Fluoride ion induced rearrangements of chloromethyl-substituted silanes: carbanionic character of groups undergoing migration

Damrauer, Robert; Danahey, Stephen E.; Yost, Vernon E.

doi:10.1021/ja00336a060

Cited by 22 publications

(2 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Chloromethyl and bromomethyl anions (CH 2 X - , X = Cl, Br) were prepared by fluoride-induced desilylation of the corresponding halomethyltrimethylsilanes, as shown in eq 8. The major ionic product of both reactions is the corresponding halide ion, Cl - and Br - , formed either by nucleophilic displacement at carbon or by a dissociative rearrangement involving attack at silicon followed by methyl migration …”

Section: Resultsmentioning

confidence: 99%

Absolute Heats of Formation of Phenylcarbene and Vinylcarbene

et al. 1997

View full text Add to dashboard Cite

The method of collision-induced dissociation threshold analysis for determining carbene thermochemistry is applied to the ground-state triplet carbenes CH2 (methylene, 1), CH2CHCH (vinylcarbene, 2), and PhCH (phenylcarbene, 3). The chief aims of this study are to evaluate the energetic and dynamical consequences of the obligatory curve-crossing that characterizes dissociation of a halide ion from an α-halocarbanion to form a carbene with a triplet ground state, and to determine accurate heats of formation for 2 and 3. Threshold collision energies for loss of halide from CH2X- (X = Cl, Br), CH2CHCHX- (X = Cl, Br, I), and PhCHX- (X = Cl, Br, I) are determined with use of a flowing afterglow−triple quadrupole apparatus. The dissociation energies are combined with the measured gas-phase acidities of the corresponding methyl, allyl, and benzyl halides in simple thermochemical cycles in order to derive the absolute heats of formation for the carbenes. The value of ΔH f,298(1) derived from the results for the two different methyl halides (92.2 ± 3.7 kcal/mol) is in excellent agreement with the well-established literature value for the triplet ground state of methylene: ΔH f,298[X̃ 3B1 CH2] = 92.9 ± 0.6 kcal/mol. The good agreement indicates that dissociation of the halomethyl anions occurs adiabatically to produce the triplet state of the product without any significant reverse activation energy or dynamical constraints. The measured dissociation energies for 1-chloro-, 1-bromo-, and 1-iodoallyl anions are combined with the bracketed acidities of allyl chloride, bromide, and iodide to yield three independently determined but closely matched values for ΔH f,298(2): 92.3 ± 2.6, 93.9 ± 3.4, and 93.2 ± 3.1 kcal/mol, respectively. The average value from the three determinations, 93.3 ± 3.4 kcal/mol, is in fair agreement with the estimated heat of formation for the triplet ground state of 2 obtained from various MCSCF and density functional calculations (90 kcal/mol), but much lower than the predicted heat of formation for the lowest singlet state of 2 (100 kcal/mol). As with the halomethyl ions, efficient adiabatic dissociation of the haloallyl anions at the thermodynamic limit is indicated by these results. The apparent heats of formation for 3 derived from the measured dissociation energies for PhCHCl-, PhCHBr- and PhCHI-, and the bracketed acidities of the corresponding benzyl halides show a somewhat larger (non-systematic) variation, but are all within the assigned uncertainties. The derived values for ΔH f,298(3) are 103.2 ± 3.2, 105.5 ± 2.7, and 100.9 ± 2.8 kcal/mol for the benzyl chloride, bromide, and iodide systems, respectively, giving an average value of 102.8 ± 3.5 kcal/mol. The measured heats of formation for 2 and 3 are compared with the predictions obtained from various levels of ab initio theory. Density functional calculations with the BVWN5 and B3LYP functionals in conjunction with polarized, triple-ζ basis sets are found to perform best with respect to the singlet−triplet splittings and absolute heats o...

show abstract

Section: Resultsmentioning

confidence: 99%

Absolute Heats of Formation of Phenylcarbene and Vinylcarbene

et al. 1997

View full text Add to dashboard Cite

show abstract

“…Damrauer's studies of rearrangements of chloromethyl trialkylsilanes (R 3 SiCH 2 Cl) showed dependence on fluoride ion, consistent with formation of a pentavalent intermediate. 12 Sakurai has effected conversion of trifluorosilanes to alcohols with trimethylamine-N-oxide, and proposed that the reaction occurs via a pentacoordinate silane by attack of oxygen on silicon followed by migration of an alkyl group from silicon. In this case, an excess of fluoride was not required.…”

Section: Introductionmentioning

confidence: 99%

Quantum Chemical Investigation of Mechanisms of Silane Oxidation

Mader

Norrby

2001

J. Am. Chem. Soc.

View full text Add to dashboard Cite

Several mechanisms for the peroxide oxidation of organosilanes to alcohols are compared by quantum chemical calculations, including solvation with the PCM method. Without doubt, the reaction proceeds via anionic, pentacoordinate silicate species, but a profound difference is found between in vacuo and solvated reaction profiles, as expected. In the solvents investigated (CH(2)Cl(2) and MeOH), the most favorable mechanism is addition of peroxide anion to a fluorosilane (starting material or formed in situ), followed by a concerted migration and dissociation of hydroxide anion. In the gas phase, and possibly in very nonpolar solvents, concerted addition-migration of H(2)O(2) to a pentacoordinate fluorosilicate is also plausible.

show abstract

18-Crown-6

Charles

Berkner

2001

Encyclopedia of Reagents for Organic Synthesis

View full text Add to dashboard Cite

Fluoride ion induced rearrangements of chloromethyl-substituted silanes: carbanionic character of groups undergoing migration

Cited by 22 publications

References 3 publications

Absolute Heats of Formation of Phenylcarbene and Vinylcarbene

Absolute Heats of Formation of Phenylcarbene and Vinylcarbene

Quantum Chemical Investigation of Mechanisms of Silane Oxidation

18-Crown-6

Contact Info

Product

Resources

About