A combined experimental and theoretical study of the kinetics and mechanism of the addition of alcohols to electronically stabilized silenes: A new mechanism for the addition of alcohols to the Si=C bond

William J. Leigh, Thomas R. Owens, Michael Bendikov, Sanjio S. Zade, Yitzhak Apeloig

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

The stabilized silene 1,1-bis(trimethylsilyl)-2-adamantylidenesilane (4) has been generated by photolysis of a novel trisilacyclobutane derivative in various solvents and studied directly by kinetic UV spectrophotometry. Silene 4 decays with second-order kinetics in degassed hexane solution at 23 °C (k/ε = 8.6 × 10-6 cm s-1) due to head-to-head dimerization. It reacts rapidly with oxygen [k(25 °C) ≈ 3 × 10 5 M-1 s-1] but ∼10 orders of magnitude more slowly with methanol (MeOH) than other silenes that have been studied previously. The data are consistent with a mechanism involving reaction with the hydrogen-bonded dimer of the alcohol, (MeOH)2 (k = 40 ± 3 M-1 s-1; kH/kD = 1.7 ± 0.2). The stable analogue of silene 4,1-tert-butyldimethylsilyl-1-trimethylsilyl-2- adamantylidenesilane (5), reacts ∼50 times more slowly, but via the same mechanism. The mechanism for addition of water and methanol (ROH; R = H, Me) to 4, 5, and the model compound 1,1-bis(silyl)-2,2-dimethylsilene (3a) has been studied computationally at the B3LYP/6-31G(d) and MP2/6-31G(d) levels of theory. Hydrogen-bonded complexes with monomeric and dimeric methanol, in which the Si=C bond plays the role of nucleophile, have been located computationally for all three silenes. Reaction pathways have been characterized for reaction of the three silenes with monomeric and dimeric ROH and reveal significantly lower barriers for reaction with the dimeric form of the alcohol in each case. The calculations indicate that 5 should be ∼40-fold less reactive toward dimeric MeOH than 4, in excellent agreement with the ∼50-fold difference in the experimental rate constants for reaction in hexane solution.

Original languageEnglish
Pages (from-to)10772-10783
Number of pages12
JournalJournal of the American Chemical Society
Volume128
Issue number33
DOIs
Publication statusPublished - Aug 23 2006

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Silene
Methanol
Alcohols
Theoretical Models
Hexanes
Hexane
Hydrogen
Kinetics
Nucleophiles
Dimerization
Photolysis
Spectrophotometry
Dimers
Rate constants
Oxygen
Derivatives
Water

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

A combined experimental and theoretical study of the kinetics and mechanism of the addition of alcohols to electronically stabilized silenes : A new mechanism for the addition of alcohols to the Si=C bond. / Leigh, William J.; Owens, Thomas R.; Bendikov, Michael; Zade, Sanjio S.; Apeloig, Yitzhak.

In: Journal of the American Chemical Society, Vol. 128, No. 33, 23.08.2006, p. 10772-10783.

Research output: Contribution to journalArticle

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abstract = "The stabilized silene 1,1-bis(trimethylsilyl)-2-adamantylidenesilane (4) has been generated by photolysis of a novel trisilacyclobutane derivative in various solvents and studied directly by kinetic UV spectrophotometry. Silene 4 decays with second-order kinetics in degassed hexane solution at 23 °C (k/ε = 8.6 × 10-6 cm s-1) due to head-to-head dimerization. It reacts rapidly with oxygen [k(25 °C) ≈ 3 × 10 5 M-1 s-1] but ∼10 orders of magnitude more slowly with methanol (MeOH) than other silenes that have been studied previously. The data are consistent with a mechanism involving reaction with the hydrogen-bonded dimer of the alcohol, (MeOH)2 (k = 40 ± 3 M-1 s-1; kH/kD = 1.7 ± 0.2). The stable analogue of silene 4,1-tert-butyldimethylsilyl-1-trimethylsilyl-2- adamantylidenesilane (5), reacts ∼50 times more slowly, but via the same mechanism. The mechanism for addition of water and methanol (ROH; R = H, Me) to 4, 5, and the model compound 1,1-bis(silyl)-2,2-dimethylsilene (3a) has been studied computationally at the B3LYP/6-31G(d) and MP2/6-31G(d) levels of theory. Hydrogen-bonded complexes with monomeric and dimeric methanol, in which the Si=C bond plays the role of nucleophile, have been located computationally for all three silenes. Reaction pathways have been characterized for reaction of the three silenes with monomeric and dimeric ROH and reveal significantly lower barriers for reaction with the dimeric form of the alcohol in each case. The calculations indicate that 5 should be ∼40-fold less reactive toward dimeric MeOH than 4, in excellent agreement with the ∼50-fold difference in the experimental rate constants for reaction in hexane solution.",
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AU - Leigh, William J.

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AU - Zade, Sanjio S.

AU - Apeloig, Yitzhak

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N2 - The stabilized silene 1,1-bis(trimethylsilyl)-2-adamantylidenesilane (4) has been generated by photolysis of a novel trisilacyclobutane derivative in various solvents and studied directly by kinetic UV spectrophotometry. Silene 4 decays with second-order kinetics in degassed hexane solution at 23 °C (k/ε = 8.6 × 10-6 cm s-1) due to head-to-head dimerization. It reacts rapidly with oxygen [k(25 °C) ≈ 3 × 10 5 M-1 s-1] but ∼10 orders of magnitude more slowly with methanol (MeOH) than other silenes that have been studied previously. The data are consistent with a mechanism involving reaction with the hydrogen-bonded dimer of the alcohol, (MeOH)2 (k = 40 ± 3 M-1 s-1; kH/kD = 1.7 ± 0.2). The stable analogue of silene 4,1-tert-butyldimethylsilyl-1-trimethylsilyl-2- adamantylidenesilane (5), reacts ∼50 times more slowly, but via the same mechanism. The mechanism for addition of water and methanol (ROH; R = H, Me) to 4, 5, and the model compound 1,1-bis(silyl)-2,2-dimethylsilene (3a) has been studied computationally at the B3LYP/6-31G(d) and MP2/6-31G(d) levels of theory. Hydrogen-bonded complexes with monomeric and dimeric methanol, in which the Si=C bond plays the role of nucleophile, have been located computationally for all three silenes. Reaction pathways have been characterized for reaction of the three silenes with monomeric and dimeric ROH and reveal significantly lower barriers for reaction with the dimeric form of the alcohol in each case. The calculations indicate that 5 should be ∼40-fold less reactive toward dimeric MeOH than 4, in excellent agreement with the ∼50-fold difference in the experimental rate constants for reaction in hexane solution.

AB - The stabilized silene 1,1-bis(trimethylsilyl)-2-adamantylidenesilane (4) has been generated by photolysis of a novel trisilacyclobutane derivative in various solvents and studied directly by kinetic UV spectrophotometry. Silene 4 decays with second-order kinetics in degassed hexane solution at 23 °C (k/ε = 8.6 × 10-6 cm s-1) due to head-to-head dimerization. It reacts rapidly with oxygen [k(25 °C) ≈ 3 × 10 5 M-1 s-1] but ∼10 orders of magnitude more slowly with methanol (MeOH) than other silenes that have been studied previously. The data are consistent with a mechanism involving reaction with the hydrogen-bonded dimer of the alcohol, (MeOH)2 (k = 40 ± 3 M-1 s-1; kH/kD = 1.7 ± 0.2). The stable analogue of silene 4,1-tert-butyldimethylsilyl-1-trimethylsilyl-2- adamantylidenesilane (5), reacts ∼50 times more slowly, but via the same mechanism. The mechanism for addition of water and methanol (ROH; R = H, Me) to 4, 5, and the model compound 1,1-bis(silyl)-2,2-dimethylsilene (3a) has been studied computationally at the B3LYP/6-31G(d) and MP2/6-31G(d) levels of theory. Hydrogen-bonded complexes with monomeric and dimeric methanol, in which the Si=C bond plays the role of nucleophile, have been located computationally for all three silenes. Reaction pathways have been characterized for reaction of the three silenes with monomeric and dimeric ROH and reveal significantly lower barriers for reaction with the dimeric form of the alcohol in each case. The calculations indicate that 5 should be ∼40-fold less reactive toward dimeric MeOH than 4, in excellent agreement with the ∼50-fold difference in the experimental rate constants for reaction in hexane solution.

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