efficient and general methodology. , Despite the demonstrated synthetic utility of this oxidation, , mechanistic explorations of this phenol synthesis are limited to a study of arylfluorosilane oxidation by Tamao and co-workers, and theoretical investigations on the oxidation of alkylfluorosilanes, and alkylalkoxysilanes (and mixed alkoxyfluorosilane derivatives) by Mader and Norrby. Here we describe an experimental study of the mechanism of the H 2 O 2 -mediated oxidation of arylalkoxysilanes, a reaction that proceeds in the presence or absence ,, of fluoride.…”

“…Mader and Norrby subsequently calculated (Scheme b) that anionic substitution of anionic pentavalent silicates (e.g., 6 ) is rapid, and that hydroperoxide anion is more likely to attack pentacoordinate silicon ( 6 ) than the neutral species ( 7 ). , They also proposed that addition of fluoride ions is not essential for the oxidation to proceed, but increases the rate of hydroperoxide attack at silicon via formation of a greater proportion of pentavalent trifluorosiliconate species, which are more reactive toward substitution of F – by HOO – than neutral tetravalent difluorosilanes. Importantly, these authors concluded that alkyl migration from conformer 8b , and not peroxide ion attack to generate hexacoordinate species such as 3 or 4 , is the rate-limiting step.…”

Exhaustively Trichlorosilylated C1 and C2 Building Blocks: Beyond the Müller–Rochow Direct Process

“…The aptitude of moieties C–SiX 3 to expand their coordination spheres and the more polarized C–Si bonds in adducts [C–SiX 3 L] n − ( n = 0, 1) are widely exploited in protecting group chemistry, Tamao oxidations, − and Hiyama-type C–C-coupling reactions. − The Peterson olefination benefits from both the α acidity and the Lewis acidity of alkylsilanes . Common to all of these examples is that the silyl groups do not appear in the final products, but are split off in the course of the transformations.…”

Mechanism and Selectivity of Methyl and Phenyl Migrations in Hypervalent Silylated Iminoquinones

“…However, it is now widely recognized that the formation of hypervalent silicon species, typically by the addition of strong silicophilic Lewis bases such as fluoride, greatly enhances the reactivity of alkyl-, alkenyl-, and arylsilanes . Because organosilanes are inexpensive, nontoxic, and readily handled, this strategy has been broadly used in reactions to form carbon–carbon and carbon–oxygen bonds.…”