Quintet bis(carbene) from triplet diarylcarbenes introduced at the 1,8-position of anthracene

Article abstract of DOI:10.1021/ol049877j

[9-{10-Phenyl}anthryl](4-bromo-2,6-dimethylphenyl)diazomethane was found to be stable enough to survive Sonogashira coupling reaction conditions and was converted to [9-{10-phenyl}anthryl](4-trimethylsilylethynyl-2,6-dimethylphenyl) diazomethane, which wa

Full text of DOI:10.1021/ol049877j

ORGANIC
LETTERS
2004
Vol. 6, No. 5
847-850
Quintet Bis(carbene) from Triplet
Diarylcarbenes Introduced at the
1,8-Position of Anthracene
Yusuke Ohtsuka,† Tetsuji Itoh,† Katsuyuki Hirai,‡ Takeji Takui,§ and
,†
Hideo Tomioka*
Chemistry Department for Materials, Faculty of Engineering, Mie UniVersity,
Tsu, Mie 514-8507, Japan, Instrumental Analysis Facilities, Life Science Research
Center, Mie UniVersity, Tsu, Mie 514-8507, Japan, and Department of Chemistry and
Material Science, Faculty of Science, Osaka City UniVersity, Sumiyoshi-ku,
Osaka, 558-8585, Japan
tomioka@chem.mie-u.ac.jp
Received January 21, 2004
ABSTRACT
[9-{10-Phenyl}anthryl](4-bromo-2,6-dimethylphenyl)diazomethane was found to be stable enough to survive Sonogashira coupling reaction
conditions and was converted to [9-{10-phenyl}anthryl](4-trimethylsilylethynyl-2,6-dimethylphenyl)diazomethane, which was reacted with 1,8-
diiodoanthracene to give bis(diazo) compound. Bis(carbene) generated by irradiation of the bis(diazo) compound generated a fairly persistent
S ) 2 quintet state.
Recently, there has been much interest in the synthesis of
organic materials with magnetic properties for potential
organo-magnetic materials.1,2 In this regard, a great deal of
work has been directed toward high-spin polycarbenes, in
which the carbenic subunits are coupled in a ferromagnetic
fashion.3 The majority of the high-spin systems that have
been investigated focused on meta-phenylene linkers, as in
the prototypical m-phenylenebis(methylene).4 It is potentially
possible to use a polynuclear aromatic compound as a linker.
† Faculty of Engineering, Mie University.
‡ Life Science Research Center, Mie University.
§ Osaka City University.
(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.
Bulletin; Materials Research Society: Warrendale, PA, 2000; Vol. 25, p
21. (i) Miller, J. S., Drillon, M., Eds. Magnetism: Molecules to Materials
II; Wiley-VCH: Weinheim, 2001. (j) Itoh, K., Kinoshita, M., Eds. Molecular
Magnetism; Kodansha-Gordon and Breach: Tokyo, 2000.
(3) (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; American Chemical
Society: Washington, 1996; p 142. (c) Koga, N.; Iwamura, H. In Magnetic
Properties of Organic Materials; Lahti, P., Ed.; Marcel Dekker: New York,
1999; pp 629-659.
(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; 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., Eds. MRS
10.1021/ol049877j CCC: $27.50 © 2004 American Chemical Society
Published on Web 02/11/2004

For instance, radical centers properly introduced on an-
thracene rings interact ferromagnetically to generate a high-
spin state.5,6 Those polynuclear aromatic compounds have
an advantage over simple aromatic rings in that they have
more positions to accept spin sources. The maximum number
of available positions for ferromagnetic coupling in naph-
thalene and anthracene are four and five, respectively, while
this number is three for benzene. Thus, a spin state with a
spin-quantum number higher than three in one molecule can
be generated by using polynuclear aromatic rings. However,
almost no attempts have been made to introduce triplet
carbene units on a polynuclear aromatic system. This is most
probably because of the difficulty entailed in synthesizing a
proper precursor. The diazo functional groups are sensitive
not only to heat and light but also to acid, metal, and other
reagents employed for further modification and, hence, are
usually introduced at the last step of the synthesis.7 This
makes the versatility of the group less variable. In this paper,
we report the experimental results for triplet carbene spin
coupling through an anthracene unit.
Scheme 1
trimethylsilylacetylene in the presence of (Ph3P)2PdCl2 and
CuI at 40 °C for 2 days gave [9-{10-phenyl}anthryl](4-
trimethylsilylethynyl-2,6-dimethylphenyl)diazomethane (2-
N2-TMS). Deprotection12 of the trimethylsilyl group with
NaOH proceeded smoothly to give an ethynyl derivative (2-
N2). A desired bis(diazo) compound (3-2N2) was relatively
easily prepared in 45% yield by coupling 2 equiv of 2-N2
with 1,8-diiodoanthracene13 under mild Sonogashira coupling
reaction conditions (Scheme 2).8
The preparation of a desired precursor for such a study is
based on our finding that a diaryldiazomethane 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 while leaving the diazo
group intact. For instance, bis(2,4,6-tribromophenyl)diazo-
methane survives under Sonogashira coupling reaction
conditions,8 leading to bis(2,6-dibromo-4-trimethylsilyleth-
ynylphenyl)diazomethane.9 This means that diazo compounds
can be used as a building block to construct a complicated
polydiazo compound.
Scheme 2
The starting diazo compound used in this study was
[9-{10-phenyl}anthryl](4-bromo-2,6-dimethylphenyl)diazo-
methane (1-N2), which was prepared according to the
procedure outlined in Scheme 1; this compound can generate
a fairly persistent triplet carbene.10,11 Treatment of 1-N2 with
(4) Platz, M. S.; Wright. B. B. J. Am. Chem. Soc. 1983, 105, 628. See
also: Trozzolo, A. M.; Murray, R. W.; Smolinsky, G.; Yager, W. A.;
Wasserman, E. J. Am. Chem. Soc. 1963, 85, 2526. Wasserman, E.; Murray,
R. W.; Yager, W. A.; Trozzolo, A. M.; Smolinky, G. J. Am. Chem. Soc.
1967, 89, 5076. Itoh, K. Chem. Phys. Lett. 1967, 1, 235.
(5) Seeger, D. E.; Berson, J. E. J. Am. Chem. Soc. 1983, 105, 5146.
Seeger, D. E.; Lahti, P. M.; Rossi, A. R.; Berson, J. E. J. Am. Chem. Soc.
1986, 108, 1251.
(6) Kalgutkar, R. S.; Lahti, P. M. J. Am. Chem. Soc. 1997, 119, 4771.
(7) Regitz, M.; Maas, G. Diazo Compounds-Properties and Synthesis;
Academic Press: Orlando, 1986.
(8) Sonogashira, K. In ComprehensiVe Organic Synthesis; Trost, B. M.,
Fleming, I., Eds.; Pergamon Press: Oxford, UK, 1991; Vol. 3, pp 521-
549.
(9) Tomioka, H.; Hattori, M.; Hirai, K.; Sato, K.; Shiomi, D.; Takui, T.;
Itoh, K. J. Am. Chem. Soc. 1998, 120, 1106.
(10) 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.
(11) 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.; JAI Press: Greenwich, CT, 1998; Vol. 2, pp
175-214. (c) Tomioka, H. In Carbene Chemistry; Bertrand, G., Ed.; Fontis
Media S. A.: Lausanne, 2002; pp 103-152.
Those reactions are realized because the diazo functional
groups in the present system are well shielded by two
(12) Hurst, D. T.; McInnes, A. G. Can. J. Chem. 1965, 43, 2004.
Org. Lett., Vol. 6, No. 5, 2004
848

dimethyls on the phenyl group as well as two peri-hydrogens
on the anthryl ring and, hence, are relatively stable for a
diazo group. The bis(diazo) compound thus obtained is also
relatively stable and could be purified by repeated chroma-
tography on a gel permeation column without any appreciable
decomposition.
E ) 0.000 cm-1. We, therefore, assigned the signals to the
quintet biscarbene, 3 (Figure 2). To estimate the thermal
5
Photolysis of the bis(diazo) compound 3-2N2 in a 2-meth-
yltetrahydrofuran (2-MTHF) solid solution was performed
at 113 K in an ESR cavity with light from a high-pressure
mercury lamp attached with a cut filter (λ > 350 nm). The
ESR spectrum (Figure 1) after photolysis was completely
Figure 1. (a) ESR spectra obtained by irradiation of bis(diazo)
compound 3-2N2 in 2-methyltetrahydrofuran at 77 K. (b) Simulated
spectra of bis(carbene) 53 with S ) 2, g ) 2.003, D ) 0.047 cm-1
,
Figure 2. (a) ESR spectra of 53 observed at 113 K and (b-e) the
same sample observed at 113 K after warming to (b) 120, (c) 125,
(d) 130, and (e) 180 K.
and E ) 0.000 cm-1
.
different from that observed by the photolysis of the
monodiazo compound 2-N2-TMS and showed a set of fine
structure lines at 181, 260, 299, 345, 376, and 398 mT with
rather small signal spacing. Weak signals at 140, 238, and
421 mT are similar to those observed in the photolysis of
the monodiazo compound and, hence, are attributable to the
triplet monocarbene (D ) 0.195 cm-1, E ) 0.00461
cm-1)10,14 presumably formed as a result of the incomplete
photolysis of the bisdiazo compound. The smaller signal
spacing observed for the major spectrum, in comparison to
that for the triplet monocarbene, is consistent with the
tendency that, as the spin multiplicity became higher, the D
value became smaller.15 Indeed, the major signals are well
reproduced by computer simulation16 employing a quintet
Hamiltonian with S ) 2, g ) 2.003, D ) 0.047 cm-1, and
stability of the signals, the temperature at which the quintet
signals disappear was measured. Thus, the 2-MTHF glass
containing 3 was warmed gradually in 10 K increments to
5
a desired temperature, allowed to stand at this temperature
for 5 min, and recooled to 113 K to measure the ESR again.
The signals started to disappear when the 2-MTHF glass was
warmed to around 130 K and disappeared completely at
around 160 K. This is to be compared with that observed
for septet state 1,3,5-tris(phenylmethylene)benzene, which
has been shown to be persistent only up to 50 K in rigid
glass.17 Significant thermal stability was thus noted. Note
that the ESR signals of triplet monocarbene from 2-N2-TMS
also decayed at around 160 K. Thus, the thermal stability
was not deteriorated by this modification.
The present study shows another example in which a
precursor for persistent triplet carbene can be used as a
(13) Lovell, J. M.; Joule, J. A. Synth. Commun. 1997, 27, 1209.
(14) 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.
(16) (a) Teki, Y. Thesis, Osaka City University, Osaka, Japan, 1985.
(b) Takui, K. In Molecular Magnetism in Organic-Based Materials; Lahti,
P. M., Ed.; Marcel Dekker: New York, 1999.
(17) Matsuda, K.; Takahashi, K.; Inoue, K.; Koga, N.; Iwamura, H. J.
Am. Chem. Soc. 1995, 117, 5550.
(15) Teki, Y.; Takui, T.; Yagi, H.; Itoh, K.; Iwamura, H. J. Chem. Phys.
1985, 83, 539.
Org. Lett., Vol. 6, No. 5, 2004
849

building block to construct a more complicated polydiazo
compound that eventually generated a high-spin polycarbene
with remarkably high thermal stability. It is potentially
possible to introduce five diazo units at maximum on an
anthracene ring so as to generate persistent pentakis(carbene)
in the high-spin ground state. A study along this line is under
progress.
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 appreci-
ated.
Supporting Information Available: Preparation of bis-
(diazo) compound 3-N2. This material is available free of
charge via the Internet at http://pubs.acs.org.
Acknowledgment. The authors are grateful to the Min-
istry of Education, Culture, Sports, Science, and Technology
OL049877J
850
Org. Lett., Vol. 6, No. 5, 2004