Preparation of Oligodiazo Compounds by Using the Suzuki Coupling Reaction and Characterization of Their Photoproducts

Article abstract of DOI:10.1021/ja038450p

[9-{10-(4-tert-Butyl-2,6-dimethyl)phenyl}anthryl](4-bromo-2, 6-dimethylphenyl)diazomethane was found to be stable enough to survive under Suzuki coupling conditions and underwent mono-, di-, and trisubstitution with benzene mono-, di-, and triboronic acid

Full text of DOI:10.1021/ja038450p

Published on Web 01/10/2004
Preparation of Oligodiazo Compounds by Using the Suzuki
Coupling Reaction and Characterization of Their
Photoproducts
Tetsuji Itoh,† Katsuyuki Hirai,‡ and Hideo Tomioka*,†
Contribution from the Chemistry Department for Materials, Faculty of Engineering, and
Instrumental Analysis Facilities, Life Science Research Center, Mie UniVersity,
Tsu, Mie 514-8507 Japan
Received September 10, 2003; E-mail: tomioka@chem.mie-u.ac.jp
Abstract: [9-{10-(4-tert-Butyl-2,6-dimethyl)phenyl}anthryl](4-bromo-2,6-dimethylphenyl)diazomethane was
found to be stable enough to survive under Suzuki coupling conditions and underwent mono-, di-, and
trisubstitution with benzene mono-, di-, and triboronic acids to afford benzene derivatives having one, two,
and three diazo units, respectively. The products from irradiation of those diazo compounds were
characterized by ESR and SQUID measurements, which revealed that triplet, quintet, and septet ground
states were formed from mono-, bis-, and tris(diazo) compounds, respectively. The stability of those high-
spin species was estimated by temperature-dependent ESR and UV/vis measurements as well as laser
flash photolysis, which indicated that all three species are stable up to 160 K and have a half-life of a few
seconds in solution at room temperature. The finding unequivocally shows that a precursor diazo unit can
basically be handled as a building block to construct ploydiazo compounds and that persistent triplet
carbenes, even though they greatly lose typical reactivity as a triplet carbene, still retain electronic properties
and act as a spin source when aligned properly in the π-electron frameworks to generate a high-spin
molecule with remarkable thermal stability.
There has been an ever-increasing interest in molecular
magnetism, in which spins of unpaired electrons in p-orbitals
of light atoms such as carbon, nitrogen, and oxygen are mainly
responsible; in addition, many attempts have been made to
realize organic ferromagnetic materials.1,2 Spin sources used for
such studies are mostly thermodynamically stable radicals, such
as galvinoxyls,2j triphenylmethyls,3a and nitroxides,3b mostly
because of their ease of preparation and operation. Potential
problems emerge for these radicals. For instance, the exchange
coupling between the neighboring nitroxides is weak, and, hence,
contamination of the lower-spin states in the polyradicals cannot
be avoided. Triplet carbenes are regarded as one of the most
effective spin sources because the magnitude of the exchange
coupling between the neighboring centers is large.4,5 Moreover,
the photolytic production of polycarbenes is possible in solid
solution at cryogenic temperatures if poly(diazo) precursors are
available. Actually, Iwamura and co-workers have prepared a
“starburst-”type nonadiazo compound and have demonstrated
that nine diazo groups are photolyzed at low temperature to
give a nonadecet ground state (S ) 9).5
However, those systems have two disadvantages that hinder
their further extension to usable magnetic materials. First, a
triplet carbene unit is highly unstable and lacks the stability for
practical application under ambient conditions. To overcome
these difficulties, we have made great efforts to stabilize and
hopefully isolate the triplet carbene and succeeded in preparing
fairly stable ones surviving for minutes in solution and for years
in the crystalline state at room temperature.6 Therefore, the next
step is to explore a way to connect them while retaining a robust
π-spin polarization.
† Chemistry Department for Materials.
‡ Instrumental Analysis Facilities.
(1) (a) Iwamura, H. AdV. Phys. Org. Chem. 1990, 26, 179. (b) Dougherty, D.
A. Acc. Chem. Res. 1991, 24, 88. (c) Rajca, A. Chem. ReV. 1994, 94, 871.
(2) (a) Kahn, O. Molecular Magnetism; VCH Publishers: Weinheim, 1993.
(b) Gatteschi, D. AdV. Mater. 1994, 6, 635. (c) Miller, J. S.; Epstein, A. J.
Angew. Chem., Int. Ed. Engl. 1994, 33, 385. (d) Miller, J. S.; Epstein, A.
J. Chem. Eng. News 1995, October 2, 30. (e) Kahn, O., Ed. Magnetism:
A Supramolecular Function; NATO ASI Series C; Kluwer: Dordrecht,
1996. (f) Turnbull, M. M., Sugimoto, T., Thompson, L. K., Eds. Molecule-
Based Magnetic Materials; ACS Symposium Series 644; ACS: Washing-
ton, 1996. (g) Gatteschi, D. Curr. Opin. Solid State Mater. Sci. 1996, 1,
192. (h) Miller, J. S., Epstein, A. J., Eds. MRS Bull. 2000, 25, 21. (i) Miller,
J. S., Drillon, M., Eds. Magnetism: Molecules to Materials II; Wiley-
VCH: New York, 2001. (j) Molecular Magnetism; Itoh, K., Kinoshita,
M., Eds.; Kodansha-Gordon and Breach: Tokyo, 2000.
(4) (a) Koga, N.; Iwamura, H. In Carbene Chemistry; Bertrand, G., Ed.; Fontis
Media: Lausanne, 2002; pp 271-296. (b) Matsuda, K.; Nakamura, N.;
Takahashi, K.; Inoue, K.; Koga, N.; Iwamura, H. Molecule-based Magnetic
Materials; ACS Symposium Series 644; ACS: Washington, 1996; p 142.
(5) (a) Nakamura, N.; Inoue, K.; Iwamura, H.; Fujioka, T.; Sawaki, Y. J. Am.
Chem. Soc. 1992, 114, 1484. (b) Nakamura, N.; Inoue, K.; Iwamura, H.
Angew. Chem., Int. Ed. Engl. 1993, 32, 872. (c) Matsuda, K.; Nakamura,
N.; Takahashi, K.; Inoue, K.; Koga, N.; Iwamura, H. J. Am Chem. Soc.
1995, 117, 5550. (d) Matsuda, K.; Nakamura, N.; Inoue, K.; Koga, N.;
Iwamura, H. Chem.-Eur. J. 1996, 2, 259. (e) Matsuda, K.; Nakamura, N.;
Inoue, K.; Koga, N.; Iwamura, H. Bull. Chem. Soc. Jpn. 1996, 69, 1483.
(6) (a) Tomioka, H. Acc. Chem. Res. 1997, 30, 315. (b) Tomioka, H. In
AdVances in Carbene Chemistry; Brinker, U., Ed.; JAI Press: Greenwich,
CT, 1998; Vol. 2, pp 175-214. (c) Tomioka, H. In Carbene Chemistry;
Bertrand, G., Ed.; Fontis Media S. A.: Lansanne, 2002; pp 103-152.
(3) (a) Bushby, R.-J. In Magnetism: Molecules to Materials II; Miller, J. S.,
Drillon, M., Eds.; Wiley-VCH: Weinheim, 2001; pp 149-187. (b)
Amabilino, D. B.; Viciana, J. In Magnetism: Molecules to Materials II;
Miller, J. S., Drillon, M., Eds.; Wiley-VCH: Weinheim, 2001; pp 1-60.
9
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J. AM. CHEM. SOC. 2004, 126, 1130-1140
10.1021/ja038450p CCC: $27.50 © 2004 American Chemical Society

Preparation of Oligodiazo Compounds
A R T I C L E S
Scheme 1
The second disadvantage that arises is that diazo groups are
also generally labile7 and, hence, are usually introduced at the
last step of synthesis.5 In other words, the diazo compound
cannot be used as a building block to prepare a more
complicated polydiazo compound, and, thus, the synthesis of
the precursor diazo compounds becomes more difficult and
laborious as the number of diazo units increases. We found,
almost accidentally, that a diphenyldiazomethane prepared to
generate a persistent triplet carbene is also persistent for the
diazo compound and, hence, can be further modified, with the
diazo group intact, into a more complicated diazo compound.
For instance, bis(2,4,6-tribromophenyl)diazomethane is found
to be stable enough to survive under Sonogashira coupling
reaction conditions and undergoes a coupling reaction with
(trimethylsilyl)acetylene to give bis(2,6-dibromo-4-trimethyl-
silylethynylphenyl)diazomethane. Three units of the diazo com-
pound are introduced at the 1-, 3-, and 5-positions of the benzene
ring through the ethynyl group by employing a similar coupling
reaction to give a tris(diazo) compound, which eventually
generates a fairly stable septet ground-state tris(carbene) upon
irradiation.8
is a report of the preparation of an oligo(diazo) compound using
the Suzuki coupling reaction and the characterization of oligo-
(carbene) generated from those precursor oligo(diazo) com-
pounds.
Results and Discussion
Synthesis of Precursor Oligodiazo Compounds. The diazo
unit we used in this study was the one having 10-(4-tert-butyl-
2,6-dimethylphenyl)anthryl and 4-bromo-2,6-dimethylphenyl
groups, which can generate a fairly persistent triplet carbene.10
To test the stability of the diazomethane under Suzuki coupling
conditions, we first treated it with phenylboronic acid in the
presence of Pd(OAc)2 as a catalyst with P(tBu)2(2-BP) as a
ligand and KF as a base in tetrahydrofuran (THF) at 40 °C
(Scheme 1). The usual workup gave the desired phenylated
compound (1-N2) as an orange solid in 88% yield with the diazo
group intact. Encouraged by the finding, we reacted the
diazomethane with 5-trimethysilylbenzene-1,3-diboronic acid
under similar conditions. The 1,3-bis(diazo) compound (2-2N2)
was obtained as an orange solid in 51% yield in this case.
Coupling with benzene-1,3,5-triboronic acid did not work under
similar conditions. However, trisubstitution was realized by
using tetrabutylammonium bromide and K3PO4, in place of the
phosphine and base, respectively, in dimethylformamide (DMF)
at 40 °C (Scheme 2).11
These results suggest that the diazo compound can be used
as a building block to prepare a polydiazo compound, which
can then generate high-spin polycarbene with considerable
thermal stability. Thus, it is very important to explore the
applicability of this approach, as it may open a window to a
new route to organic magnetic materials. We found that
diaryldiazomethane is stable enough to survive the Suzuki
coupling reaction.9 This enables us to introduce the diazo unit
to a phenyl ring directly without using the ethynyl group. This
All of the diazo compounds were purified by TLC followed
by a repeated chromatograph on a gel permeation column.
Appreciable decomposition of the diazo group was not noted
in all cases, at least under the conditions employed here. The
diazo compounds were fairly stable and could be stored in a
refrigerator for several months without any appreciable decom-
position.
(7) Regitz, M.; Maas, G. Diazo Compounds-Properties and Synthesis; Aca-
demic Press: Orlando, 1986.
(8) Tomioka, H.; Hattori, M.; Hirai, K.; Sato, K.; Shiomi, D.; Takui, T.; Itoh,
K. J. Am. Chem. Soc. 1998, 120, 1106.
(9) For reviews, see for example: (a) Suzuki, A. In Metal-Catalyzed Cross-
Coupling Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-VCH:
Weinheim, 1998; pp 49-97. (b) Stanforth, S. P. Tetrahedron 1998, 54,
263.
(10) (a) Tomioka, H.; Nakijima, J.; Mizuno, H.; Iiba, E.; Hirai, K. Can. J. Chem.
1999, 77, 1066. (b) Itakura, H.; Tomioka, H. Org. Lett. 2000, 2, 2995. (c)
Takahashi, Y.; Tomura, M.; Yoshida, K.; Murata, S.; Tomioka, H. Angew.
Chem., Int. Ed. 2000, 39, 3478. (d) Tomioka, H.; Iwamoto, E.; Itakura,
H.; Hirai, K. Nature 2001, 412, 626.
(11) Zim, D.; Monteiro, L.; Dupont, J. Tetrahedron Lett. 2000, 41, 8199.
9
J. AM. CHEM. SOC. VOL. 126, NO. 4, 2004 1131

A R T I C L E S
Itoh et al.
Scheme 2
Spectroscopic Studies
ESR Studies. Irradiation (λ > 350 nm) of 1-N2 in 2-methyl-
tetrahydrofuran (2-MTHF) at 77 K gave rise to a paramagnetic
species (Figure 1a) readily characterized from its ESR spectrum
as a derivative of a triplet carbene (31).12 The ESR signals were
persistent at this low temperature but disappeared irreversibly
when the matrix temperature was raised to room temperature
and recooled to 77 K. The EPR signals were analyzed in terms
of the zero-field splitting (ZFS) parameters, which gave D )
0.1950 cm-1 and E ) 0.0033 cm-1
.
To estimate the temperature at which the triplet signals
disappear, the 2-MTHF glass containing carbene 31 was warmed
gradually in 10 K increments to a desired temperature, allowed
to stand at that temperature for 5 min, and recooled to 77 K to
measure the ESR. When the 2-MTHF glass was warmed to
around 100 K, a new set of triplet peaks (D ) 0.1532 cm-1
and E ) 0.0008 cm-1) appeared at the expense of the original
peaks (Figure 1b). These changes were not reversible; when
the sample was cooled to 77 K, no change took place, except
that the signal intensity increased according to the Curie law.
Changes of this kind have often been observed for sterically
congested triplet diarylcarbenes and are usually interpreted in
terms of geometrical changes.12c,13 The new set of signals started
to decrease at around 140 K and disappeared completely at 160
K.
Similar irradiation of the bis(diazo) compound (2-2N2) in
2-MTHF at 77 K gave ESR spectra (Figure 2a) that were
(12) See for reviews of the EPR spectra of triplet carbenes: (a) Sander, W.;
Bucher, G.; Wierlacher, S. Chem. ReV. 1993, 93, 1583. (b) Trozzolo, A.
M.; Wasserman, E. In Carbenes; Jones, M., Jr., Moss, R. A., Eds.; Wiley:
New York, 1975; Vol. 2, pp 185-206. (c) Tomioka, H. In AdVances in
Strained and Interesting Organic Molecules; Halton, B., Ed.; JAI Press:
Greenwich, CT, 2000; Vol. 8, pp 83-112.
(13) When a carbene is generated in rigid matrices at very low temperature, it
should have the geometry dictated by that of the precursor. Even if the
thermodynamically most stable geometry of the carbene is different from
that at birth, the rigidity of the matrices prevents the carbene from achieving
its minimum-energy geometry. When matrices are softened by annealing,
the carbene undergoes relaxation to the preferred geometry, probably to
gain relief from steric compression.
Figure 1. (a) ESR spectra obtained by irradiation of monodiazo compound
1-N2 in 2-methyltetrahydrofuran at 77 K. (b-e) ESR spectra observed at
77 K in 2-methyltetrahydrofuran after warming the matrix containing 31 to
(b) 100, (c) 120, (d) 140, (e) 160, and (f) 180 K.
completely different from those observed for the corresponding
monocarbene 32. The spectra showed rather strong signals
centered at around 300 mT along with weak signals ascribable
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1132 J. AM. CHEM. SOC. VOL. 126, NO. 4, 2004

Preparation of Oligodiazo Compounds
A R T I C L E S
Figure 2. (a) ESR spectra obtained by irradiation of bis(diazo) compound
2-2N2 in 2-methyltetrahydrofuran at 77 K. (b) Simulated spectra of 52 with
S ) 2, g ) 2.003, D ) 0.027 cm-1, and E ) 0.008 cm-1. (c-g) ESR
spectra observed at 77 K in 2-methyltetrahydrofuran after warming the
Figure 3. (a) ESR spectra obtained by irradiation of tris(diazo) compound
3-3N2 in 2-methyltetrahydrofuran at 77 K. (b) Simulated spectra of 73 with
S ) 3, g ) 2.003, D ) 0.0015 cm-1, and E ) 0.001 cm-1. (c-g) ESR
spectra observed at 77 K in 2-methyltetrahydrofuran after warming the
5
matrix containing 2 to (c) 120, (d) 140, (e) 160, (f) 180, and (g) 200 K.
7
matrix containing 3 to (c) 120, (d) 140, (e) 160, (f) 180 and, (g) 200 K.
to a triplet species. The latter signals are assigned to triplet
monocarbene (32) probably formed as a result of incomplete
decomposition of the bis(diazo) compound. The major signals
are well reproduced by computer simulation,14 shown in Figure
2b, employing a quintet Hamiltonian with S ) 2, g ) 2.003, D
) 0.027 cm-1, and E ) 0.008 cm-1. We, therefore, assign the
spacing observed here, in comparison to that for the quintet
biscarbene, is consistent with the tendency that as the spin
multiplicity became higher, the D values became smaller. As
shown by the simulation14 shown in Figure 3b, these peaks can
be fitted to a septet tris(carbene) spectrum with parameters S
) 3, g ) 2.003, D ) 0.015 cm-1, and E ) 0.001 cm-1. Thus,
5
signals to quintet biscarbene 2, 2. The quintet signals do not
decay appreciably up to 140 K, start to decompose at around
150 K, and disappear irreversibly above 160 K.
7
we assign the signals to septet tri(carbene) 3, 3. The signals
are also stable up to 140 K, but they decay irreversibly above
160 K.
Irradiation of the tris(diazo) compound (3-3N2) again gave
ESR spectra (Figure 3a) that were completely different from
those observed for either monocarbene or biscarbene. The main
spectra consisted of well-resolved signals centered around ca.
335 mT; signals attributable to triplet carbene and quintet bis-
(carbene) were very weak, if at all detected. The smaller signal
It is interesting to note that high-spin species are likely formed
as a main product at the initial stage of irradiation without the
intervention of a lower-spin state. A similar observation has
been reported in the photolysis of “simple” poly(diphenyldiazo-
mathane) in a matrix at low temperature and is explained by
assuming that the excess energy after removal of a nitrogen
molecule in the photoexcited state can be transferred intramo-
lecularly to other diazo groups in a matrix where the dissipation
(14) (a) Teki, Y. Thesis, Osaka City University, Osaka, Japan, 1985. (b) Teki,
Y.; Takui, K.; Yagi, H.; Itoh, K.; Iwamura, H. J. Chem. Phys. 1985, 83,
539. (c) Takui, K. In Molecular Magnetism in Organic-Based Materials;
Lahti, P. M., Ed.; Marcel Dekker: New York, 1999.
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A R T I C L E S
Itoh et al.
Figure 4. (a) Plot of magnetization (M in emu) as a function of irradiation time observed in the photolysis of bis(diazo) compound 2-2N2 in 0.10 mM
2-methyltetrahydrofuran matrix measured at 5.0 K and 5 kOe. (b) Field dependence of the magnetization of the photoproduct from bis(diazo) compound
2-2N2 in 0.10 mM 2-methyltetrahydrofuran matrix measured at 2.0 and 5.0 K. Mb and Ma refer to the magnetization value before and after irradiation,
respectively, and M ) Ma - Mb.
of excess energy is inefficient.15a However, it is to be noted
here that photodeazetation processes are sensitive to experi-
mental conditions such as wavelength and intensities of the light
and concentration of the precursor.15b-d One needs more
elaborated works to make the process clearer.
SQUID Measurements. To confirm whether the high-spin
states observed for mono- to tricarbenes are in the ground state
or not, magnetic measurements were carried out.
The 2-MTHF solution of bis(diazo) compounds (2-2N2) was
placed inside the sample compartment of a superconducting
quantum interference device (SQUID) magnet/susceptometer
and was irradiated at 5-10 K with a light (λ ) 488 nm) from
an argon ion laser through an optical fiber. The development
on magnetization (M/emu) at 5 K in a constant field of 5 kOe
with the irradiation time for the bis(diazo) compound was
Figure 5. Plot of M/Ms versus H/T of the photoproduct from mono- (1-
N2: X, +), bis- (2-2N2: b, 9), and tris(diazo) compound (3-3N2: O, 0)
measured at 2.0 (O) and 5.0 (0) K. The solid lines represent theoretical
measured in situ and is shown in Figure 4a. As the irradiation
time increased, the M values gradually increased and reached
a plateau after several hours. After the M values reached a
plateau, the magnetization values after irradiation, Ma, were
measured at 2.0 and 5.0 K in a field range of 0-50 kOe. The
magnetization values of the sample before irradiation, Mb,
were also measured under the same conditions. The magnetiza-
tion (M) due to the species generated by photolysis was then
obtained by subtracting the corresponding values obtained before
and after irradiation (Figure 4b). Thus, the effect of any
paramagnetic impurities could be canceled by this treatment.
The plots of the magnetization normalized by the saturation
magnetization (M/Ms) versus the temperature-normalized mag-
netic field (H/T) were analyzed in terms of the Brillouin function
as follows:1c,5,16
curves with S ) 1, 2, and 3.
angular momentum, µB is the Bohr magneton, g is the Lande´
g-factor, and kb is the Boltzmann constant. Because these
carbenes are constituted of light elements, the orbital angular
momentum should be negligible, and J can be replaced with
the spin quantum number S. The M/Ms versus H/T plots are
shown in Figure 5 together with theoretical curves with S ) 1,
2, and 3.17
The observed data for the bis(diazo) compound traced the
theoretical curve with S ) 2. The observed data were fitted
with eq 1 with S ) 1.92 and F ) 0.56. The value is close to
the theoretical value of 2, indicating that the two carbene centers
interact ferromagnetically to produce a quintet ground state, as
was expected. Because the magnetization data at two different
temperatures were fitted to the same Brillouin function, the
sample is considered to be free from ferro- or antiferromagnetic
intermolecular interactions, and the quintet state is considered
to be a ground state.
M ) Ma - Mb ) FNgJµBB(ø)
(1)
where F is the photolysis factor of diazo compound, N is the
number of the molecule, J is the quantum number for the total
(15) (a) Sugawara, T.; Inada, M.; Iwamura, H. Tetrahedron Lett. 1983, 24, 1723.
(b) Teki, Y.; Takui, T.; Yagi, H.; Katoh, K.; Iwamura, H. J. Chem. Phys.
1985, 83, 539. (c) Matsuda, K.; Nakamura, N.; Inoue, K.; Koga, N.;
Iwamura, H. Bull. Chem. Soc. Jpn. 1996, 69, 1483. (d) Nakamura, N.; Inoue,
K.; Iwamura, H. Angew. Chem., Int. Ed. Engl. 1993, 32, 872.
The data obtained for photoproducts from similar irradiation
of tris- and mono(diazo) compounds were also analyzed in a
(16) Carlin, R. L. Magnetochemistry; Springer-Verlag: Berlin, 1986.
(17) Ms values obtained from the best fitted curves were used.
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Preparation of Oligodiazo Compounds
A R T I C L E S
Figure 7. UV/vis spectra obtained by irradiation of bis(diazo) compound
2-2N2. (A) (a) Spectra of 2-2N2 in 2-methyltetrahydrofuran at 77 K. (b)
The same sample after irradiation (λ > 350 nm). (c) The same sample after
thawing to 100 K. (B) UV/vis spectral change measured at 10 K increments
upon thawing the same sample from 110 to 220 K.
Figure 6. UV/vis spectra obtained by irradiation of monodiazo compound
1-N2. (A) (a) Spectra of 1-N2 in 2-methyltetrahydrofuran at 77 K. (b) The
same sample after irradiation (λ > 350 nm). (c) The same sample after
thawing to 110 K. (B) UV/vis spectral change measured at 10 K increments
upon thawing the same sample from 110 to 200 K.
358, 414, and 438 nm (Figure 6). Because ESR signals
ascribable to triplet carbene are observed under identical
conditions, the absorption spectrum can be safely assigned to
similar manner to give S ) 2.56 and 0.96 and F ) 0.55 and
1.00, respectively. Again the values are close to the theoretical
values. Therefore, the result of the field dependence of M for
photoproducts from 2-2N2 and 3-3N2 suggests that a persistent
triplet diarylcarbene unit incorporated into a π-network in a
ferromagnetic fashion indeed acts as a spin source to generate
a high-spin ground state.
UV/Vis Spectroscopic Study in a Matrix at Low Temper-
ature. To examine the stability of those high-spin species in
solution at room temperature, it is necessary to know the UV/
vis spectroscopic feature of the species, because time-resolved
UV/vis spectroscopy is most conveniently employed for such
a study.6,18
3
triplet carbene 1. When the matrix was gradually thawed, the
bands become sharper, and the bands at longer wavelength, that
is, 414 and 438 nm, shifted a bit to 412 and 436 nm,
respectively, at around 100 K. This change can be attributed to
the geometrical change of the triplet carbene associated with a
change in viscosity of the matrixes upon annealing, as has been
revealed in ESR experiments. Upon further thawing, the band
started to disappear at around 130 K and completely vanished
at around 170 K.
Similar irradiation of bis- (2-2N2) and the tris(diazo) com-
pounds (3-3N2) in a 2-MTHF matrix at 77 K again resulted in
rapid disappearance of the original absorption due to diazo
compounds and concurrent growth of sharp and strong absorp-
tion bands at 354, 414, and 439 nm and 356, 413, and 442 nm,
respectively, which are very similar to those of the triplet
monocarbene 31 (Figures 7 and 8). Again, because ESR signals
ascribable to 52 and 73 are observed under identical conditions,
the absorption spectra can be assigned to quintet and septet
states. The similarity of the spectra with those of the monocar-
bene also supports the assignments; diradical centers introduced
Irradiation of 1-N2 in a 2-MTHF matrix at 77 K resulted in
rapid disappearance of the original absorption due to 1-N2 and
concurrent growth of sharp and strong absorption bands at 340,
(18) For reviews of the laser flash photolysis study of carbenes, see: (a) Moss,
R. S.; Turro, N. J. In Kinetics and Spectroscopy of Carbenes and Biradicals;
Platz, M. S., Ed.; Plenum Press: New York, 1990; pp 213-238. (b) Platz,
M. S.; Maloney, V. M. In Kinetics and Spectroscopy of Carbenes and
Biradicals; Platz, M. S., Ed.; Plenum Press: New York, 1990; pp 239-
352. (c) Moss, R. A. In AdVances in Carbene Chemistry; Brinker, U. H.,
Ed.; JAI Press: Greenwich, 1994; pp 59-88. (d) Jackson, J. E.; Platz, M.
S. In AdVances in Carbene Chemistry; Brinker, U. H., Ed.; JAI Press:
Greenwich, 1994; pp 89-160.
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A R T I C L E S
Itoh et al.
inset (a) in Figure 9 shows that the transient bands decay very
slowly and that it takes 5 s before all of the bands completely
3
disappear. The decay of 1 is found to be of the second order
(2k/ꢀl ) 0.65 s-1). The rough lifetime of 31 is estimated in the
form of the half-life, t1/2, to be 1.1 s. In accordance with the
kinetic observation, the MS analysis of the spent solution
indicates the presence of a peak at 1060.58 m/z, corresponding
to the dimer of the carbene as a major peak.20
A similar LFP of 2-2N2 again generated transient absorption
bands similar to those observed in the photolysis at 77 K (Figure
10). The fact that the molecular extinction coefficient of this
3
species is roughly 2 times as large as that observed for 1
5
indicates that the transient bands are due to 2 rather than to a
monocarbene generated by incomplete decomposition of 2-2N2.
This is further supported by the finding that analysis of the spent
solution by IR spectroscopy indicated the absence of a char-
acteristic band due to the diazo group. Again, the transient bands
decayed very slowly in a second-order fashion (2k/ꢀl ) 0.17
s-1), and the half-life, t1/2, was estimated to be 2.3 s.21
LFP of 3-3N2 generated transient bands similar to those
7
obtained in the photolysis at 77 K and ascribable to 3 based
on observations similar to those in the photolysis of 2-2N2
(Figure 11). The bands decayed in a second-order kinetic fashion
(2k/ꢀl ) 1.5 s-1) with a t1/2 of 1.2 s.22
Conclusion
The present investigation demonstrates that the preparation
of usable high-spin organic materials employing a triplet carbene
as a spin source is an achievable objective.
The finding that a precursor diazo unit can basically be
handled as a building block to construct polydiazo compounds
will make the project very realistic. Thus, one can introduce
the building block very easily on properly designed π-topologi-
cal linkers ad libitum. In other words, a polydiazo compound
designed to generate a desired high-spin polycarbene can be
prepared with great ease. A starburst nonadiazo compound, for
instance, was prepared by trimerization of aryl ethynyl ketone,
followed by oxidation, hydrazonation of the resulting nano-
ketone, and polyoxidation.5 The method is elegant, but it is
not applicable to other more complicated systems, including
sterically congested derivatives.
The study also reveals that persistent triplet carbenes, even
though they greatly lose typical reactivity as a triplet carbene,
still retain electronic properties and act as a spin source when
aligned properly in the π-electron frameworks to generate a
high-spin molecule, just as a prototypical triplet carbene does.
Figure 8. UV/vis spectra obtained by irradiation of tris(diazo) compound
3-3N2. (A) (a) Spectra of 3-3N2 in 2-methyltetrahydrofuran at 77 K. (b)
The same sample after irradiation (λ > 350 nm). (c) The same sample after
thawing to 150 K. (B) UV/vis spectral change measured at 10 K increments
upon thawing the same sample from 150 to 220 K.
in the conjugative manner usually show completely different
spectra with strong absorption bands in the visible region as a
result of extended conjugation of unpaired electrons in the π
framework.19 Upon thawing the matrix, the bands become
sharper, with a slight shift at around 100 K, and were observable
up to 170 K. Thus, the thermal stability of bis- and tris(carbenes)
is essentially identical to that of the monocarbene.
Time-Resolved UV/Vis Spectroscopic Study in Solution
at Room Temperature. To determine the stability of the present
carbenes more accurately, the lifetime was estimated in a
degassed benzene at room temperature, in which we measured
the lifetime of a series of sterically congested diarylcarbenes.6
Laser flash photolysis (LFP) of 1-N2 (1 × 10-4 M) in a
degassed benzene solution at room temperature with a 10 ns,
70-90 mJ, 308 nm pulse from a XeCl excimer laser produced
a transient species showing a strong absorption at 340, 358,
414, and 438 nm, which appeared coincident with the pulse
(Figure 9). The transient absorption bands are essentially the
same as those observed in the photolysis of 1-N2 in 2-MTHF
(20) The main decay pathway of those sterically congested diarylcarbenes
in benzene is coupling at the carbenic center. However, as the carbenic
center is more crowded, coupling at the aromatic rings where unpaired
electrons are delocalized becomes the more important process. See refs
6 and 10.
(21) The TOF-MS analysis of the spent solution indicates the presence of peaks
at 2109.16 m/z corresponding to the dimer of bis(carbene) 2 as a main
peak, along with weak peaks at 3163.74, 4218.32, 5272.90, 6325.48, and
7382.06 m/z, corresponding to the trimer, tetramer, pentamer, hexamer,
and heptamer of bis(carbene) 2, respectively. The peak at 2109.16 m/z is
well simulated by the dimer C158H156Si2. The intensities of the peaks at
higher oligomers decrease sharply with the increasing molecular weights
(see Figure 2S).
(22) The TOF-MS analysis of the spent solution indicates the presence of peaks
at 2919.79 m/z corresponding to the dimer of tris(carbene) 3 as a main
peak, along with weak peaks at 4385.25, 5619.18, 7254.25, and 8696.23
m/z, roughly corresponding to the trimer, tetramer, pentamer, and hexamer
of tris(carbene) 3, respectively. The intensities of the peaks at higher
oligomers decrease sharply with the increasing molecular weights (see
Figure 3S).
3
at 77 K. Thus, we assigned the transient product to 1. The
(19) (a) Harder, T.; Bendig, J.; Scholz, G.; Sto¨sser, R. J. Am. Chem. Soc.
1996, 118, 2497. (b) Serwinski, P. R.; Walton, R.; Sanborn, J. A.; Lahti,
P. M.; Enyo, T.; Miura, D.; Tomioka, H.; Nicolaides, A. Org. Lett. 2001,
3, 357.
9
1136 J. AM. CHEM. SOC. VOL. 126, NO. 4, 2004

Preparation of Oligodiazo Compounds
A R T I C L E S
Figure 9. Absorption of transient products formed during irradiation of monodiazo compound 1-N2 in degassed benzene at room temperature recorded 10
µs after excitation. The inset shows the time course of the absorption at 450 nm (oscillogram trace).
Figure 10. Absorption of transient products formed during irradiation of bis(diazo) compound 2-2N2 in degassed benzene at room temperature recorded 10
µs after excitation. The inset shows the time course of the absorption at 450 nm (oscillogram trace).
Most importantly, polycarbenes consisting of a persistent
triplet carbene are also very persistent, surviving up to 160 K
and a few seconds in solution at room temperature.23 Moreover,
undesirable bimolecular side reactions, which generate chemical
defects among the topologically controlled high-spin (S ) 1)
centers for extended spin alignment, are rigorously avoided.
Although high-spin organic materials with a lifetime of the
second order are still ephemeral for practical use, in the light
of the fact that a more persistent triplet carbene surviving days
under ambient conditions is close to being realized, it will not
be long before a stable high-spin polycarbene is available.24
Experimental Section
1
General Methods. H and 13C NMR spectra were recorded on a
JEOL JNM-AL300FT/NMR spectrometer in CDCl3 with Me4Si as an
internal reference. IR spectra were measured on a JASCO-Herschel
FT/IR-410 spectrometer, and UV-vis spectra were recorded on a
JASCO CT-560 spectrophotometer. The mass spectra were recorded
(23) All three species shown here decayed by a second-order fashion. In these
cases, the lifetime could not be determined and hence half-life, t1/2, was
used as a rough measure of the stability under these conditions. The half-
life is very much dependent upon the conditions, such as the concentration
of the species, and cannot be regarded as a definitive value to discuss the
stability in a quantitative manner. So the half-life reported here simply
indicated that the stability of three species may be roughly equal.
(24) It may be difficult to prepare a high-spin polycarbene consisting of the
present carbene unit because it has a fairly small D value mostly because
of the anthryl group. However, we have prepared an equally stable diazo
compound which not only survives a similar coupling reaction but also
can generate a triplet carbene with a larger D value.
9
J. AM. CHEM. SOC. VOL. 126, NO. 4, 2004 1137

A R T I C L E S
Itoh et al.
Figure 11. Absorption of transient products formed during irradiation of tris(diazo) compound 3-3N2 in degassed benzene at room temperature recorded 10
µs after excitation. The inset shows the time course of the absorption at 450 nm (oscillogram trace).
on a JEOL JMS-600H mass spectrometer. Gel permeation chromatog-
raphy (GPC) was carried out on a JASCO, model HLC-01 instrument
using UV-1570 as a detector. The GPC column was a Shodex H-2001.
Thin-layer chromatography was carried out on a Merck Kieselgel 60
PF254. Column chromatography was performed on silica gel (Fuji
Davidson) for column chromatography or ICN for dry column
chromatography.
Unless otherwise noted, all of the reagents employed in this study
are commercial products and used after standard purification. Tetrahy-
drofuran, ethyl ether, toluene, and dioxane were purified by distillation
from sodium/benzophenone, and dichloromethane, carbon tetrachloride,
and triethylamine were from calcium hydride.
mixture was washed with 20% aqueous potassium hydroxide, saturated
aqueous sodium thiosulfate, and water, and the organic layer was dried
over anhydrous sodium sulfate and concentrated under reduced pressure
to leave a residue which was reprecipitated with hexane to give 9-(4′-
tert-butyl-2′,6′-dimethyl)phenyl-10-bromoanthracene (3.3 g, 89%) as
a yellow solid: mp 180-181 °C; 1H NMR (300 MHz, CDCl3, ppm) δ
8.60-7.35 (m, 8H, Anth-H), 7.24 (s, 2H, Ph-H), 1.72 (s, 6H, -Me),
1.44 (s, 9H, -tBu); 13C NMR (75.5 MHz, CDCl3, ppm) δ 150.7, 136.8,
134.0, 130.6, 130.5, 128.0, 127.0, 126.5, 125.8, 124.5, 122.1, 124.4,
34.5, 31.5, 20.4; EI MS (m/z) 417.6 (base, M + 2), 415.6 (98.0, M+),
400.7 (32.3, M+ - Me). HRMS calcd for C26H25 416.1139, found m/z
416.1125.
Materials. 9-(4-tert-Butyl-2,6-dimethyl)phenylanthracene. To a
stirred solution of 4-tert-butyl-2,6-dimethylbromobenzene25 (5.0 g, 20.7
mmol) in dry ether (40 mL) was added dropwise a 1.50 M n-pentane
solution of tert-butyllithium (30.4 mL, 45.6 mmol) at -78 °C under
argon atmosphere. After being stirred for 1 h, the mixture was allowed
to warm to room temperature. A solution of anthrone26 (4.0 g, 20.7
mmol) in dry toluene (80 mL) was added dropwise to the mixture, and
the mixture was refluxed overnight. After being cooled to room
temperature and addition of saturated aqueous ammonium chloride (40
mL), the mixture was extracted with ether, and the organic layer was
washed with water, dried over anhydrous sodium sulfate, and concen-
trated under reduced pressure to leave a crude product which was
purified by column chromatography (silica gel, hexane), followed by
a short-path distillation (0.1 mmHg, 68 °C) to give 9-(4′-tert-butyl-
2′,6′-dimethyl)phenylanthracene (3.1 g, 44%) as a pale yellow solid:
[9-{10-(4-tert-Butyl-2,6-dimethyl)phenyl}anthryl](4-bromo-2,6-
dimethylphenyl)methanol. To a stirred solution of the bromoanthra-
cene (2.0 g, 4.8 mmol) in dry ether (40 mL) was added dropwise a
2.66 M hexane solution of n-butyllithium (2.2 mL, 5.8 mmol) at 0 °C
under argon atmosphere. After the mixture was stirred for 3 h, a solution
of 4-bromo-2,6-dimethylbenzaldehyde27 (1.0 g, 4.8 mmol) in dry
tetrahydrofuran (13 mL) was added dropwise to the mixture, and the
mixture was stirred at room temperature overnight. After addition of
saturated aqueous ammonium chloride (30 mL), the mixture was
extracted with ether, and the organic layer was washed with water,
dried over anhydrous sodium sulfate, and concentrated under reduced
pressure to leave a crude product which was purified by column
chromatography (silica gel, hexane:dichloromethane ) 2:1) to give
[9-{10-(4′-tert-butyl-2′,6′-dimethyl)phenyl}anthryl](4-bromo-2,6-di-
methylphenyl)methanol (2.0 g, 74%) as a yellow solid: mp 99.5-
1
1
mp 167 °C; H NMR (300 MHz, CDCl3, ppm) δ 8.47-7.29 (m, 9H,
100.0 °C; H NMR (300 MHz, CDCl3, ppm) δ 8.49-7.25 (m, 8H,
Anth-H), 7.24 (s, 2H, Ph-H), 1.73 (s, 6H, -Me), 1.44 (s, 9H, -tBu);
13C NMR (75.5 MHz, CDCl3, ppm) δ 150.3, 137.0, 136.0, 134.4, 131.6,
129.8, 128.6, 126.1, 126.0, 125.5, 125.1, 124.4, 34.5, 31.6, 20.4; EI
MS (m/z) 338.1 (base, M+), 323.2 (41.3, M+ - Me). HRMS calcd for
C26H26 338.2035, found m/z 338.2034.
Anth-H), 7.48 (s, 1H, HO-C-H), 7.24 (s, 2H, Anth-Ph-H), 7.18
(s, 2H, Ph-H), 2.41 (d, J ) 4.04 Hz, 1H, -OH), 2.18 (s, 6H, Ph-
Me), 1.72 (s, 6H, Anth-Ph-Me), 1.44 (s, 9H, -tBu); 13C NMR (75.5
MHz, CDCl3, ppm) δ 150.5, 139.3, 139.1, 138.1, 136.7, 134.7, 132.9,
132.7, 129.81, 129.76, 127.1, 125.9, 125.0, 124.7, 124.5, 120.8, 73.1,
34.5, 31.5, 21.8, 20.2.
9-(4-tert-Butyl-2,6-dimethyl)phenyl-10-bromoanthracene. To a
stirred solution of the phenylanthracene (3.1 g, 9.0 mmol) in carbon
tetrachloride (40 mL) was added bromine (0.5 mL, 9.0 mmol) at 0 °C.
The solution was stirred at room temperature overnight. The reaction
[9-{10-(4-tert-Butyl-2,6-dimethyl)phenyl}anthryl](4-bromo-2,6-
dimethylphenyl)chloromethane. Gaseous hydrochloric acid prepared
by adding hydrochloric acid (10 mL) to concentrated sulfuric acid (15
mL) was bubbled into a stirred solution of the methanol (1.5 g, 2.7
(25) Prisinzano, T.; Law, H.; Dukat, M.; Slassi, A.; MaClean, N.; Demchyshyn,
L.; Glennon, R. A. Bioorg. Med. Chem. 2001, 9, 613.
(26) Organic Syntheses; Wiley & Sons: New York, 1956; Collect. Vol. I, p
60.
(27) Yamakawa, M.; Kubota, T.; Akazawa, H. Bull. Chem. Soc. Jpn. 1967, 40,
1600.
9
1138 J. AM. CHEM. SOC. VOL. 126, NO. 4, 2004

Preparation of Oligodiazo Compounds
A R T I C L E S
mmol) in dry benzene (20 mL) for 1 h at 5 °C, and the reaction was
monitored by H NMR. The reaction mixture was concentrated and
[9-{10-(4-tert-Butyl-2,6-dimethyl)phenyl}anthryl](4-phenyl-2,6-
dimethylphenyl)diazomethane (1-N2). A mixture of the diazomethane
4 (50.0 mg, 0.09 mmol), palladium acetate (1.1 mg, 5.0 × 10-3 mmol),
potassium fluoride (19 mg, 0.33 mmol), 2-(di-tert-butylphosphino)-
biphenyl (4.5 mg, 1.5 × 10-2 mmol), benzene boronic acid (18.3 mg,
0.15 mmol), and dry tetrahydrofuran (0.5 mL) was stirred overnight at
40 °C under nitrogen atmosphere. The reaction mixture was passed
through a short alumina column, and the filtrate was concentrated and
dried under reduced pressure to leave a crude product which was
purified by GPC (chloroform, monitored at 350 nm) to afford 1-N2
(44 mg, 88%) as an orange solid: mp 135.0-140.5 °C (dec); 1H NMR
(300 MHz, CDCl3, ppm) δ 8.10 (d, J ) 8.82 Hz, 2H), 7.62 (d, J )
7.35 Hz, 2H), 7.54-7.30 (m, 13H), 2.24 (s, 6H, H), 1.75 (s, 6H); 13C
NMR (75.5 MHz, CDCl3, ppm) δ 150.5, 140.6, 139.9, 137.9, 137.3,
136.9, 134.4, 130.3, 130.1, 129.8, 128.7, 128.1, 127.2, 127.2, 126.9,
126.3, 125.40, 125.36, 124.5, 123.5, 57.5, 34.5, 31.6, 21.5, 20.3; IR
1
dried under reduced pressure to give [9-{10-(4′-tert-butyl-2′,6′-dimethyl)-
phenyl}anthryl](4-bromo-2,6-dimethylphenyl)chloromethane (1.5 g,
97%) as a yellow solid: 1H NMR (300 MHz, CDCl3, ppm) δ 8.49-
7.26 (m, 8H, Anth-H), 7.78 (s, 1H, Cl-C-H), 7.24 (s, 2H, Anth-
Ph-H), 7.21 (s, 2H, Ph-H), 2.31 (s, 6H, Ph-Me), 1.72 (s, 6H, Anth-
Ph-Me), 1.44 (s, 9H, -tBu); 13C NMR (75.5 MHz, CDCl3, ppm) δ
150.6, 139.7, 139.2, 137.1, 136.7, 134.5, 133.0, 129.9, 129.7, 128.3,
127.3, 126.1, 125.0, 124.8, 124.5, 121.6, 59.4, 34.5, 31.5, 22.4, 20.3.
Ethyl N-[9-{10-(4-tert-Butyl-2,6-dimethyl)phenyl}anthryl](4-
bromo-2,6-dimethylphenyl)carbamate. A mixture of ethyl carbamate
(4.6 g, 51.6 mmol) and silver tetrafluoroborate (0.6 g, 2.8 mmol) was
heated to 60 °C. A solution of the chloromethane (1.5 g, 2.6 mmol) in
dry dioxane (13 mL) was added dropwise to this mixture at the same
temperature. After being refluxed overnight, the reaction mixture was
filtered and the filtrate was extracted with chloroform, and the organic
layer was washed with water, dried over anhydrous sodium sulfate,
and concentrated under reduced pressure to leave a crude product which
was column chromatographed (silica gel, hexane:dichloromethane )
1:1) to give ethyl N-[9-{10-(4′-tert-butyl-2′,6′-dimethyl)phenyl}anthryl]-
(4-bromo-2,6-dimethylphenyl)carbamate (1.2 g, 75%) as a pale brown
solid: mp 136.6-137.2 °C; 1H NMR (300 MHz, CDCl3, ppm) δ 8.31-
7.27 (m, 8H, Anth-H), 7.54 (d, J ) 9.00 Hz, 1H, N-C-H), 7.24 (s,
2H, Anth-Ph-H), 7.13 (s, 2H, Ph-H), 5.47 (d, J ) 8.64 Hz, 1H,
-NH), 4.22 (q, J ) 7.17 Hz, 2H, -CH2-), 2.17 (s, 6H, Ph-Me),
1.70 (s, 6H, Anth-Ph-Me), 1.43 (s, 9H, -tBu), 1.26 (d, J ) 7.17 Hz,
3H, -CH2-Me); 13C NMR (75.5 MHz, CDCl3, ppm) δ 155.4, 150.5,
138.7, 138.3, 138.2, 136.7, 134.5, 133.1, 129.8, 129.7, 127.3, 126.4,
125.0, 124.5, 123.7, 120.1, 61.4, 53.8, 34.5, 31.5, 22.5, 20.3, 14.7.
(KBr, cm-1) νCdN 2039.
2
3,5-Bis{3,5-dimethyl-4-(diazo[9-{10-(4-tert-butyl-2,6-dimethyl)-
phenyl}anthryl]methyl)phenyl} Benzene (2-2N2). A mixture of the
diazomethane 4 (28 mg, 0.05 mmol), palladium acetate (0.6 mg, 3 ×
10-3 mmol), potassium fluoride (9.5 mg, 0.15 mmol), 2-(di-tert-
butylphosphino)biphenyl (2.3 mg, 8 × 10-3 mmol), 5-trimethylsilyl-
benzene-1,3-diboronic acid (5.9 mg, 0.025 mmol), and dry tetrahydro-
furan (0.3 mL) was stirred overnight at 40 °C under nitrogen
atmosphere. The reaction mixture was passed through a short alumina
column, and the filtrate was concentrated and dried under reduced
pressure to leave a crude product which was purified by GPC
(chloroform, monitored at 350 nm) to afford bis(diazo) compound 2-2N2
1
(14 mg, 51%) as an orange solid: mp 150-155.0 °C (dec); H NMR
(300 MHz, CDCl3, ppm) δ 8.11 (d, J ) 8.64 Hz, 4H), 7.80 (s, 1H),
7.71 (s, 2H), 7.60-7.20 (m, 26H), 2.26 (s, 12H), 1.75 (s, 12H), 1.44
(s, 18H), 0.36 (s, 9H); 13C NMR (75.5 MHz, CDCl3, ppm) δ 151.5,
142.6, 141.4, 141.2, 138.9, 138.4, 137.8, 135.4, 131.8, 131.3, 131.1,
130.8, 129.2, 129.1, 128.1, 127.5, 127.2, 126.3, 125.4, 124.4, 58.4,
Ethyl N-Nitroso-N-[9-{10-(4-tert-butyl-2,6-dimethyl)phenyl}-
anthryl]{(4-bromo-2,6-dimethylphenyl)methyl}carbamate. Nitrogen
dioxide (5.0 g) was bubbled into dry carbon tetrachloride (20 mL) at
-20 °C under stirring. Sodium acetic acid (9.0 g, 109.7 mmol) and a
solution of the carbamate (1.2 g, 1.9 mmol) in dry carbon tetrachloride
(15 mL) were added to the mixture. The mixture was allowed to warm
to room temperature for 2 h and was poured into ice. This mixture
was extracted with chloroform, and the organic layer was washed with
water, dried over anhydrous sodium sulfate, concentrated, and dried
under reduced pressure to give ethyl N-nitroso-N-[9-{10-(4′-tert-butyl-
2′,6′-dimethyl)phenyl}anthryl]{(4-bromo-2,6-dimethylphenyl)methyl}-
carbamate (1.4 g, quant.) as a yellow solid; 1H NMR (300 MHz, CDCl3,
ppm) δ 7.89 (s, 1H, N-C-H), 7.63-7.22 (m, 8H, Anth-H), 7.24 (s,
2H, Anth-Ph-H), 7.16 (s, 2H, Ph-H), 4.11 (q, J ) 7.17 Hz, 2H,
-CH2-), 1.96 (s, 6H, Ph-Me), 1.70 (s, 6H, Anth-Ph-Me), 1.44 (s,
9H, -tBu), 0.81 (d, J ) 7.17 Hz, 3H, -CH2-Me); 13C NMR (75.5
MHz, CDCl3, ppm) δ 153.6, 150.6, 139.1, 138.3, 136.6, 134.9, 134.5,
133.0, 130.7, 129.6, 127.3, 126.55, 126.45, 125.0, 124.5, 123.5, 121.0,
64.3, 56.4, 34.5, 31.5, 20.9, 20.2, 13.4.
35.4, 32.5, 22.4, 21.3, 1.0; IR (KBr, cm-1) νCdN 2039.
2
1,3,5-Tris{3,5-dimethyl-4-(diazo[9-{10-(4-tert-butyl-2,6-dimethyl)-
phenyl}anthryl]methyl)phenyl}benzene (3-3N2). A mixture of the
diazomethane 4 (56 mg, 0.1 mmol), palladium acetate (0.1 mg, 5 ×
10-4 mmol), potassium phosphate (42 mg, 0.2 mmol), tetra(butyl)-
ammonium bromide (cat.) and benzene triboronic acid28 (6.3 mg, 0.03
mmol), and dry DMF (0.5 mL) was stirred overnight at 40 °C under
nitrogen atmosphere. The reaction mixture was passed through a short
alumina column, and the filtrate was concentrated and dried under
reduced pressure to leave a crude product which was purified by GPC
(chloroform, monitored at 350 nm) to afford tris(diazo) compound 3-3N2
1
(10.4 mg, 20%) as an orange solid: mp 291-297 °C (dec); H NMR
(300 MHz, CDCl3, ppm) δ 8.11 (d, J ) 8.82 Hz, 6H), 7.82 (s, 3H),
7.54-7.30 (m, 30H), 2.27 (s, 18H), 1.75 (s, 18H), 1.44 (s, 27H); 13C
NMR (75.5 MHz, CDCl3, ppm) δ 150.5, 141.7, 139.8, 137.9, 137.5,
136.8, 134.4, 130.3, 130.14, 130.10, 128.2, 127.2, 126.3, 125.4, 125.3,
124.7, 124.5, 123.5, 57.5, 34.5, 31.6, 21.5, 20.3; IR (KBr, cm-1) νCdN
[9-{10-(4-tert-Butyl-2,6-dimethyl)phenyl}anthryl](4-bromo-2,6-
dimethylphenyl)diazomethane (4). To a stirred solution of the nitroso-
carbamate (1.4 g, 2.2 mmol) in dry tetrahydrofuran (15 mL) was added
potassium tert-butoxide (0.5 mg, 4.7 mmol) at -20 °C under argon
atmosphere. After being stirred overnight, the reaction mixture was
poured into ice, extracted with ether, and the ethereal layer was washed
with water, dried over anhydrous sodium sulfate, concentrated, and
dried under reduced pressure to leave a crude product which was
purified by column chromatography (alumina, hexane at -20 °C),
followed by GPC (chloroform, monitored at 350 nm) to give 4 (0.6 g,
48%) as an orange solid: 1H NMR (300 MHz, CDCl3, ppm) δ 8.00-
7.25 (m, 8H, Anth-H), 7.28 (s, 2H, Ph-H), 7.25 (s, 2H, Anth-Ph-
H), 2.14 (s, 6H, Ph-Me), 1.73 (s, 6H, Anth-Ph-Me), 1.44 (s, 9H,
-tBu); 13C NMR (75.5 MHz, CDCl3, ppm) δ 150.6, 138.9, 138.1, 136.8,
134.3, 132.0, 130.2, 130.1, 129.9, 127.2, 126.4, 125.4, 125.1, 124.5,
122.7, 120.8, 57.1, 34.5, 31.5, 21.1, 20.3; IR (KBr, cm-1) νCdN2 2041.
2
2039.
5-Trimethylsilylbenzene-1,3-diboronic Acid Dipinacol Ester. A
mixture of 5-trimethylsilyl-1,3-dibromobenzene29 (1.0 g, 3.3 mmol),
diborane pinacol ester (1.8 g, 7.2 mmol), PdCl2(dppf) (150 mg, 0.2
mmol), KOAc (220 mg, 19.5 mmol), and DMSO (20 mL) was heated
to 80 °C for 4 h. After the mixture was cooled, water (50 mL) was
added, and the mixture was extracted with CH2Cl2. The organic layer
was washed with brine, dried over Na2SO4, and the solvent was
evaporated. The residue was passed through a short alumina column
and then purified by GPC (CHCl3, monitored at 250 nm) to give
5-trimethylsilylbenzene-1,3-diboronic acid dipinacol ester as a light
1
brown solid (990 mg, 76%): mp 125-128 °C; H NMR (300 MHz,
(28) Morgan, A. B.; Jurs, J. L.; Tour, J. M. J. Appl. Polym. Sci. 2000, 76, 1257.
(29) Daniel, R. J. D.; Burghard, Z.; Guenter, S. Eur. J. Org. Chem. 1999, 9,
2079.
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J. AM. CHEM. SOC. VOL. 126, NO. 4, 2004 1139

A R T I C L E S
Itoh et al.
CDCl3, ppm) δ 8.26 (s, 1H), 8.04 (s, 2H), 1.34 (s, 24H), 0.29 (s, 9H);
13C NMR (75.5 MHz, CDCl3, ppm) δ 143.5, 142.9, 141.3, 139.4, 84.6,
26.0, 1.0; EI MS (m/z) 402 (4.4%, M+), 387 (61%, M+ - Me), 84
(100%).
5-Trimethylsilylbenzene-1,3-diboronic Acid. To a solution of the
ester (201 mg, 0.5 mmol) in acetone (30 mL) were added NaIO4 (641
mg, 3.0 mmol), NH4OAc (231 mg, 3.0 mmol), and water (15 mL),
and the mixture was stirred for 48 h. Acetone was evaporated, and the
mixture was extracted with ether, the ethereal solution was dried over
Na2SO4, and the solvent was evaporated and dried in vacuo to give
5-trimethylsilylbenzene-1,3-diboronic acid as a light brown solid (95
mg, 80%): mp 164-168 °C.
EPR Measurements. The diazo compound was dissolved in
2-methyltetrahydrofuran (10-3 M), and the solution was degassed in a
quartz cell by three freeze-degas-thaw cycles. The sample was cooled
in an optical transmission EPR cavity at 77 K and irradiated with a
Wacom 500 W Hg lamp using a cutoff filter (λ > 350 nm). EPR spectra
were measured on a JEOL JES TE 200 spectrometer (X-band
microwave unit, 100 kHz field modulation). The signal positions were
read by the use of a gaussmeter. The temperature was controlled by a
9650 Microprocessor-based Digital Temperature Indicator/Controller,
which provided the measurements with an accuracy within (0.1 K
and a control ability within (0.2 K. Errors in the measurements of
component amplitudes did not exceed 5%, and the accuracy of the
resonance fields determination was within (0.5 mT.
Low-Temperature UV/Vis Spectra. Low-temperature spectra at 77
K were obtained by using an Oxford variable-temperature liquid-
nitrogen cryostat (DN 1704) equipped with a quartz outer window and
a sapphire inner window. The sample was dissolved in dry 2-MTHF,
placed in a long-necked quartz cuvette of 1 mm path length, and
degassed thoroughly by repeated freeze-degas-thaw cycles at a
pressure near 10-5 Torr. The cuvette was flame-sealed, under reduced
pressure, placed in the cryostat, and cooled to 77 K. The sample was
irradiated for several minutes in the spectrometer with a Halos 300 W
high-pressure mercury lamp using a cutoff filter (λ > 350 nm), and
the spectral changes were recorded at the appropriate time intervals.
The spectral changes upon thawing were also monitored by carefully
controlling the matrix temperature with an Oxford Instrument Intelligent
Temperature Controller (ITC 4).
fiber scope, was arranged in an orientation perpendicular to the
excitation source. The probe beam was monitored with a Hamamatsu
R2949 photomultiplier tube through a Hamamatsu S3701-512Q MOS
linear image sensor (512 photodiodes used). Timing of the excitation
pulse, the probe beam, and the detection system was achieved through
an Iwatsu model DS-8631 digital synchro scope which was interfaced
to a NEC 9801 RX2 computer. This allowed for rapid processing and
storage of the data and provided printed graphic capabilities. Each trace
was also displayed on a NEC CRT N5913U monitor.
A sample was placed in a long-necked Pyrex tube which had a
sidearm connected to a quartz fluorescence cuvette and was degassed
using a minimum of four freeze-degas-thaw cycles at a pressure near
10-5 Torr immediately prior to being flashed. The sample system was
flame-sealed under reduced pressure, and the solution was transferred
to the quartz cuvette which was placed in the sample chamber of the
flash spectrometer. A cell holder block of the sample chamber was
equipped with a thermostat and allowed to come to thermal equilibrium.
The concentration of the sample was adjusted so that it absorbed a
significant portion of the excitation light.
SQUID Measurements. Magnetic susceptibility data were obtained
on a Quantum Design MPMS-2A superconducting quantum interference
device (SQUID) magnetometer/susceptometer. Irradiation with light
from an argon ion laser (488 nm, Omnichrome 543-150BS) through a
flexible optical fiber which passes through the inside of the SQUID
sample holder was performed inside the sample room of the SQUID
apparatus at 5-11 K. One end of the optical fiber was located 40 mm
above the sample cell (capsule), and the other was attached to a coupler
for the laser. The bottom part of the capsule (6 mm × 10 mm) without
a cap was used as a sample cell. A 80 µL sample of the solution (1.0
mM) in 2-MTHF was placed in the cell, which was held by a straw.
The irradiation was carried out until there was no further change of
magnetization monitored at 5 K in a constant field of 5 KOe. The
magnetization, Mb and Ma, before and after irradiation was measured
at 2 and 5 K in a field range 0-50 kOe. The plots of the magnetization
[M ) (Ma - Mb): F stands for a photolysis factor of diazo compound]
versus the magnetic field were analyzed in terms of the Brillouin
function.
Acknowledgment. The authors are grateful to the Ministry
of Education, Culture, Sports, Science, and Technology of Japan
for support of this work through a Grant-in-Aid for Scientific
Research for Specially Promoted Research (No. 12002007).
Support from the Mitsubishi Foundation and the Nagase Science
and Technology Foundation is also appreciated.
Flash Photolysis. All flash measurements were made on a Unisoku
TSP-601 flash spectrometer. Three excitation light sources were used
depending on the precursor absorption bands and lifetime of the transient
species. They were (i) a cylindrical 150-W Xe flash lamp (100 J/flash
with 10 ms pulse duration), (ii) a Quanta-Ray GCR-11 Nd:YAG laser
(355 nm pulses of up to 40 mJ/pulse and 5-6 ns duration; 266 nm
pulses of up to 30 mJ/pulse and 4-5-ns duration), and (iii) a Lamda
Physik LEXTRA XeCl excimer laser (308 nm pulses of up to 200 mJ/
pulse and 17 ns duration). The beam shape and size were controlled
by a focal length cylindrical lens.
Supporting Information Available: MS spectra (PDF). This
material is available free of charge via the Internet at
http://pubs.acs.org.
A Hamamatsu 150 W xenon short arc lamp (L 2195) was used as
the probe source, and the monitoring beam, guided using an optical
JA038450P
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1140 J. AM. CHEM. SOC. VOL. 126, NO. 4, 2004