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 B
详细信息 查看全文
- 作者：William J. Leigh ; Thomas R. Owens ; Michael Bendikov ; Sanjio S. Zade ; Yitzhak Apeloig
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：August 23, 2006
- 年：2006
- 卷：128
- 期：33
- 页码：10772 - 10783
- 全文大小：391K
- 年卷期：v.128,no.33(August 23, 2006)
- ISSN：1520-5126
文摘
The stabilized silene 1,1-bis(trimethylsilyl)-2-adamantylidenesilane (4) has been generated byphotolysis of a novel trisilacyclobutane derivative in various solvents and studied directly by kinetic UVspectrophotometry. Silene 4 decays with second-order kinetics in degassed hexane solution at 23 
C (k/
= 8.6 × 10-6 cm s-1) due to head-to-head dimerization. It reacts rapidly with oxygen [k(25 C) 
3 × 105M-1 s-1] but ~10 orders of magnitude more slowly with methanol (MeOH) than other silenes that havebeen 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 ofsilene 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 theB3LYP/6-31G(d) and MP2/6-31G(d) levels of theory. Hydrogen-bonded complexes with monomeric anddimeric methanol, in which the Si=C bond plays the role of nucleophile, have been located computationallyfor all three silenes. Reaction pathways have been characterized for reaction of the three silenes withmonomeric and dimeric ROH and reveal significantly lower barriers for reaction with the dimeric form ofthe alcohol in each case. The calculations indicate that 5 should be ~40-fold less reactive toward dimericMeOH than 4, in excellent agreement with the ~50-fold difference in the experimental rate constants forreaction in hexane solution.
C (k/= 8.6 × 10-6 cm s-1) due to head-to-head dimerization. It reacts rapidly with oxygen [k(25 C) 3 × 105M-1 s-1] but ~10 orders of magnitude more slowly with methanol (MeOH) than other silenes that havebeen 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 ofsilene 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 theB3LYP/6-31G(d) and MP2/6-31G(d) levels of theory. Hydrogen-bonded complexes with monomeric anddimeric methanol, in which the Si=C bond plays the role of nucleophile, have been located computationallyfor all three silenes. Reaction pathways have been characterized for reaction of the three silenes withmonomeric and dimeric ROH and reveal significantly lower barriers for reaction with the dimeric form ofthe alcohol in each case. The calculations indicate that 5 should be ~40-fold less reactive toward dimericMeOH than 4, in excellent agreement with the ~50-fold difference in the experimental rate constants forreaction in hexane solution.