A. Happer et al. / Journal of Organometallic Chemistry 659 (2002) 10ꢀ
/14
13
stronger hyperconjugation in 8 are also apparent in the
magnitudes of the 13Cꢀ13
C one bond coupling constants
within the pyridine ring, thus methylation of 9 results in
a decrease in the Ci ÃCo from 54.3 to 52.9 Hz and an
increase in the Co ÃCm from 58.7 to 61.1 Hz reflecting
the greater contribution of the resonance form 8? to the
ground state structure of 8. The CH2ꢀCi coupling
NMR d 8.6 (2H), 7.18 (2H), 4.05 (3H), 2.15 (3H), ꢃ
/
0.21
(9H) 13C-NMR: d 161.7, 142.4, 124.8, 46.5, 29.1, ꢃ
3.3.
/
/
/
3.4. Preparation of N-methyl 4-trimethylsilylpyridinium
triflate (8×triflate)
/
/
/
A solution of 9 (100 mg) in deutero acetonitrile (0.5
ml) was treated with neat methyl triflate (1.05 equiva-
lents). The resulting solution was left at 08 overnight
constant is not sensitive to the effects of hyperconjuga-
tion, this has been observed previously [30].
whereupon large colourless blocks of (8×
/
triflate) m.p.
192ꢀ193 (d) suitable for X-ray analysis had formed.
/
2. Conclusion
3.5. Preparation of N-methyl 4-picolinium tosylate
Solid state and solution evidence for the presence of
strong hyperconjugation (sꢀp conjugation) between the
/
A solution of 4-picoline (0.5 g, 0.0054 mol)) in
diethylether (20 ml) was treated with a solution of
methyltosylate (1.1 g, 0.0059 mmol) in diethylether 95
ml). After leaving for 24 h the resulting precipitate was
CH2ÃSi s bonding orbital and the charged pyridinium p
/
system has been demonstrated.
filtered. Recrystallisation from methanolꢀ
/
diethylether
3. Experimental
gave 12×tosylate as thick plates, m.p. 152ꢀ1538.
/
/
3.1. X-ray structure determinations
4. Supplementary material
Data were collected on an Enraf Nonius CAD-
4Machs single crystal diffractometer in the v ꢀ2u scan
mode K. The temperature was maintained at 130.0(2)
during the data collections using an Oxford Cryostream
cooling device. Solution by direct methods (SHELXS-86)
[31] and refinement using SHELXL-97 [32]. Thermal
/
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 184367 and 184368 for
compounds 8×
/
triflate and 12×/tosylate. Copies of this
information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
ellipsoid plots were generated by the program ORTEP
[33], within the WINGX [34] suite of programs.
3
1EZ, UK (Fax: ꢂ44-1223-336033; e-mail: deposit@
/
General experimental details have been published in a
previous paper [26].
3.2. Preparation of 4-trimethylsilylmethylpyridine (9)
Acknowledgements
A solution of 4-picoline (5.3 g, 0.056 mol) in ether (50
ml) was treated with a solution of methyllithium (1.4 M
1.05 equivalents) and heated to reflux for 30 min. Upon
cooling the resulting slurry was carefully pippetted into
a solution of chlorotrimethylsilane (1.5 equivalents) in
ether (50 ml). The resulting mixture was stirred for 30
min then quenched by the addition of water. The ether
Our thanks go to the Australian Research Council
and the Petroleum Research Fund for supporting this
work.
References
layer was separated, washed with water (2ꢄ
/
50 ml) dried
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(MgSO4) and evaporated down to a pale yellow oil (8.1
1
g) 86% H-NMR: d (CDCl3) 8.21 (2H, d, Jꢁ
6.73, (2H, d, Jꢁ5.5 Hz), 1.9 (2H, s), ꢃ
0.17 (9H, s). 13C-
NMR: d (CDCl3) 149.8 (Ci), 148.8, 123.1, 26.9, ꢃ2.45.
/
5.5 Hz),
/
/
[4] M.C.R. Symons, Tetrahedron 18 (1961) 333.
[5] A.R. Bassindale, C. Eaborn, D.R.M. Walton, D.J. Young, J.
Organomet. Chem. 20 (1969) 49.
/
3.3. Preparation of methyl 4-trimethylsilylpyridinium
iodide (8×iodide)
[6] W. Adcock, D.P. Cox, W. Kitching, J. Organomet. Chem. 133
(1977) 393.
/
[7] W. Adcock, B.F. Hegarty, W. Kitching, A.J. Smith, J. Organo-
met. Chem. 12 (1968) 21.
A solution of 9 (100 mg) in deuterochloroform (0.5
ml) was treated with methyl iodide (1.1 equivalents),
after 24 h the 1H- and 13C-NMR signals characteristic of
9 had disappeared and were replaced by those of 8.1H-
[8] A.J. Smith, W. Adcock, W. Kitching, J. Am. Chem. Soc. 92
(1970) 6140.
[9] W. Adcock, S.Q.A. Rizvi, W. Kitching, J. Am. Chem. Soc. 94
(1972) 3657.