Preparation of bis(diazo) compounds incorporated into butadiyne and thiophene units, and generation and characterization of Bis(carbene) from these compounds

Article abstract of DOI:10.1021/jo0494026

[9-{10-(4-t-Butyl-2,6-dimethyl)phenyl}anthryl](4-bromo-2,6-dimethylphenyl) diazomethane(1-N₂) was found to be stable enough to survive under Sonogashira and Suzuki coupling reaction conditions, and bis(diazo) compounds incorporated into the 1,4

Full text of DOI:10.1021/jo0494026

P r ep a r a tion of Bis(d ia zo) Com p ou n d s In cor p or a ted in to
Bu ta d iyn e a n d Th iop h en e Un its, a n d Gen er a tion a n d
Ch a r a cter iza tion of Bis(ca r ben e) F r om Th ese Com p ou n d s
Tetsuji Itoh,† Fumika Morisaki,† Katsuyuki Hirai,‡ and Hideo Tomioka*,†
Chemistry Department for Materials, Faculty of Engineering, and Instrumental Analysis Facilities,
Life Science Research Center, Mie University, Tsu, Mie 514-8507, J apan
tomioka@chem.mie-u.ac.jp
Received April 9, 2004
[9-{10-(4-t-Butyl-2,6-dimethyl)phenyl}anthryl](4-bromo-2,6-dimethylphenyl)diazomethane (1-N2)
was found to be stable enough to survive under Sonogashira and Suzuki coupling reaction conditions,
and bis(diazo) compounds incorporated into the 1,4-positions of butadiyne (3-2N2) and the 2,5-
position of thiophene (4-2N2) were prepared. Irradiation of those bis(diazo) compounds generated
bis(carbenes), which were characterized by ESR and UV-vis spectroscopic techniques in a matrix
at low temperature, as well as time-resolved UV-vis spectroscopy in solution at room temperature.
These studies revealed that both of the bis(carbenes), 3 and 4, have a singlet quinoidal diradical
ground state with a very small singlet-triplet energy gap of less than 1 kcal/mol. A remarkable
increase in the lifetime of bis(carbenes) as opposed to that of monocarbene (1) was noted and was
interpreted to indicate that bis(carbenes) are thermodynamically stabilized as a result of
delocalization of unpaired electrons throughout a π-net framework. Despite the stability, both bis-
(carbenes) are readily trapped by molecular oxygen to afford bis(ketones) as main products.
A diazo compound1 is an excellent precursor for a
carbene and, hence, has been widely employed to gener-
ate and study carbenes.2 Upon either heating or irradia-
tion, it decomposes very efficiently and cleanly to elimi-
nate nitrogen gas and leave only the carbene. Moreover,
the reaction occurs even at very low temperatures in the
solid phase, which makes the spectroscopic study of a
carbene very easy. However, because of the inherent
sensitivity of the diazo functional group, not only to heat
or light but also to an acid or metal, this group is usually
introduced at the last step of synthesis, which sometimes
makes the usability of the group rather limited.
ethynylphenyl)diazomethane.4 It is both interesting and
important to explore the applicability of this method, as
it may open a door to a new route to organic magnetic
materials. This report shows that the diaryldiazo unit
can be connected to a butadiyne unit by an oxidative
coupling reaction5 of acetylene and to the thiophene ring
by the Suzuki coupling reaction.6 The characterization
of the bis(carbene) generated from those bis(diazo) com-
pounds is also reported.
Resu lts
P r ep a r a tion of Bis(d ia zo) Com p ou n d s. The start-
ing diazo compound used in this study was [9-{10-(4-t-
butyl-2,6-dimethyl)phenyl}anthryl](4-bromo-2,6-dimeth-
ylphenyl)diazomethane (1-N2), which was prepared
according to the procedure outlined in Scheme 1; this
compound can generate a fairly persistent triplet car-
bene.7,8 Treatment of 1-N2 with trimethylsilylacetylene
in the presence of (Ph3P)2PdCl2 and CuI at 40 °C for 2
days gave [9-{10-(4-t-butyl-2,6-dimethyl)phenyl}anthryl]-
(4-t r im et h ylsilylet h yn yl-2,6-dim et h ylph en yl)dia zo-
methane (2-N2) in 74% yield. Deprotection9 of the TMS
We found, more or less by chance, that a diphenyl-
diazomethane that has been prepared to generate a
persistent triplet carbene is also persistent for a diazo
compound and, hence, can be further modified into a
more complicated diazo compound, leaving the diazo
group intact. For instance, bis(2,4,6-tribromophenyl)diazo-
methane survives under Sonogashira coupling reaction
conditions,3 leading to bis(2,6-dibromo-4-trimethylsilyl-
† Chemistry Department for Materials.
‡ Instrumental Analysis Facilities.
(1) Regitz, M.; Maas, G. Diazo CompoundssProperties and Synthe-
sis; Academic Press: Orlando, FL, 1986.
(2) For reviews of general reactions of carbenes, see: (a) Kirmse,
W. Carbene Chemistry, 2nd ed.; Academic Press: New York, 1971. (b)
Carbenes; Moss, R. A., J ones, J r., M., Eds.; Wiley: New York, 1973
and 1975; Vols. 1 and 2. (c) Carbene(oide), Carbine; Regitz, M., Ed.;
Thieme: Stuttgart, Germany, 1989.
(3) Sonogashira, K. In Comprehensive Organic Synthesis; Trost, B.
M., Fleming, I., Eds.; Pergamon Press: Oxford, U.K., 1991; Vol. 3, pp
521-549.
(4) Tomioka, H.; Hattori, M.; Hirai, K.; Sato, K.; Shiomi, D.; Takui,
T.; Itoh, K. J . Am. Chem. Soc. 1998, 120, 1106.
(5) Hay, A. S. J . Org. Chem. 1960, 25, 1275; 1962, 27, 3320. See
also: Montierth, J . M.; DeMario, D. R.; Kurth, M. J .; Schore, N. E.
Tetrahedron 1998, 54, 11741.
(6) For reviews, see for example: (a) Suzuki, A. In Metal-Catalyzed
Cross-Coupling Reactions; Diederich, F., Stang, P. J ., Eds.; Wiley-
VCH: Weinheim, Germany, 1998; pp 49-97. (b) Stanforth, S. P.
Tetrahedron 1998, 54, 263.
10.1021/jo0494026 CCC: $27.50 © 2004 American Chemical Society
Published on Web 08/03/2004
5870
J . Org. Chem. 2004, 69, 5870-5880

Preparation of Bis(diazo) Compounds
SCHEME 1
SCHEME 2
SCHEME 3
group with NaOH proceeded smoothly to give an ethynyl
derivative in 80% yield. Stirring a mixture of ethynylated
diazomethane and CuCl(OH)-TMEDA in CH2Cl2 under
air5 for 6 h at room temperature gave a bis(diazo)
butadiyne compound (3-2N2) in 57% yield (Scheme 2).
1H NMR spectra of 3-2N2 showed no acetylenic protons,
and 13C NMR spectra showed the presence of acetylenic
carbons at 81.8 and 74.4 ppm, which are shifted from
105.1 and 94.5 ppm in 2-N2. This NMR evidence sug-
gests that acetylenic protons are lost while the acetylene
bonds remain and are likely connected to carbons.
Because diazo functional groups are not persistent
enough to survive ionization processes during MS mea-
surements, direct MS measurements were not possible.
So, we photolyzed 3-2N2 in the presence of oxygen and
analyzed the products by NMR and MS. From the
reaction mixtures, we were able to isolate the diketone
(3-2O) as the main product.
Attempts to convert the butadiyne portion of 3-2N2
to the thiophene ring by treatment with Na2S‚9H2O10 in
THF at 50 °C for 20 h resulted in the formation of a
complex reaction mixture.
However, treatment of 1-N2 with thiophene diboronic
acid under Suzuki coupling conditions6 (i.e., in the
presence of Pd(OAc)2 as a catalyst, P(tBu)2(2-BP) (2-BP )
2-biphenylyl) as a ligand, and KF as a base in THF at
40 °C) gave 2,5-bis(3,5-dimethyl-4-[9-{10-(4-t-butyl-2,6-
dimethyl)phenyl}anthryl]diazomethylphenyl)thiophene
(4-2N2) (Scheme 3). Again, irradiation of 4-2N2 in the
presence of oxygen gave bis(ketone) 4-2O as main
product.
All of the procedures were carried out in the dark, and
compounds were purified either by silica gel chromatog-
raphy at ca. 0 °C and/or by repeated chromatography on
a gel permeation column. No appreciable decomposition
of the diazo group was noted, at least under the condi-
tions employed here.
(7) For studies of anthrylcarbenes, see: (a) Wasserman, E.; Kuck,
V. J .; Yager, W. A.; Hutton, R. S.; Greene, F. D.; Abegg, V. P.;
Weinshenker, N. M. J . Am. Chem. Soc. 1971, 93, 6335. (b) Astles, D.
J .; Girard, M.; Griller, D.; Kolt, J .; Wayner, D. D. J . Org. Chem. 1998,
53, 6053. (c) Itakura, H.; Tomioka, H. Org. Lett. 2000, 2, 2995. (d)
Takahashi Y.; Tomura, M.; Yoshida, K.; Murata, S.; Tomioka, H.
Angew. Chem., Int. Ed. 2000, 39, 3478. (e) Tomioka, H.; Iwamoto, E.;
Itakura, H.; Hirai, K. Nature 2001, 412, 6847. (f) Iwamoto, E.; Hirai,
K.; Tomioka, H. J . Am. Chem. Soc. 2003, 125, 14664.
(8) See for review of persistent triplet carbenes: (a) Tomioka, H.
Acc. Chem. Res. 1997, 30, 315. (b) Tomioka, H. In Advances in Carbene
Chemistry; Brinker, U., Ed.; J AI Press: Greenwich, CT, 1998; Vol. 2,
pp 175-214. (c) Tomioka, H. In Carbene Chemistry; Bertrand G., Ed.;
FontisMedia: Lausanne, Switzerland, 2002; pp 103-152.
The results showed that the protected diazo compound
is fairly persistent, and it can be used as a building block
(9) Hurst, D. T.; McInnes, A. G. Can. J . Chem. 1965, 43, 2004.
(10) Kagan, J .; Arora, S. K. J . Org. Chem. 1983, 48, 4317.
J . Org. Chem, Vol. 69, No. 18, 2004 5871

Itoh et al.
F IGURE 1. ESR spectra obtained by irradiation of monodiazo
compound 2-N2 in 2-methyltetrahydrofuran at 77 K. The
microwave frequency (ν0) was 9.1327 GHz.
to construct a new poly(diazo) derivative from which a
new magnetic system may be derived.
The characterization of the structure of the bis(car-
bene) expected to be generated upon photolysis of those
bis(diazo) precursors is of great importance in view of
recent, growing interest in spin molecules.11,12 Thus, the
products obtained by the photolysis of bis(diazo) com-
pounds, 3-2N2 and 4-2N2, were characterized by ESR
and UV-vis spectroscopy and compared with those from
the corresponding mono-derivatives, 2-N2.
Sp ectr oscop ic Stu d ies. ESR Stu d ies. Irradiation of
monodiazomethane 2-N2 in 2-methyltetrahydrofuran (2-
MTHF) at 77 K gave ESR signals with typical fine
structure patterns for nonoriented triplet species, i.e., 32
(Figure 1).13 The signals at 202, 214, 408, and 417 mT
are assigned to a set of x and y transitions, and the signal
at 523 mT is assigned to a high-field z transition from
which the zero-field splitting (ZFS) parameters were
obtained as |D/hc| ) 0.192 cm-1 and |E/hc| ) 0.002 75
cm-1. The values are similar to those observed for a series
of triplet anthryl(aryl)carbenes.7,14 The other signal at
112 mT is assigned to ∆ms ) (2 transitions.
F IGURE 2. (a) ESR spectra obtained by irradiation of bis-
(diazo) compound 3-2N2 in 2-methyltetrahydrofuran at 70 K
(ν0 ) 9.1320 GHz). (b-f) The same spectra observed at 6 (b),
80 (c), 90 (d), 180 (e), and 260 (f) K. (g) Simulated spectra of
33 with S ) 1, g ) 2.003, |D/hc| ) 0.0474 cm-1, |E/hc| ) 0 cm-1
,
3
and line width (∆B) of 68 G. (h) Simulated spectra of 3 with
S ) 1, g ) 2.003, |D/hc| ) 0.0306 cm-1, |E/hc| ) 0.00 cm-1
and ∆B ) 18 G. Signals marked with asterisks (*) are due to
a monocarbene.
,
Similar irradiation of a bis(diazo) compound (3-2N2)
connected by a butadiyne bond in 2-MTHF at 70 K gave
ESR signals (Figure 2a)that are different from those
observed for the corresponding monocarbene, 32. The
pattern of signals did not change from the initial to the
latter stages of irradiation. The signals at 116, 206, and
3
412 mT are similar to those observed for 2 and, hence,
(11) See for review: (a) Rajca, A. Chem. Rev. 1994, 94, 871. (b)
Iwamura, H. Adv. Phys. Org. Chem. 1990, 26, 179. (c) Magnetic
Properties of Organic Materials; Lahti, P. M., Ed.; Marcel Dekker: New
York, 1999.
are attributable to a monocarbene presumably formed
because of incomplete decomposition of 3-2N2. The weak
signals appearing from 298 to 352 mT are obviously
different from those of the monocarbene triplet and are
ascribable to bis(carbene), 3. The major signals are
reproduced well by computer simulation,15,16 as shown
in Figure 2g, employing a triplet Hamiltonian with S )
(12) (a) Kahn, O. Molecular Magnetism; VCH Publishers: Weinheim,
Germany, 1993. (b) Gatteschi, D. Adv. Mater. (Weinheim, Ger.) 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,
73 (Oct 2), 30. (e) Magnetism: A Supramolecular Function; Kahn, O.,
Ed.; NATO ASI Series C; Kluwer: Dordrecht, The Netherlands, 1996.
(f) Molecule-Based Magnetic Materials; Turnbull, M. M., Sugimoto, T.,
Thompson, L. K., Eds.; ACS Symposium Series 644; American Chemi-
cal Society: Washington, DC, 1996. (g) Gatteschi, D. Curr. Opin. Solid
State Mater. Sci. 1996, 1, 192. (h) Miller, J . S.; Epstein, A. J . MRS
Bull. 2000, 25, 21. (i) Magnetism: Molecules to Materials II; Miller, J .
S., Drillon, M., Eds.; Wiley-VCH: New York, 2001. (j) Molecular
Magnetism; Itoh, K., Kinoshita, M., Eds.; Kodansha-Gordon and
Breach: Tokyo, 2000.
(13) 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; J ones, M., J r., Moss, R.
A., Eds.; Wiley: New York, 1975; Vol. 2, pp 185-206.
(14) See also: Tomioka, H. In Advances in Strained and Interesting
Organic Molecules; Halton, B., Ed.; J AI Press: Greenwich, CT, 2000;
Vol. 8, pp 83-112.
1, g ) 2.003, |D/hc| ) 0.0474 cm-1, and |E/hc| ≈ 0 cm-1
.
Therefore, we assigned the new, fine-structured peaks
to a triplet state of bis(carbene), most probably in its
quinoidal form. Cooling the sample to 6 K resulted in a
marked decrease of the signal (Figure 2c), but the signal
was regained when the matrix was warmed. When the
2-MTHF glass was warmed to ∼90 K, a new set of triplet
(15) Teki, Y. Ph.D. Thesis, Osaka City University, Osaka, J apan,
1985.
(16) Takui, K. In Molecular Magnetism in Organic-Based Materials;
Lahti, P. M., Ed.; Marcel Dekker: New York, 1999.
5872 J . Org. Chem., Vol. 69, No. 18, 2004

Preparation of Bis(diazo) Compounds
3
F IGURE 3. Plots of the intensities of the ESR signals (a) at 298 mT due to thermally populated 3 vs reciprocal of temperature
(6-75 K), and (b) at 340 mT due to thermally populated 34 vs reciprocal of temperature (4.3-70 K).
peaks (|D/hc| ) 0.0306 cm-1, |E/hc| ≈ 0 cm-1) appeared
at the expense of the original peaks (Figure 1d). These
changes were not reversible: When the sample was
cooled to 70 K, no change took place. Changes of this kind
have often been observed for sterically congested triplet
diarylcarbenes and are usually interpreted in terms of
geometrical changes. The intensity of the signals in-
creased up to 90 K and started to decrease above this
temperature. The signals continued to decrease until all
of the signals disappeared irreversibly when the tem-
perature was raised to 260 K (Figure 2f). No signals
attributable to the quintet state were observed during
the temperature studies.
The decreasing intensity of the signals at <30 K and
the recovery of the signals upon warming of the matrix
clearly indicate that the signals are due to a thermally
populated excited state. Actually, the plot of intensity of
the signals at 298 mT versus the temperature from 6 to
75 K deviated from the Curie-Weiss law (Figure 3a).
The temperature dependence of the ESR signal inten-
sity for 3 indicates that the quinoidal form of bis(carbene)
has a singlet ground state. To determine the singlet-
triplet energy gap (∆ET-S ) 2J ) of quinoidal bis(carbene),
the observed data were analyzed in terms of the Bleaney-
Bowers-type thermal distribution17
F IGURE 4. (a) ESR spectra obtained by irradiation of bis-
(diazo) compound 4-2N2 in 2-methyltetrahydrofuran at 77 K
3 exp(-2J /kT)
1 + 3 exp(-2J /kT)
C
T
(ν0 ) 9.2152 GHz). (b-f) The same spectra observed at 5 (b),
80 (c), 90 (d), 120 (e), and 140 (f) K. (g) Simulated spectra of
34 with S ) 1, g ) 2.003, |D/hc| ) 0.0130 cm-1, |E/hc| ) 0.00
cm-1, and ∆B ) 25 G. (h) Simulated spectra of 34 with S ) 1,
g ) 2.003, |D/hc| ) 0.0115 cm-1, |E/hc| ) 0.00 cm-1, and ∆B )
17 G.
I )
(1)
where I is the intensity of the ESR active triplet state
and T, k, and C are the absolute temperature, Boltzman
constant, and an arbitrary constant, respectively. Fitting
the observed intensity data for thermally populated
triplets to eq 1 in the temperature range 6-75 K, where
the biscarbenes were chemically intact, gave an exchange
integral (J /k) value of -65 K (∆ET-S ) 266 cal/mol).
A similar irradiation of the bis(diazo) compound (4-
2N2) connected by a thiophene ring in 2-MTHF at 77 K
gave ESR spectra consisting of rather sharp and strong
signals at 320 and 340 mT (Figure 4a), along with weak
signals attributable to a monocarbene presumably formed
by incomplete decomposition of 4-2N2. The main signals
are reproduced well by computer simulation,15,16 as shown
in Figure 4g, employing a triplet Hamiltonian with S )
Therefore, we assigned the new, fine-structured peaks
3
to a quinoidal diradical triplet state of bis(carbene), 4.
Cooling the sample to 5 K resulted in a marked decrease
of the signal (Figure 4b), but the signal was regained
when the matrix was warmed. The intensity of the
signals increased rather monotonically up to 80 K. The
signals become sharp (|D/hc| ) 0.0115 cm-1, |E/hc| ≈ 0
cm-1) at around 90 K (Figure 4d), presumably because
of geometrical changes accompanied by softening of the
matrix.14 The intensity continued to increase up to 100
K but started to decrease above this temperature, and it
irreversibly disappeared completely at 140 K (Figure 4f).
The plot of intensity of the signal at 340 mT versus the
temperature from 4.3 to 70 K, where the shape of the
signals is unchanged, deviated from the Curie-Weiss law
1, g ) 2.003, |D/hc| ) 0.013 cm-1, and |E/hc| ≈ 0 cm-1
.
(17) Bleaney, B.; Bowers, K. D. Proc. R. Soc. London 1982, A214,
451.
J . Org. Chem, Vol. 69, No. 18, 2004 5873

Itoh et al.
F IGURE 6. UV-vis spectra obtained by irradiation of bis-
(diazo) compound 3-2N2. (a) Spectra of 3-2N2 in 2-methyl-
F IGURE 5. UV-vis spectra obtained by irradiation of mono-
diazo compound 2-N2. (a) Spectra of 2-N2 in 2-methyltetra-
hydrofuran at 77 K. (b) Sample from part a after irradiation
(λ > 350 nm). (c-e) Sample from parts a,b after thawing to
120 (c), 220 (d), and 270 (e) K.
tetrahydrofuran at 77 K. (b) Sample from part
a after
irradiation (λ > 350 nm). (c-d) Sample from parts a,b after
thawing to 95 (c) and 300 (d) K.
(Figure 3b), again confirming that the diradical was a
singlet ground state having a low-lying excited triplet
state. A nonlinear least-squares curve fitting the data
in Figure 3b to eq 1 yields the J / k value of -42 K (∆ET-S
) 167 cal/mol).
UV-Vis Sp ectr oscop ic Stu d y in a Ma tr ix a t Low
Tem p er a tu r e. Irradiation of 2-N2 in a 2-MTHF matrix
at 77 K resulted in rapid disappearance of the original
absorption due to 2-N2 and concurrent growth of sharp
and strong absorption bands at 322, 328, 361, 414, and
438 nm with weak broad bands extending to ca. 700 nm.
Similar absorption bands have been observed for a series
of triplet anthrylcarbenes7 and anthryl radicals.18 More-
over, because ESR signals ascribable to triplet carbene
32 are observed under identical conditions, the absorption
spectrum can be safely assigned to 32. When the matrix
was gradually warmed, the bands became sharper and
slightly shifted to a shorter wavelength to 320, 328, 359,
411, and 435 nm. These changes are often observed for
sterically congested triplet diarylcarbenes and are at-
tributable to geometrical changes of the species as the
matrix softens.14 Upon further warming, the band started
to disappear at ∼125 K and completely vanished at ∼270
K (Figure 5e).
Similar irradiation of 3-2N2 in a 2-MTHF matrix at
77 K resulted in rapid disappearance of the original
absorption due to 3-2N2 and concurrent growth of sharp
and strong absorption bands at 600 nm along with sharp
but weak bands at 362, 442, and 543 nm (Figure 6b),
which are completely different from those observed in the
photolysis of 2-N2. The matrix took on a distinct green
color. Because ESR signals attributable to a triplet state
of bis(carbene) 33 are observed under identical conditions,
the bands were assigned to 33. The bands were found to
be quite stable thermally. Thus, when the matrix was
gradually warmed, the bands became sharper and shifted
slightly to 362, 543, and 595 nm at around 95 K (Figure
6c). This is presumably related to the geometrical changes
F IGURE 7. UV-vis spectra obtained by irradiation of bis-
(diazo) compound 4-2N2. (a) Spectra of 4-2N2 in 2-methyl-
tetrahydrofuran at 77 K. (b) Sample from part
a after
irradiation (λ > 350 nm). (c-d) Sample from parts a,b after
thawing to 95 (c) and 300 (d) K.
associated with softening of the matrix.14 Upon further
warming, the band started to disappear at around 150
K but did not completely disappear until 300 K (Figure
6d). The anomalous thermal stability of 33 is noted here.
Similar irradiation of the bis(diazo) compound (4-2N2)
in 2-MTHF at 77 K gave a species showing a sharp
and strong band at 617 nm along with weak broad
bands at 365, 441, and 565 nm (Figure 7b). Because ESR
signals attributable to the triplet state of bis(carbene) 34
are observed under identical conditions, the bands are
3
assigned to 4. The bands were found to be quite stable
thermally as well. Upon warming of the matrix, the band
shifted slightly to 363, 446, 556, and 607 nm at around
95 K and started to disappear at 100 K, but it did not
disappear completely even at 300 K (Figure 7c,d).
UV-vis spectral observations indicate that the absorp-
tion bands observed for bis(carbene) are completely
different from those observed for the corresponding
(18) Adam, W.; Schneider, K.; Stapper, M.; Steeken, S. J . Am. Chem.
Soc. 1997, 119, 3280.
5874 J . Org. Chem., Vol. 69, No. 18, 2004

Preparation of Bis(diazo) Compounds
reagents, which is found to be of the first order (k ) 0.13
3
s-1). The lifetime of 2 is thus estimated to be 7.7 s.
Support is lent to this assignment by trapping experi-
ments using oxygen. The LFP of 2-N2 in a nondegassed
benzene solution at room temperature with a pulse from
a XeCl excimer laser produced a transient species show-
ing a broad absorption band with a maximum at 480 nm
that appeared at the expense of the absorption due to
32. The half-life of 32 decreased dramatically. The spent
solution was found to contain the corresponding ketone
(2-O) as the main product. It has been well docu-
mented21,22 that diarylcarbenes with triplet ground states
are readily trapped by oxygen to generate the corre-
sponding diaryl ketone oxides, which are easily and
directly observed by either matrix isolation or flash
photolysis and show a broad absorption band centered
at 390-450 nm. Thus, the observations can be inter-
preted to indicate that 32 is trapped by oxygen to form
carbonyl oxide (2-O2), which confirms the fact that the
F IGURE 8. Absorption of transient products formed during
irradiation of monodiazo compound 2-N2 in degassed benzene
at room temperature, recorded (a) 5, (b) 10, and (c) 30 s after
excitation. Inset shows the time course of the absorption at
433 nm (oscillogram trace).
3
transient absorption quenched by oxygen is due to 2.
The apparent built-up rate constant, kobs, of the car-
bonyl oxide (2-O2) is essentially identical to that of the
monocarbene. The strong absorption bands in the visible
regions that were observed for bis(carbene) systems
indicate the presence of an extended π-system19 and
support the idea that bis(carbene) is likely to exist as a
fully delocalized quinoidal form rather than a localized
one.
3
decay of 2, and kobs is expressed as given in eq 2
kobs ) k0 + kO [O2]
(2)
2
where k0 represents the rate of decay of 32 in the absence
of oxygen and kO is the quenching rate constant of 32 by
2
It is interesting that the bands ascribable to a mono-
carbene, whose generation was expected by elimination
of one diazo group, were not appreciably detected even
at the initial stage of the irradiation, suggesting that the
simultaneous elimination of two nitrogen molecules is
likely to be a major process under these conditions.20
Tim e-R esolved UV-Vis Sp ect r oscop ic St u d y in
Solu tion a t Room Tem p er a tu r e. To determine the
stability of the present carbenes more accurately, the
lifetime is estimated in degassed benzene at room tem-
perature, in which we measured the lifetime of a series
of sterically congested diarylcarbenes.8
Laser flash photolysis (LFP) of 2-N2 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 absorption bands with a
maximum at 320, 359, and 433 nm (Figure 8). The UV-
vis spectrum obtained just after irradiation of 2-N2 in
degassed benzene at 20 °C is essentially the same as that
observed in the photolysis in 2-MTHF at 77 K and, hence,
is attributable to 32. The absorption bands decayed very
slowly; the transient bands did not disappear completely
even after 1 min under these conditions. The inset in
Figure 8 shows the decay of 32 in the absence of trapping
oxygen. A plot of the observed pseudo-first-order rate
constant of the formation of the oxide against [O2] is
linear (Supporting Information Figure S1). From the
slope of this plot, kO was determined to be 7.6 × 106 M-1
2
s-1, which is approximately 3 orders of magnitude smaller
than that observed with the parent triplet diphenylcar-
bene (kO ) 5.0 × 109 M-1 s-1).22
2
On the other hand, the transient absorption bands
observed in the photolysis of bis(diazo) compounds are
significantly more stable than those of the corresponding
monocarbene. The lifetime of the transient species gener-
ated in the photolysis of bis(diazo) compounds was too
long to monitor with a laser flash photolysis technique,
and in this case, it was more convenient to use the
conventional UV-vis spectroscopic method. The photoly-
sis of 3-2N2 in degassed benzene gave a transient
product showing a strong absorption band at 595 nm
along with weak bands at 361 and 430 nm (Figure 9).
The spectra are very similar to those observed in the
photolysis of 3-2N2 in 2-MTHF at 77 K and, hence, are
assigned to 33. The transient bands decayed very slowly.
It took more than 2 h for all of the bands to disappear
completely. The decay curve was best analyzed by second-
order kinetics with 2k/ꢀl ) 0.024 min-1, t1/2 ) 20 min.
Although those transient bands are fairly stable, the
decay rate was dramatically accelerated by the presence
of oxygen, and the analysis of the spent solution showed
the presence of the corresponding diketones (3-2O),
indicating that they are also quenched by oxygen. Be-
cause of the strong absorption band of 33, the bands that
are ascribable to the corresponding oxides could not be
detected. However, the plot of the decay of 33 against [O2]
(19) (a) Harder, T.; Bendig, J .; Scholz, G.; Sto¨sser, R. J . Am. Chem.
Soc. 1996, 118, 2497. (b) Harder, T.; Sto¨ber, R.; Wessig, P.; Bendig, J .
J . Photochem. Photobiol., A 1997, 103, 105. (c) Tomioka, H.; Sawai, S.
Org. Biomol. Chem. 2003, 1, 4441. (d) Serwinski, P. R.; Lahti, P. M.
Org. Lett. 2003, 5, 2099.
(20) It is to be noted here that, in the photolysis of poly(diazo)
compounds in 2-MTHF matrix at low temperatures, photo-deazetation
processes are sensitive to experimental conditions, such as wavelength
and intensity of the light and concentration of the precursor. See: (a)
Teki, Y.; Takui, T.; Yagi, H.; Katoh, K.; Iwamura, H. J . Chem. Phys.
1985, 83, 539. (b) Matsuda, K.; Nakamura, N.; Inoue, K.; Koga, N.;
Iwamura, H. Bull. Chem. Soc. J pn. 1996, 69, 1483. (c) Nakamura, N.;
Inoue, K.; Iwamura, H. Angew. Chem., Int. Ed. Engl. 1993, 32, 872.
(d) Sugawara, T.; Inada, M.; Iwamura, H. Tetrahedron Lett. 1983, 24,
1723.
(21) See for review: (a) Sander, W. Angew. Chem., Int. Ed. Engl.
1990, 29, 344. (b) Bunnelle, W. Chem. Rev. 1991, 91, 336.
(22) Scaiano, J . C.; McGimpsey, W. G.; Casal, H. L. J . Org. Chem.
1989, 54, 1612.
J . Org. Chem, Vol. 69, No. 18, 2004 5875

Itoh et al.
interaction between the triplet centers is topologically
prohibited, but communication via shared π-space is
possible, thereby generating high-spin states. Consider-
ably less is known about their conjugated cousins,
p-phenylene systems, where spin pairing between the
triplet carbene units leads to lower-spin states.23
For instance, p-phenylenebis(methylene) is predicted
to have a singlet ground state of A′ symmetry with a
delocalized diradical structure.25 The lower-lying excited
state is computed to be the 3A′ state about 2 kcal/mol
5
higher in energy, and the A′ quintet state lies about 27
kcal/mol above the 1A′ state. Although the 3A′ triplet state
was not detected by ESR even at low temperature,
probably because of its high reactivity, the species has
been generated in an inert gas matrix at 10 K and
characterized by a trapping reaction with O2 and HCl
under these conditions.25 The triplet state of p-phenylene-
bis(phenylmethylene) is detected by ESR and is shown
to be a thermally populated state lying about 1 kcal/mol
above the ground-state singlet diradical.26
F IGURE 9. Absorption of transient products formed during
irradiation of bis(diazo) compound 3-2N2 in degassed benzene
at room temperature, recorded (a) before irradiation, (b)
immediately after irradiation, and (c) 300 min after excitation.
Inset shows the time course of the absorption at 588 nm.
A series of p-phenylenebis(diradicals), in which the
local diradical centers are changed from phenylnitrene,
having a triplet ground state with a σπ singlet lying 18
kcal/mol higher in energy, to phenylchlorocarbene, having
a σ2 singlet ground state with a triplet lying 7-9 kcal/
mol higher in energy, has been generated in an inert gas
matrix at low temperature and characterized by IR in
combination with theoretical calculations.23,27 These stud-
1
ies reveal that all of the systems have A′ singlet ground
3
5
states, with A′ and A′ about 2 and 29 kcal/mol higher
in energy, respectively, indicating that the relative ener-
1
gies among the three A′ states change very little regard-
less of the nature of the local diradical subunits.
The effect of a coupling linker has been extensively
studied, not for the systems with bis(carbene) units28
but for those with bis(nitrene) units. For instance, two
nitrene centers introduced into a coupling linker group,
such as benzene,29 biphenyl,30 stilbene,31 diphenylbuta-
F IGURE 10. Absorption of transient products formed during
irradiation of bis(diazo) compound 4-2N2 in degassed benzene
at room temperature, recorded (a) immediately after excitation,
and 1 (b), 2 (c), 5 (d), 10 (e), and 15 (f) h after excitation. Inset
shows the time course of the absorption at 605 nm.
(23) See for review: (a) Zuev, P.; Sheridan, R. S. Tetrahedron 1995,
42, 1337. (b) Nicolaides, A.; Tomioka, H. In Photochemistry of Organic
Molecules in Isotropic and Anisotropic Media; Ramamurthy, V.,
Schanze, K. S., Eds.; Marcel Dekker: New York, 2003; pp 133-184.
(c) Nicolaides, A.; Tomioka, H. J . Photosci. 2003, 10, 165.
(24) Koga, N.; Iwamura, H. In Carbene Chemistry; Bertrand, G., Ed.;
FontisMedia: Lausanne, Switzerland, 2002; pp 271-296.
(25) Subhan, W.; Rempala, P.; Sheridan, R. S. J . Am. Chem. Soc.
1998, 120, 11528. See also: J ean, Y. J . THEOCHEM 1998, 424, 29.
(26) (a) Trozollo, A. M.; Murray, R. W.; Smolinsky, G.; Yager, W.
A.; Wasserman, E. J . Am. Chem. Soc. 1963, 85, 2526. (b) Sixl, H.;
Mathes, R.; Schapp, A.; Ulrich, K.; Huber, R. Chem. Phys. 1986, 107,
105. (c) Itoh, K. Pure Appl. Chem. 1978, 50, 1251.
(27) (a) Tukada, H.; Mutai, K.; Iwamura, H. J . Chem. Soc., Chem.
Commun. 1987, 1159. (b) Zuev, P. S.; Sheridan, R. S. J . Am. Chem.
Soc. 1993, 115, 3788. (c) Tomioka, H.; Komatsu, K.; Nakayama, T.;
Shimizu, M. Chem. Lett. 1993, 1291. (d) Zuev, P. S.; Sheridan, R. S. J .
Org. Chem. 1994, 59, 2267. (e) Zuev, P. S.; Sheridan, R. S. J . Am. Chem.
Soc. 1994, 116, 9381. (f) Nicolaides, A.; Tomioka, H.; Murata, S. J .
Am. Chem. Soc. 1998, 120, 11530. (g) Nicolaides, A.; Enyo, T.; Miura,
D.; Tomioka, H. J . Am. Chem. Soc. 2001, 123, 2629.
is linear (Supporting Information Figure S2), and from
the slope, the quenching rate constant (kO ) for 33 was
2
determined to be 7.6 × 104 M-1 s-1
.
Similar photolysis of 4-2N2 also generated transient
3
bands ascribable to 4, again, by comparison with those
observed in the photolysis in 2-MTHF at 77 K. The
3
transient bands due to 4 decayed even more slowly; it
took more than 10 h for all of the bands to disappear
completely (Figure 10). The decay curve was analyzed
as a combination of second-order (2k/ꢀl ) 5.5 × 10-3
min-1, t1/2 ) 3.5 h) and first-order kinetics (k ) 3.9 × 10-3
min-1, τ ) 4.2 h). The decay rate was again dramatically
accelerated by the presence of oxygen. The quenching
(28) The role of bridging heteroatoms such as oxygen, sulfur,
sulfoxide, sulfone, and thisxanthene in effecting the magnetic coupling
between two triplet phenylcarbene centers has been investigated.
See: Matsuda, K.; Yamagata, T.; Seta, T.; Iwamura, H.; Hori, K. J .
Am. Chem. Soc. 1997, 119, 8057 and ref 15.
3
rate constant (kO ) for 4 was determined to be 4.0 × 104
2
M-1 s-1 (Supporting Information Figure S3).
(29) Singh, A.; Brinen, J . S. J . Am. Chem. Soc. 1971, 93, 540.
(30) (a) Ling, C.; Lahti, P. M. Chem. Lett. 1993, 769. (b) Ohana, T.;
Kaise, M.; Nimura, S.; Kikuchi, O.; Yabe, A. Chem. Lett. 1993, 765.
(c) Ohana, T.; Kaise, M.; Yabe, A. Chem. Lett. 1992, 1397. (d) Ohana,
T.; Ouchi, A.; Moriyama, H.; Yabe, A. J . Photochem. Photobiol., A 1993,
72, 83. (g) Minato, M.; Lahti, P. M.; van Willigen, H. J . Am. Chem.
Soc. 1993, 115, 4532.
Discu ssion
Numerous studies have been done to construct high-
spin systems built around triplet carbene subunits linked
across m-phenylene.11b,23,24 In these systems, covalent
5876 J . Org. Chem., Vol. 69, No. 18, 2004

Preparation of Bis(diazo) Compounds
SCHEME 4
diene,31a,b diphenyloctatetraene,31a,b diphenylacetylene,32
diphenylbutadiyne,32 tetraphenylallene,33 benzophenone,34
1,1-diphenylethylene,34 diphenyl sulfide,35 azobenzene,35
and thiophene,36 have all been generated in a conjugative
manner and characterized by ESR, which revealed that
all have a singlet ground state with a delocalized diradi-
cal structure having a very small singlet-triplet energy
gap of 150-600 cal/mol.
The present findings, showing that two persistent
diarylcarbene units introduced on either thiophene or
butadiyne systems have a singlet quinoidal biradical
ground state with a very small singlet-triplet energy
gap, are in full accordance with previous observations and
predictions.
of unpaired electrons throughout the π-net framework.
This is further supported by the observation that 1,3-
bis[3,5-dimethyl-4-(anthrylcarbeneno)phenyl]benzene, a
high-spin analogue of the present system, has essentially
identical stability to that of the corresponding monocar-
bene.37
Despite the stability, both bis(carbenes), 3 and 4,
are readily trapped by oxygen, although the quench-
ing rate constants observed for 3 and 4 are 2 orders
of magnitude smaller than those of the isolated local
carbene unit 2.
Con clu sion
The present investigation revealed that sterically
congested diphenyldiazomethanes can be used as build-
ing blocks to prepare functionalized bis(diazo) com-
pounds. Fairly stable bis(carbenes) with fully delocalized
diradical structures are realized by this method, which
enabled us to study the reactivity of those molecules for
the first time. Although these molecules are not candi-
dates for practical use in the development of organo-
ferromagnetic materials, they are of considerable impor-
tance in understanding the nature of open-shell organic
molecules. The present method can easily be extended
to construction of precursor poly(diazo) compounds, which
can generate high-spin polycarbenes with considerable
stability.
Most studies on those species have been done simply
by using ESR because the measurements have been
crucial for characterization of those paramagnetic species
and have been successfully employed in many systems.
However, almost no information is available on the
electronic properties and reactivities of those interesting
species. In the present study, we have measured UV-
vis spectra and have also revealed their reactivity in
solution at room temperature.
Both bis(carbenes), 3 and 4, are characterized by very
sharp and strong absorption bands in the visible region.
These features are usually noted for some diradical
species incorporated into quinoidal cumulated π-conju-
gating systems (Scheme 4).19 These observations provide
further evidence for the contribution of a fully delocalized
diradical structure. The surprising thermal stability of
the absorption bands is noted. Thus, the bands due to 4
survive even at room temperature. In accordance with
this, 4 survives for hours in solution at room temperature
and is stable enough to be observable by the conventional
spectroscopic means. A remarkable increase in the
lifetime of biscarbenes 3 and 4, as opposed to the isolated
local diradical system, suggests that the biscarbenes are
thermodynamically stabilized as a result of delocalization
Exp er im en ta l Section
9-(4-t-Bu tyl-2,6-dim eth ylph en yl)an th r acen e. To a stirred
solution of 4-t-butyl-2,6-dimethylbromobenzene38 (5.0 g, 20.7
mmol) in dry ether (40 mL) was added dropwise a 1.50 M
n-pentane solution of t-butyllithium (30.4 mL, 45.6 mmol) at
-78 °C under an argon atmosphere. After stirring for 1 h, the
mixture was allowed to warm to room temperature. A solution
of anthrone39 (4.0 g, 20.7 mmol) in dry toluene (80 mL) was
added dropwise to the mixture, and the mixture was refluxed
overnight. After cooling to room temperature and adding
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, n-hexane)
followed by short-path distillation (68° C/0.1 Torr) to give 9-(4-
t-butyl-2,6-dimethylphenyl)anthracene (3.1 g, 44%) as a pale
(31) (a) Minato, M.; Lahti, P. M. J . Phys. Org. Chem. 1993, 6, 483.
(b) Minato, M.; Lahti, P. M. J . Am. Chem. Soc. 1997, 119, 2187. (c)
Mimura, S.; Kikuchi, O.; Ohana, T.; Yabe, A.; Kaise, M. Chem. Lett.
1996, 125.
(32) Murata, S.; Iwamura, H. J . Am. Chem. Soc. 1991, 113,
5547.
(33) Yamagata, T.; Tukada, H.; Kobayashi, K. Chem. Lett. 1998,
129.
(34) Ling, C.; Minato, M.; Lahti, P. M.; van Willigen, H. J . Am.
Chem. Soc. 1992, 114, 9959.
(35) Mimura, S.; Kikuchi, O.; Ohana, T.; Yabe, A.; Kaise, M. Chem.
Lett. 1994, 1679.
(36) Itoh, T.; Hirai, K.; Tomioka, H. J . Am. Chem. Soc. 2004, 126,
1130-1140.
(37) Ling, A.; Lahti, P. M. J . Am. Chem. Soc. 1994, 116, 8784.
(38) Prisinzano, T.; Law, H.; Dukat, M.; Slassi, A.; MaClean, N.;
Demchyshyn, L.; Glennon, R. A. Bioorg. Med. Chem. 2001, 9, 613.
(39) Organic Syntheses; Wiley & Sons: New York, 1956; Collect. Vol.
I, p 60.
J . Org. Chem, Vol. 69, No. 18, 2004 5877

Itoh et al.
1
yellow solid. Mp 167° C. H NMR (300 MHz, CDCl3, ppm): δ
ture of ethyl carbamate (4.6 g, 51.6 mmol) and silver tetrafluoro-
borate (0.6 g, 2.8 mmol) was heated to 60 °C. A solution of
chloromethane (1.5 g, 2.6 mmol) in dry dioxane (13 mL)
was added dropwise to this mixture at the same temperature.
After refluxing overnight, the reaction mixture was filtered;
the filtrate was then 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 purified by column
chromatography (silica gel, hexane/dichloromethane ) 1:1)
to give ethyl N-[9-{10-(4-t-butyl-2,6-dimethyl)phenyl}anthryl]-
(4-bromo-2,6-dimethylphenyl)methylcarbamate (1.2 g, 75%)
as a pale brown solid. Mp 136.6-137.2 °C. 1H NMR (300 MHz,
∼8.47-7.29 (m, 9H, 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. EIMS (m/z): 338 (base,
M+), 323 (41.3, M+ - Me). HRMS calcd for C26H26, 338.2035;
found (m/z), 338.2034.
9-(4-t-Bu tyl-2,6-d im eth ylp h en yl)-10-br om oa n th r a cen e.
Bromine (0.5 mL, 9.0 mmol) was added to a stirred solution
of phenylanthracene (3.1 g, 9.0 mmol) in carbon tetrachloride
(40 mL) at 0 °C. The solution was stirred at room temperature
overnight. The reaction 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 n-hexane to
give 9-(4-t-butyl-2,6-dimethylphenyl)-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. EIMS
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 (t, 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.
MS m/z (relative intensity): 623 (M + 2, 100), 621 (M+, 94.7),
364 (29.2), 339 (30.3), 283 (30.9), 212 (87.4), 210 (86.2), 57
(42.9). HRMS calcd for C38H40BrNO2, 621.2242; found (m/z),
621.2196.
(m/z): 418 (base, M + 2), 416 (98.0, M + 1), 401 (32.3, M+
-
Me). HRMS calcd for C26H25, 416.1139; found (m/z), 416.1125.
[9-{10-(4-t-Bu tyl-2,6-dim eth yl)ph en yl}an th r yl](4-br om o-
2,6-d im eth ylp h en yl)m eth a n ol. A 2.66 M hexane solution
of n-butyllithium (2.2 mL, 5.8 mmol) under an argon atmo-
sphere was added dropwise to a stirred solution of bromo-
anthracene (2.0 g, 4.8 mmol) in dry ether (40 mL) at 0 °C. After
the mixture stirred for 3 h, a solution of 4-bromo-2,6-dimeth-
ylbenzaldehyde40 (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 the 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 concen-
trated 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-t-butyl-2,6-dimethyl)-
phenyl}anthryl](4-bromo-2,6-dimethylphenyl)methanol (2.0 g,
74%) as a yellow solid. Mp 99.5-100.0 °C. 1H NMR (300 MHz,
CDCl3, ppm): δ ∼8.49-7.25 (m, 8H, Anth-H), 7.48 (d, J )
4.04 Hz, 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. EIMS m/z (relative
intensity): 552 (M + 2, 39.5), 550 (M+, 40.1), 339 (100), 283
E t h yl
N-Nit r oso-N-[9-{10-(4-t-b u t yl-2,6-d im et h yl)-
p h en yl}a n t h r yl](4-b r om o-2,6-d im et h ylp h en yl)m et h yl-
ca r ba m a te. Nitrogen dioxide (5.0 g) was bubbled into dry
carbon tetrachloride (20 mL) at -20 °C while stirring. Sodium
acetic acid (9.0 g, 0.10 mol) 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 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-t-butyl-2,6-dimethyl)phenyl}anthryl]-
(4-bromo-2,6-dimethylphenyl)methylcarbamate (1.4 g, quan-
1
titative) as a yellow solid. H 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 (t, 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.
[9-{10-(4-t-Bu tyl-2,6-dim eth yl)ph en yl}an th r yl](4-br om o-
2,6-d im eth ylp h en yl)d ia zom eth a n e (1-N2). Potassium t-
butoxide (0.5 g, 4.7 mmol) at -20 °C under an argon atmo-
sphere was added to a stirred solution of the nitroso-carbamate
(1.4 g, 2.2 mmol) in dry tetrahydrofuran (15 mL). After stirring
overnight, the reaction mixture was poured into ice and
extracted with ether. 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, n-hexane
at -20 °C), followed by GPC (chloroform, monitored at 350
nm) to give 1-N2 (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,
(40.9), 213 (69.8), 211 (71.8), 57 (68.4). HRMS calcd for C35H35
BrO, 550.1871; found (m/z), 550.1862.
-
[9-{10-(4-t-Bu tyl-2,6-dim eth yl)ph en yl}an th r yl](4-br om o-
2,6-d im eth ylp h en yl)ch lor om eth a n e. Gaseous hydrochloric
acid, prepared by adding hydrochloric acid (10 mL) to concen-
trated sulfuric acid (15 mL), was bubbled into a stirred solution
of the methanol (1.5 g, 2.7 mmol) in dry benzene (20 mL) for
1 h at 5 °C while monitoring the reaction by 1H NMR. The
reaction mixture was concentrated and dried under reduced
pressure to give [9-{10-(4-t-butyl-2,6-dimethyl)phenyl}anthryl]-
(4-bromo-2,6-dimethylphenyl)chloromethane (1.5 g, 97%) as a
1
yellow solid. H 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.
122.7, 120.8, 57.1, 34.5, 31.5, 21.1, 20.3. IR (KBr, cm-1): νCdN
2041.
2
[9-{10-(4-t-Bu tyl-2,6-d im eth yl)p h en yl}a n th r yl](2,6-d i-
m eth yl-4-tr im eth ylsilyleth yn ylph en yl)diazom eth an e (2-
N2). To a stirred mixture of 1-N2 (135.0 mg, 0.24 mmol),
bis(triphenylphosphino)palladium dichloride (catalytic amount),
and copper iodide (catalytic amount) in dry triethylamine
(4 mL) and dry tetrahydrofuran (2 mL) was added trimethyl-
Eth yl N-[9-{10-(4-t-Bu tyl-2,6-d im eth yl)p h en yl}a n th r yl]-
(4-br om o-2,6-d im eth ylp h en yl)m eth ylca r ba m a te. A mix-
(40) Yamakawa, M.; Kubota, T.; Akazawa, H. Bull. Chem. Soc. J pn.
1967, 40, 1600.
5878 J . Org. Chem., Vol. 69, No. 18, 2004

Preparation of Bis(diazo) Compounds
silylacetylene (100.0 µL, 0.72 mmol) under nitrogen atmo-
sphere. After heating overnight at 35 °C, the reaction mixture
was concentrated under reduced pressure, and the residue was
dissolved in ether and filtered. The filtrate was then concen-
trated and dried under reduced pressure to leave a crude
product, which was purified by GPC (chloroform, monitored
at 350 nm) to afford 2-N2 (2.0 g, 74%) as an orange, viscous
liquid. 1H NMR (300 MHz, CDCl3, ppm): δ ∼8.00-7.28 (m,
10H, Anth-H + Anth-Ph-H), 7.26 (s, 2H, Ph-H), 2.11 (s,
6H, Ph-Me), 1.73 (s, 6H, Anth-Ph-Me), 1.44 (s, 9H, -tBu),
0.25 (s, 9H, -TMS). 13C NMR (75.5 MHz, CDCl3, ppm):
δ 150.5, 138.1, 136.80, 136.78, 134.3, 132.8, 131.4, 130.3,
130.1, 127.2, 126.3, 125.4, 125.2, 124.5, 123.0, 121.6, 105.1,
isolated by preparative TLC and identified by NMR and MS.
The following products were isolated and charatcterized.
Bu ta d iyn e-d ik eton e (3-2O). 1H NMR (300 MHz, CDCl3,
ppm): δ 8.05 (d, J ) 9.00 Hz, 4H), 7.51 (d, J ) 8.64 Hz, 4H),
7.44-7.39 (m, 4H), 7.32-7.30 (m, 4H), 7.30 (s, 4H), 7.21 (s,
4H), 2.13 (s, 12H), 1.73 (s, 12H), 1.44 (s, 18H). MS (MALDI-
TOF) calcd for C74H65O2 (M - H+), 985.4979; found (m/z),
985.5131.
Th iop h en e-d ik eton e (4-2O). 1H NMR (300 MHz, CDCl3,
ppm): δ 8.10 (d, J ) 8.82 Hz, 4H), 7.51 (d, J ) 8.23 Hz, 4H),
7.44-7.21 (m, 18H), 2.20 (s, 12H), 1.74 (s, 12H), 1.45 (s, 18H).
MS (MALDI-TOF) calcd for C74H67O2S (M - H+), 1019.4856;
found (m/z), 1019.4973.
EP R Mea su r em en ts. The diazo compound was dissolved
in 2-methyltetrahydrofuran (10-3 M), and the solution was
degassed in a quartz cell by 3 freeze-degas-thaw cycles. The
sample was cooled in an optical transmission EPR cavity at
77 K and irradiated with a 500 W Xe or Hg lamp using a Pyrex
filter. EPR spectra were measured on an ESR spectrometer
(X-band microwave unit, 100 kHz field modulation). The signal
positions were read by the use of a gaussmeter. The temper-
ature was controlled by a digital temperature indicator/
controller, which provided accuracy of the measurements
within (0.1 K and the control ability within (0.2 K. Errors
in the measurements of component amplitudes did not exceed
5%, and the accuracy of the resonance field determination was
within (0.5 mT.
Low -Tem p er a t u r e UV-Vis Sp ect r a . Low-temperature
spectra at 77 K were obtained by using a variable-temperature
liquid-nitrogen cryostat 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 300 W high-
pressure mercury lamp using a Pyrex filter, and the spectral
changes were recorded at appropriate time intervals. The
spectral changes upon thawing were also monitored by care-
fully controlling the matrix temperature with a temperature
controller.
F la sh P h otolysis. All of the flash measurements were
made on a 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 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 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.
A 150 W xenon short arc lamp (L 2195) was used as the
probe source, and the monitoring beam, guided with an optical
fiber scope, was arranged in an orientation perpendicular to
the excitation source. The probe beam was monitored with a
photomultiplier tube through a linear image sensor (512
photodiodes used). The timing of the excitation pulse, the probe
beam, and the detection system was achieved through a digital
synchroscope interfaced to a computer. This allowed for rapid
processing and storage of the data and provided printed
graphic capabilities. Each trace was also displayed on a
monitor.
A sample was placed in a long-necked Pyrex tube with a
sidearm connected to a quartz fluorescence cuvette and de-
gassed using a minimum of 4 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
94.5, 57.8, 34.5, 31.5, 21.1, 20.3, -0.01. IR (NaCl, cm-1): νCdN
2
2040, νCtC 2153.
1,4-Bis(3,5-d im et h yl-4-[9-{10-(4-t-b u t yl-2,6-d im et h yl)-
p h en yl}a n th r yl]d ia zom eth ylp h en yl)bu ta d iyn e (3-2N2).
To a solution of 2-N2 (16.8 mg, 0.03 mmol) in t-butyl alcohol
(1 mL) was added 10% aqueous sodium hydroxide (0.3 mL).
After stirring overnight at room temperature, the reaction
mixture was 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 GPC (chloroform,
monitored at 350 nm) to afford a deprotected diazo compound
(11.7 mg, 80%) as an orange, viscous liquid. 1H NMR (300
MHz, CDCl3, ppm): δ ∼8.00-7.29 (m, 8H, Anth-H), 7.27 (s,
2H, Ph-H), 7.25 (s, 2H, Anth-Ph-H), 3.09 (s, 1H, acetylene),
2.13 (s, 6H, Ph-Me), 1.74 (s, 6H, Anth-Ph-Me), 1.44 (s, 9H,
-tBu). IR (NaCl, cm-1): νCdN 2041.
2
To a solution of the deprotected diazo compound (10.6 mg,
0.02 mmol) in dichloromethane (2 mL) was added CuCl(OH)‚
TMEDA (catalytic amount) under an oxygen atmosphere. After
stirring overnight at room temperature, the reaction mixture
was filtered, 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 give 3-2N2 (6.0
mg, 57%) as an orange, viscous liquid. 1H NMR (300 MHz,
CDCl3, ppm): δ ∼8.00-7.29 (m, 8H, Anth-H), 7.27 (s, 2H,
Ph-H), 7.25 (s, 2H, Anth-Ph-H), 3.09 (s, 1H, acetylene), 2.13
(s, 6H, Ph-Me), 1.74 (s, 6H, Anth-Ph-Me), 1.44 (s, 9H, -tBu).
13C NMR (75.5 MHz, CDCl3, ppm): δ 150.6, 138.3, 136.9, 136.8,
134.3, 133.2, 132.3, 130.3, 130.1, 127.2, 126.5, 125.5, 125.1,
124.5, 122.8, 120.2, 81.9, 74.4, 57.9, 34.5, 31.5, 21.1, 20.3. IR
(NaCl, cm-1): νCdN 2041, νCtC 2153.
2
2,5-Bis(3,5-d im et h yl-4-[9-{10-(4-t-b u t yl-2,6-d im et h yl)-
p h en yl}a n th r yl]d ia zom eth ylp h en yl)th iop h en e (4-2N2).
Palladium acetate (0.8 mg, 3.6 × 10-3 mmol), potassium
fluoride (6.2 mg, 0.11 mmol), 2-(di-t-butylphosphino)biphenyl
(3.2 mg, 1.1 × 10-2 mmol), and 2.5-thiophene diboronic acid
(3.1 mg, 0.02 mmol) were added to a stirred solution of 1-N2
(20.0 mg, 0.04 mmol) in dry tetrahydrofuran (0.5 mL) under a
nitrogen atmosphere. After heating overnight at 35 °C, the
reaction mixture was filtered, 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)
1
to afford 4-2N2 (1.6 mg, 8%) as an orange, viscous liquid. H
NMR (300 MHz, CDCl3, ppm): δ ∼8.08-7.42 (m, 12H, Anth-
H), 7.42 (s, 2H, thiophene-H), ∼7.35-7.28 (m, 4H, Anth-H),
7.31 (s, 4H, Ph-H), 7.26 (s, 4H, Anth-Ph-H), 2.21 (s, 12H,
Ph-Me), 1.75 (s, 12H, Anth-Ph-Me), 1.44 (s, 18H, -tBu). 13
C
NMR (75.5 MHz, CDCl3, ppm): δ 150.5, 143.0, 138.0, 137.5,
136.8, 134.4, 133.0, 130.3, 130.1, 130.0, 127.2, 126.4, 126.3,
125.4, 125.3, 124.5, 123.9, 123.3, 57.6, 34.5, 31.5, 21.4, 20.3.
IR (NaCl, cm-1): νCdN 2039.
2
Ir r a d ia tion for P r od u ct An a lysis. In a typical run, a
solution of the diazo compound (1, ca. 5 mg) in solvent was
placed in a Pyrex tube and irradiated with a high-pressure,
300 W mercury lamp until all of the diazo compound was
destroyed. The irradiation mixture was then concentrated on
a rotary evaporator below 20 °C. Individual components were
J . Org. Chem, Vol. 69, No. 18, 2004 5879

Itoh et al.
concentration of the sample was adjusted in order to absorb a
significant portion of the excitation light. For experiments in
which the rate constant for the reaction of oxygen with
carbenes was determined, varying concentrations of oxygen
in nitrogen were bubbled through the solution.41
Specially Promoted Research (12002007). Support from
the Mitsubishi Foundation and the Nagase Science and
Technology Foundation is also appreciated.
Su p p or tin g In for m a tion Ava ila ble: Plot of the growth
rate of the carbonyl oxide from the photoproduct of 2-N2
(Figure S1), 3-2N2 (Figure S2), and 4-2N2 (Figure S3) as a
Ack n ow led gm en t. The authors are grateful to the
Ministry of Education, Culture, Sports, Science
and Technology of J apan for support of this work
through a Grant-in-Aid for Scientific Research for
1
function of oxygen concentration and H NMR spectra of 2-N2
(Figure S4), 3-2N2 (Figure S5), and 4-2N2 (Figure S6). This
material is available free of charge via the Internet at
http://pubs.acs.org.
(41) Scaiano, J . C.; McGimpsey, W. G.; Casal, H. L. J . Org. Chem.
1989, 54, 1612.
J O0494026
5880 J . Org. Chem., Vol. 69, No. 18, 2004