Acknowledgements
This work was supported by Grants-in-Aid for COE Research
Design and Control of Advanced Molecular Assembly Sys-
‘
tems’ (#08CE2005) and for Scientific Research (B) (#06453035)
from the Ministry of Education, Science, Sports and Culture,
Japan.
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Fig. 6 Field dependence of magnetization of 1 measured at 2.0 K.
Two solid curves are a theoretical S = 1 curve (top) and a best-fit curve
(
bottom) with a singlet–triplet gap of 2J/k = Ϫ0.76 K [eqn. (4)].
B
2
3
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1
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Experimental
H and C NMR spectra were recorded on a JEOL EX-270
instrument. UV–VIS spectra were obtained on a Hitachi U-
300 spectrophotometer. 2-Methyltetrahydrofuran (MTHF)
1
13
3
used in the magnetic measurements was purified by succes-
sive distillation from lithium aluminium hydride and from
sodium–benzophenone ketyl under a dry nitrogen atmos-
phere.
5
726.
Preparation of 5,6-dimethylene-2,3-diazabicyclo[2.2.2]oct-2-ene
4
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(
2)
Compound 2 was obtained from 1,2-dihydrophthalic acid
1
0
according to the method of Roth et al1. and obtained as pale
0
yellow crystals: mp 37.5–39.5 ЊC (lit., 40 ЊC); δ (270 MHz;
H
CDCl ) 1.4–1.7 (AB system, 4 H), 5.03 (s, 2 H), 5.34 (s, 2 H),
3
2
6, 1285; ( f ) P. Dowd, W. Chang and Y. H. Paik, J. Am. Chem. Soc.,
5
.66 (s, 2 H); δ (67.8 MHz; CDCl ) 21.8, 71.5, 107.1, 137.7;
C 3
Ϫ1 Ϫ1
1987, 109, 5284; (g) W. R. Roth, R. Langer, M. Bartmann,
B. Stevermann, G. Maier, H. P. Reisenauer, R. Sustmann and
W. Müller, Angew. Chem., Int. Ed. Engl., 1987, 26, 256.
λmax(CH Cl )/nm (ε/
cm ) 274 (4990), 379 (112) nm
ϩ
2
2
ϩ
[
[
Found: MH , 135.0920. Calc. for C H N (MH ): 135.0922]
8 11 2
10
lit., Found: M Ϫ N , 106.0771. Calc. for C H (M Ϫ N ):
5 (a) T. Matsumoto, N. Koga and H. Iwamura, J. Am. Chem. Soc.,
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2
8
10
2
1
06.0782].
EPR measurements
Photolysis of the azoalkane precursor was carried out in
MTHF matrices at 9 K in the EPR cavity. Light was obtained
from a high-pressure mercury lamp with a Kenko sharp-cut
filter. A Bruker ESP 300 spectrometer was used to obtain
X-band EPR spectra. Temperatures were controlled by an Air
Products LTD-3-110 cryogenic temperature controller. The
cryostat was maintained at high vacuum by a diffusion/rotary
pump set.
6
(a) L. C. Bush, R. B. Heath and J. A. Berson, J. Am. Chem. Soc.,
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J. C. Scaiano and J. A. Berson, J. Am. Chem. Soc., 1997, 119, 1406;
(
c) L. C. Bush, L. Maksimovic, X. W. Feng, H. S. M. Lu and J. A.
Berson, J. Am. Chem. Soc., 1997, 119, 1416.
H. Iwamura and N. Koga, Acc. Chem. Res., 1993, 26, 346.
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214, 451.
7
8
Magnetic measurements. Magnetic measurements were per-
formed on a Quantum Design MPMS-5S SQUID susceptom-
eter. Blank data due to sample holder, a quartz cell, and light
guide were subtracted from the data after irradiation. This
technique is found to be very sensitive because the blank data
originate from the same sample. A solution of 0.33 mg of 2 in
9 Another paper in this issue reports the results of a study of the
singlet–triplet splitting in the parent TME diradical by
photoelectron spectroscopy, E. P. Clifford, P. G. Wenthold, W. C.
Lineberger, G. B. Ellison, C. X. Wang, J. J. Grabowski, F. Vila and
K. D. Jordan, J. Chem. Soc., Perkin Trans. 2, 1998, 1015.
0 W. R. Roth, M. Biermann, G. Erker and K. Jelich, Chem. Ber., 1980,
113, 586.
11 (a) M. Rule, A. R. Matlin, D. E. Seeger, E. F. Hilinski, D. A.
Dougherty and J. A. Berson, Tetrahedron, 1982, 38, 787; (b) B. L. V.
Prasad and T. P. Radhakrishnan, J. Mol. Struct. (THEOCHEM),
1
1
0 ml of MTHF was placed in a quartz cell. Light (λ > 320 nm),
obtained from a Xenon lamp in combination with a Kenko
sharp-cut filter and an OCLI B cold mirror, was introduced into
the SQUID susceptometer through an optical fiber inserted
into the sample probe and the photolysis of 2 in MTHF was
performed at 4–10 K for 14 h. The paramagnetic susceptibility
χ was obtained at a field of 5000 G in the temperature range
1
996, 361, 175; (c) Z. Havlas and J. Michl, J. Mol. Struct.
(
THEOCHEM), 1997, 398–399, 281.
Paper 7/06301F
2
–20 K. The field-dependence of magnetization (M) of 1 was
Received 28th August 1997
obtained at 2.0 K.
Accepted 2nd December 1997
1
026
J. Chem. Soc., Perkin Trans. 2, 1998