In summary, the bowl-to-bowl inversion of sumanene deriva-
tives were experimentally investigated using 2D-EXSY NMR,
which showed much slower inversion compared to that
of corannulene. DG{ of the deuteriosumanene 3 was 19.7–
20.4 kcal mol21, depending on the solvent. In bowl-to-bowl
inversion of PAHs, solvent effect was first addressed. The mono-
and di-anions of 3 showed a relatively rigid structure in solution.
Hexasubstituted derivatives 6 and 7 were successfully synthesized,
where a low inversion barrier was observed. Further structure–
dynamics relationships are now under investigation.
H. S. expresses his special thanks to the Center of Excellence
(21COE) program ‘‘Creation of Integrated EcoChemistry’’ of
Osaka University. This work was financially supported in part by
a Grant-in-Aid for Young Scientists (B) from Japan Society for the
Promotion of Science and collaborative development of innovative
seeds, potentiality verification stage from Japan Science and
Technology Agency (JST). Financial support from the Mitsubishi
Foundation is also acknowledged.
Notes and references
§ The NMR experiments for the measurement of the bowl-to-bowl
inversion were conducted with 20 mM of sumanene derivatives. First, the
longitudinal relaxation time T1 at the corresponding protons was measured
for each spectrum using the inversion–recovery method with the 180–t–90u
pulse sequence. 1D NOE experiments were carried out at various values of
mixing time tm. The optimum tm was evaluated to be that at which the
value of [integration for chemical exchange at 1D NOE experiment] 6
[S/N ratio] reaches a maximum. Relaxation decay d1 was determined from
eqn (1) where tac = acquisition time. Values of T1 and tm are summarized in
Table S1, ESI.{1
Fig. 3 Selected 1H NMR spectra of equilibration for (a) monoanion 4 at
283 K and (b) dianion 5 at 273 K (600 MHz, 22 mM, THF-d8). (*) Exo-
protons; (x) residual THF.
respectively) was observed at longer times in both spectra (Fig. 3(a)
and (b)). The half-life times were 2985 s for 4 at 283 K and 7547 s
for 5 at 273 K. The rate constants (k) for the reversible
equilibration of 4 and 5 were 9.10 6 1025 s21 at 283 K and
3.40 6 1025 s21 at 273 K, respectively (Table 1, entries 9 and 10),
determined by regression analysis using the equation 2kt = ln[a/
(a 2 2x)] where a is the initial concentration of 4a (or 5a) and x is
the concentration of 4b (or 5b) at time t. Correlation coefficients of
the linear regressions were 0.999 and 0.978 (for 4 and 5,
respectively, see Fig. S1 and S2, ESI{). DG{ values were 21.8
and 21.5 kcal mol21 for 4 and 5, respectively (Table 1, entries 9
and 10), calculated from the Eyring equation. Monoanion 4 and
dianion 5 show a 1.5 and 1.2 kcal mol21 higher barrier than that of
1, respectively.
3T1 = tac + tm + d1
2D EXSY (2D NOESY) experiments were performed with a spectrum
width of 8 ppm, with acquisition time of 0.213 s, using 1024 data points in
the t2 dimension and 512 in t1, with subsequent weighting with the sinebell
function with 16 scans for each t1 increment. Exchange cross-peaks were
integrated, which were then processed using EXSYCalc10 to give the
chemical exchange rate constant (k). The rate constant k was further
substituted to the Eyring equation to derive the activation energy (DG{).
1 J. C. Hanson and C. E. Nordman, Acta Crystallogr., Sect. B: Struct.
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2 L. T. Scott, M. M. Hashemi and M. S. Bratcher, J. Am. Chem. Soc.,
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Further studies were carried out with hexasubstituted suma-
nenes. The hexaallylated and hexa-p-methoxybenzylated suma-
nenes 6 and 7 were obtained by nucleophilic substitution reaction
of 1 with aqueous 30% NaOH solution as a base in the presence of
tetrabutylammonium bromide and a minimum amount of THF in
quantitative and 75% yields, respectively (Scheme 1(c)). Full
characterization for all protons and carbons was carried out by 1H
NMR, 13C NMR, 2D-NOESY, HMBC and HMQC experiments
(all spectra were shown in ESI{). The chemical exchange of Ha–
Ha9 and Hb–Hb9 was analyzed for 6 and 7, respectively. The
inversion barriers of 6 and 7 were 19.2 and 18.2 kcal mol21
(Table 1, entries 11 and 12), which are 1.2 and 2.2 kcal mol21
lower than that of 3, respectively. In terms of the inversion rate,
these values are approximately 7 and 35 times as fast as that of 3,
respectively. The facile inversion of hexasubstituted sumanenes
may be due to the steric repulsion of the bulky endo-substituents.
3 (a) A. Sygula, A. H. Abdourazak and P. W. Rabideau, J. Am. Chem.
Soc., 1996, 118, 339–343; (b) Z. Marcinow, A. Sygula, A. Ellern and
P. W. Rabideau, Org. Lett., 2001, 3, 3527–3529.
4 T. J. Seiders, K. K. Baldridge, G. H. Grube and J. S. Siegel, J. Am.
Chem. Soc., 2001, 123, 517–525.
5 H. Sakurai, T. Daiko and T. Hirao, Science, 2003, 301, 1878.
6 H. Sakurai, T. Daiko, H. Sakane, T. Amaya and T. Hirao, J. Am.
Chem. Soc., 2005, 127, 11580–11581.
7 T. Amaya, K. Mori, H.-L. Wu, S. Ishida, J. Nakamura, K. Murata and
T. Hirao, Chem. Commun., 2007, 1902–1904.
8 U. D. Priyakumar and G. N. Sastry, J. Phys. Chem. A, 2001, 105,
4488–4494.
9 C. L. Perrin and T. J. Dwyer, Chem. Rev., 1990, 90, 935–967.
10 Calculated using EXSYCalc (distributed by Mestrelab research: http://
www.mestrec.com/).
32
11 In contrast, the bowl-to-bowl inversion of benzylic trianion C21H9
was calculated to give a lower energy barrier than that of 1, see:
U. D. Priyakumar and G. N. Sastry, J. Mol. Struct. (THEOCHEM),
2004, 674, 69–75.
This journal is ß The Royal Society of Chemistry 2008
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