Substituent effects on the reactivity of the silicon–carbon double bond. Arrhenius parameters for the reaction of 1,1 -diarylsilenes with alcohols and acetic acid

Bradaric, Christine J.; Leigh, William J.

doi:10.1139/v97-167

Cited by 33 publications

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“…18,20,21 The two silenes exhibit lifetimes of >5 µs in hexane and 1-4 µs in acetonitrile under these conditions and decay with mixed firstand second-order kinetics, with 1a being the longer-lived of the two. Much different behavior is observed in THF solution, where the lifetimes of the two silenes are longer, 1b is the longer-lived of the two, and their spectra are broadened and/or red-shifted as compared to hexane solution because of complexation with the ether solvent.…”

Section: Resultsmentioning

confidence: 95%

“…This behavior is also analogous to what has been observed previously for the addition of oxygen-centered nucleophiles to these two silenes. 15,18,21 In the case of oxygen-centered nucleophiles, we have recently shown that these trends are due, at least to some extent, to the effects of weak complexation of the free silene…”

Section: Discussionmentioning

confidence: 99%

“…The 1,1-diarylsilacyclobutanes (4a,b) were prepared according to the published methods. 18 Steady state photolysis (254 nm) of deoxygenated 0.02-0.08 M solutions of the 1,1-diarylsilacyclobutanes 4a,b (10-20 mg) in hexane or cyclohexane-d 12 containing a ca. 10% molar excess of n-BuNH 2 , t-BuNH 2 , or Et 2 NH was carried out using a Rayonet photochemical reactor.…”

Section: Methodsmentioning

confidence: 99%

“…14,16,17 However, most of the transient silenes that have been studied to date are sufficiently reactive toward alcohols and water that only the second-order reaction pathway can be detected by these methods. 9 The 1,1-diarylsilene derivatives 1a-e are examples of silenes that show such behavior and have proven extremely useful in delineating the quantitative aspects of silene reactivity toward alcohols 18,19 and various other oxygen-centered nucleophiles. 9 The reaction of silenes with nitrogen-centered nucleophiles is also well-known, 1,3,8 but no detailed absolute kinetic studies have yet been reported.…”

Section: Introductionmentioning

confidence: 99%

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Kinetics and Mechanism of the Addition of Aliphatic Amines to Transient Silenes

Leigh

2003

J. Phys. Chem. A

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Primary and secondary amines such as n- butyl-, t-butyl-, and N,N-diethylamine add across the SidC bond of transient silenes such as 1,1-diphenylsilene (1a) and 1,1-bis(4-trifluoromethylphenyl)silene (1b) to yield the corresponding amino(methyl)diarylsilanes as the only products of reaction. The kinetics and mechanism of reaction of these three amines with the two 1,1-diarylsilene derivatives have been studied in hexane, acetonitrile, and tetrahydrofuran (THF) solution by laser flash photolysis techniques, using the corresponding 1,1-diarylsilacyclobutanes as photochemical precursors to the silenes. The reactions proceed with clean secondorder kinetics and bimolecular rate constants in excess of 5 × 10 8 M -1 s -1 in hexane and MeCN, with 1b being up to four times more reactive than 1a. Arrhenius plots for reaction in hexane and/or acetonitrile solution show strong curvature over the 0-60°C temperature range, consistent with an addition mechanism involving the intermediacy of a zwitterionic silene-amine addition complex, which collapses to product by intramolecular proton transfer from nitrogen to the silenic carbon. The reactions are substantially slower in THF, where rate reductions on the order of 5-10-fold and 50-70-fold are observed for 1a and 1b, respectively, as compared to MeCN solution. This is due to the effects of complexation of the silenes with the ether solvent, the equilibrium constant for which enters the expression for the reaction rate constant in the complexing solvent. In contrast to the situation in hexane and MeCN, Arrhenius plots for reaction of n-BuNH 2 with 1a,b in THF solution are linear and lead to positive activation energies. Addition of amines in THF solution is proposed to occur predominantly via the free silenes but with minor contributions from a pathway involving nucleophilic displacement of the solvent from the silene-solvent complex.

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Section: Resultsmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Kinetics and Mechanism of the Addition of Aliphatic Amines to Transient Silenes

Leigh

2003

J. Phys. Chem. A

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“…Nanosecond laser flash photolysis (NLFP) experiments employed a pulsed excimer laser filled with N 2 -He (337 nm, 4 mJ, 6 ns), Xe-HCl-He (308 nm, 55 mJ, 15 ns), or Kr-F 2 -N (248 nm, 100 mJ, 25 ns) for excitation, and a microcomputer-controlled detection system (19). Sample concentrations were such that the absorbance at the excitation wavelength (3-or 7-mm path length) was 0.2-0.9 and each sample was deoxygenated with argon or dry nitrogen until constant transient lifetimes were obtained.…”

Section: Resultsmentioning

confidence: 99%

Geometric and solvent effects on intramolecular phenolic hydrogen abstraction by carbonyl n,π* and π,π* triplets

Lathioor¹,

Leigh²

2001

Can. J. Chem.

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The photochemistry of a series of alkoxyacetophenone, -benzophenone, and -indanone derivatives, which contain a remote phenolic group linked to the ketone by a para,para¢-or meta,meta¢-oxyethyl spacer, has been studied in acetonitrile and dichloromethane solutions using laser flash photolysis techniques. The corresponding methoxysubstituted compounds and, in the case of the alkoxyindanones, derivatives bearing just a remote phenyl substituent, have also been examined. The triplet lifetimes of the phenolic compounds are determined by the rates of intramolecular abstraction of the remote phenolic hydrogen, and depend on the solvent, the geometry of attachment and the configuration of the lowest triplet state. In contrast to the large (>500-fold) difference in lifetime of the para,para¢-and meta,meta¢-alkoxyacetophenone derivatives, both of which have lowest p,p* triplet states, smaller differences are observed for the alkoxyindanone (lowest charge transfer triplet,~twofold difference) and alkoxybenzophenone (lowest n,p* triplet,~18-fold difference) derivatives in acetonitrile solution. The triplet lifetimes of the acetophenone and benzophenone are significantly shorter in dichloromethane than in acetonitrile, consistent with the intermediacy of a hydrogen-bonded triplet exciplex in the reaction. This is not the case with the para,para¢-indanone derivative, sugesting that hydrogen abstraction in this compound is dominated by a mechanism involving initial charge transfer rather than hydrogen bonding. This is most likely due to orientational constraints that prevent the remote phenolic -O-H group from adopting a coplanar arrangement with the n-orbitals of the carbonyl group.Résumé : Faisant appel à des techniques de photolyse éclair au laser et opérant dans des solutions d'acétonitrile et de dichlorométhane, on a étudié la photochimie d'une série de dérivés alkoxyacétophénones, -benzophénones et -indanones comportant un groupe phénolique dans une position éloignée, mais liée à la cétone par un espaceur oxyéthyle en para,para¢-ou méta,méta¢-. On a aussi étudié les composés correspondants portant des substituants méthoxy ainsi que, dans le cas des alkoxyindanones, des dérivés ne portant qu'un substituant phényle en position éloignée. On a déterminé les temps de vie du triplet des composés phénoliques à partir des vitesses d'enlèvement intramoléculaire de l'hydrogène phénolique éloigné; ils dépendent du solvant, de la géométrie de fixation et de la configuration de l'état triplet le plus bas. Par opposition à la grande différence (>500 fois) dans les temps de vie des dérivés para,para¢-et méta,méta¢-alkoxyacétophénones qui ont tous les deux des états triplets p,p* plus faibles, on observe des différences plus faibles pour les dérivés alkoxyindanones (triplet de transfert de charge le plus faible; différence du simple au double) et alkoxybenzophénones (triplet n,p* le plus faible; différence correspondant à une réaction environ 18 fois plus rapide) dans une solution d'acétonitrile. Les temps de vie des dérivés de l'acétop...

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Mechanism and Structures in Alcohol Addition Reactions of Disilenes and Silenes

Sakurai

2009

Patai's Chemistry of Functional Groups

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Substituent effects on the reactivity of the silicon–carbon double bond. Arrhenius parameters for the reaction of 1,1 -diarylsilenes with alcohols and acetic acid

Cited by 33 publications

References 0 publications

Kinetics and Mechanism of the Addition of Aliphatic Amines to Transient Silenes

Kinetics and Mechanism of the Addition of Aliphatic Amines to Transient Silenes

Geometric and solvent effects on intramolecular phenolic hydrogen abstraction by carbonyl n,π* and π,π* triplets

Mechanism and Structures in Alcohol Addition Reactions of Disilenes and Silenes

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