THE b-SILICON EFFECT ON SOLVOLYSIS RATES
to a personal computer we followed the solvolyses in a
thermostatted bath controlled within Æ0.01 8C by taking at least
100 readings at appropriate intervals during 2.5 half-lives, and an
infinity reading after 10 half-lives of reaction. The experimental
errors in respective runs were generally less than 1.0% and the
reproducibility of the rate constants was within Æ1.5%.
Computational methods
The geometry of the compounds was fully optimized by using
the Gaussian 98 software package[19] at the DFT(B3LYP)/6-31G(d)
level of theory. All structures were characterized as energy
minima by calculation of the harmonic vibration frequencies,
using analytical second derivatives. No imaginary frequency was
obtained for all cations. Cartesian coordinates for the optimized
structures are listed in Table S7 of the Supporting Information.
Product analysis
Product analysis for the solvolysis of 1-tert-butyl-2-
(dimethylphenylsilyl)ethyl trifluoroacetate under the buffered
condition with 2,6-lutidine in the deuterated solvents was carried
out using 1H NMR spectrometry similarly as described before.[8,9]
A solution (0.1 M) of the 1-tert-butyl-2-(dimethylphenylsilyl)ethyl
trifluoroacetate in the presence of 1.5 equiv of 2,6-lutidine in
deuterated ethanol (CD3CD2OD) was allowed to react at 55 8C in a
fused NMR tube and the solvolysis products at ten half-lives were
identified by the 1H NMR spectra, providing the exclusive
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[5] M. A. Cook, C. Eaborn, D. R. M. Walton, J. Organometal. Chem. 1970,
24, 301–306.
—
formation (95%) of CH2 CHC(CH ) and C H Si(CH ) OCD CD
3
—
3 3
6
5
3 2
2
[6] For comprehensive review, see: J. B. Lambert, Tetrahedron 1990, 46,
2677–2689.
[7] J. B. Lambert, Y. Zhao, R. W. Emblidge, L. A. Salvador, X. Liu, J.-H. So, E.
C. Chelius, Acc. Chem. Res. 1999, 32, 183–190.
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Bull. Chem. Soc. Jpn 2006, 79, 1091–1099.
with the minor (5%) of trans-(1-dimethylphenylsilyl)-2-tert-
butylethylene. The characteristic peaks of respective products
in CD3CD2OD are as follows: 3,3-dimethyl-1-butene: 1H NMR d
1.00 (9H, s, t-Bu), 4.81 (1H, dd, J ¼ 10.7, 1.5 Hz), 4.90 (1H, dd,
J ¼ 17.5, 1.5 Hz), 5.82 (1H, dd, J ¼ 10.7, 17.5 Hz) and dimethyl-
phenylsilyl ethyl-d5 ether: 1H NMR d 0.34 (6H, s, SiCH3), 7.33–7.55
(5H, m, Ph-H). trans-(1-Dimethylphenylsilyl)-2-tert-butylethylene;
1H NMR d 0.29 and 0.33 (6H, s, SiCH3), 1.02 (9H, s, t-Bu), 5.67 (1H, d,
J ¼ 18.8 Hz), 6.14 (1H, d, J ¼ 18.8 Hz).
[10] Y. Yukawa, Y. Tsuno, Bull. Chem. Soc. Jpn 1959, 32, 971–981.
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[12] Y. Tsuno, M. Fujio, Chem. Soc. Rev. 1996, 25, 129–139.
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[14] E. Grunwald, S. Winstein, J. Am. Chem. Soc. 1948, 70, 846–854.
[15] F. L. Schadt, T. W. Bentley, P. v. R. Schleyer, J. Am. Chem. Soc. 1976, 98,
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[16] T. W. Bentley, G. E. Carter, J. Am. Chem. Soc. 1982, 104, 5741–5747.
[17] T. W. Bentley, G. Llewellyn, Prog. Phys. Org. Chem. 1990, 17, 121.
[18] The reaction constant parameters rX and the reactivities for 3
(Y¼p-MeO, H and m-CF3) are calibrated to the values at 50 8C in 60E.
[19] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, V. G. Zakrzewski, J. A. Montgomery, Jr, R. E. Stratmann, J.
C. Burant, S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin, M. C.
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Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski,
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Head-Gordon, E. S. Replogle, J. A. Pople, Gaussian 98, Revision A.11,
Gaussian, Inc.: Pittsburgh, PA, 2002.
Product analyses for solvolysis of 2-(dimethylphenylsilyl)-
1-methylethyl esters under the buffered condition with
2,6-lutidine in the deuterated solvent were carried out using
1H NMR spectrometry.
A
solution (9.6 Â 10ꢀ2 M) of the
trifluoroacetate or 3,5-dinitrobenzoate buffered with 1.5
equivalent of 2,6-lutidine in deuterated ethanol was allowed
to react at 55 8C for the trifluoroacetate and at 75 8C for
the 3,5-dinitrobenzoate, and the solvolysis products at ten
—
half-lives
were
identified
as
CH2 CHCH
and
—
3
C6H5Si(CH3)2CH2CH(CH3)OCD2CD3 (1:0.60 for OTFA and 1:0.69
for ODNBz); propylene: 1H NMR d 1.69 (3H, d, J ¼ 6.6 Hz, CH3), 4.89
(1H, d, J ¼ 10.0 Hz, CH2), 4.98 (1H, d, J ¼ 16.9 Hz, CH2), 5.74–5.83
(1H, m, CH) and (2-ethoxypropyl) dimethylphenylsilane: 1H NMR d
0.28 and 0.31 (6H, ss, SiCH3), 0.97 (1H, dd, J ¼ 14.6, 6.6 Hz, CH2),
1.18 (1H, dd, J ¼ 14.6, 7.7 Hz, CH2), 3.47–3.53 (1H, m, CH).
Under the same condition, the product analysis for
the solvolysis of 2-[3,5-bis(trifluoromethyl)phenyldimethylsilyl]-
1-methylethyl trifluoroacetate in CD3CD2OD was carried
—
[20] M. Fujio, N. Goto, T. Dairokuno, M. Goto, Y. Saeki, Y. Okusako, Y. Tsuno,
Bull. Chem. Soc. Jpn 1992. 65, 3072–3079.
[21] M. Goto, K. Funatsu, N. Arita, M. Mishima, M. Fujio, Y. Tsuno, Mem. Fac.
Sci., Kyushu Univ., Ser. C, 1989, 17(1), 123–138.
[22] C. J. Lancelot, D. J. Cram, P. v. R. Schleyer, in Carbonium ions Vol. 3,
Chapter 27 (Eds: G. A. Olah P. v. R. Schleyer), John Wiley & Sons, Inc.,
NY, 1972, pp. 1347–1483 and references therein.
[23] J. Vencl, J. Hetflejs, P. Kucera, J. Cermak, V. Chvalovsky, Collect. Czech.
Chem. Commun. 1973, 38, 1248–1255.
out at 75 8C, providing the formation of CH2 CHCH ,
—
3
3,5-(CF3)2C6H3Si(CH3)2CH2CH(CH3)OCD2CD3,
and
3,5-
1
(CF3)2C6H3Si(CH3)2CH2CH(CH3)OD (1:0.6:0.3). Propylene: H NMR
d 1.68 (3H, d, J ¼ 6.3 Hz, CH3), 4.88 (1H, d, J ¼ 10.0 Hz), 4.98 (1H, d,
J ¼ 16.9 Hz), 5.73–5.82 (1H, m). {Dimethyl[3,5-bis(trifluoromethyl)-
1
phenyl]}(2-ethoxypropyl)silane: H NMR d 1.15 (3H, d, J ¼ 5.8 Hz,
CH3), 3.50–3.54 (1H, m, CH). 1-{Dimethyl[3,5-bis(trifluoromethyl)-
1
phenyl]silyl}-2-propanol: H NMR d 1.19 (3H, d, J ¼ 6.3 Hz, CH3),
[24] J. Vencl, J. Hetflejs, J. Cermak, V. Chvalovsky, Collect. Czech. Chem.
Commun. 1973, 38, 1256–1262.
3.91–3.98 (1H, m, CH).
J. Phys. Org. Chem. 2010, 23 819–827
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