π-conjugated skeleton of triphenylene, which has two rigid
pathways for the interaction, the substituted three radicals’
unpaired electrons could strongly interact and a spin defect
which interrupts the interaction would not be vital, leading
to a triplet molecule at room temperature.
Several groups reported the synthesis of symmetrical,
unsymmetrical, and functionalized triphenylene derivatives.
Some of the triphenylene derivatives are prepared by the
trimerization of halogenated aryls using Pd coupling11 and
lithiation.12 The unsymmetrical triphenylenes13 are also
synthesized by the coupling of the biphenyl precursor and
the aryl substituted with different substituents. Among these
synthetic routes of the triphenylene derivatives, the oxidative
trimerization of phenyl ether14 is one of the efficient routes
to obtain a triphenylene with substituent groups on the 2, 6,
and 10 positions, which possibly produce the ferromagnetic
coupling.
This paper describes a room-temperature robust quartet
molecule, 2,6,10-tris(dianisylaminium)-3,7,11-tris(hexyloxy)-
triphenylene 13+. We selected, for the first time, the 2,6,-
10-substituted triphenylene as a planar and π-conjugated
ferromagnetic coupling core for the high-spin alignment. The
2,6,10-position of the triphenylene was very appropriate for
significantly reducing both the steric hindrance of the radical
moieties and electrostatic repulsion between the cationic
radicals, which lead to the chemical stable molecule 13+ with
the spin alignment of S (spin quantum number) ) 3/2.
The triphenylene core 3 was prepared by the oxidative
trimerization of the 2-hexyloxyanisole 2 with FeCl3 (Scheme
1).19 The methoxy groups of 3 were converted to triflate
Scheme 1
For the molecular design of high-spin molecules, the
second requisite is the selection of a stable organic radical
species as the spin source. Molecules substituted with the
triarylmethane radical and the phenoxyl radical have been
studied;15,16 however, their high-spin states were observed
only in a low-temperature range because of the chemical
instability of these radical species. Chemically stable radical
species are desired in such high-spin molecules to raise the
temperature range of the spin alignment and possibly use
them as a module for a molecular-based material. From
among the list of radical species, the triarylaminium radical
is a favorable candidate for the spin source which could fulfill
the criteria of having both a substantial chemical stability
even at room temperature and a strong spin polarization for
spin alignment.1f,17 From such a viewpoint, a series of high-
spin aminium radical modules have been synthesized;18
however, they often lacked stability at room temperature and
the quantitative radical (spin) generation because of their high
oxidation potential and/or side reactions.
(11) Pena, D.; Perez, D.; Guitian, E.; Castedo, L. Org. Lett. 1999, 1,
1555.
(12) Heaney, H.; Mann, F. G.; Millar, T. J. Chem. Soc. 1957, 3930.
(13) Borden, N.; Bushby, R. J.; Cammidge, A. N. J. Chem. Soc., Chem.
Commun. 1994, 465.
(14) Naarmann, H.; Hanack, M.; Mattmer, R. Synthesis 1994, 477.
(15) (a) Rajca, A.; Wongsriratanakul, J.; Rajca, S. Science 2001, 294,
1503. (b) Rajca, A.; Wongsriratanakul, J.; Rajca, S. J. Am. Chem. Soc. 2004,
126, 6608.
(16) (a) Nishide, H.; Nambo, M.; Miyasaka, M. J. Mater. Chem. 2002,
12, 3578. (b) Kaneko, T.; Makino, T.; Miyaji, H.; Teraguchi, M.; Aoki, T.;
Miyasaka, M.; Nishide, H. J. Am. Chem. Soc. 2003, 125, 3554.
(17) (a) Stickley, K. R.; Selby, T. D.; Blackstock, S. C. J. Org. Chem.
1997, 62, 448. (b) Wienk, M. M.; Janssen, R. A. J. J. Am. Chem. Soc.
1997, 119, 4492. (c) Bushby, R. J.; Gooding, D. J. Chem. Soc., Perkin
Trans. 2 1998, 1069. (d) Selby, T. D.; Blackstock, S. C. J. Am. Chem. Soc.
1999, 121, 7152. (e) Goodson, F. E.; Hauck, S. I.; Hartwig, J. F. J. Am.
Chem. Soc. 1999, 121, 7527. (f) van Meurs, P. J.; Janssen, R. A. J. J. Org.
Chem. 2000, 65, 5712. (g) Nelsen, S. F.; Trieber, D. A., II.; Ismagilov, R.
F.; Teki, Y. J. Am. Chem. Soc. 2001, 123, 5684. (h) Yamamoto, K.; Higuchi,
M.; Shiki, S.; Tsuruta, M.; Chiba, H. Nature 2002, 415, 509. (i) Michinobu,
T.; Inui, J.; Nishide, H. Org. Lett. 2003, 5, 2165. (j) Murata, H.; Takahashi,
M.; Namba, K.; Takahashi, N.; Nishide, H. J. Org. Chem. 2004, 69, 631.
(k) Murata, H.; Yonekuta, Y.; Nishide, H. Org. Lett. 2004, 6, 4889. (l)
Wu, J.; Baumgarten, M.; Debije, M. G.; Warman, J. M.; Mu¨llen, K. M.
Angew. Chem., Int. Ed. 2004, 43, 5331.
groups in compound 5 via selective ether cleavage and
esterification. The 2,6,10-tris(p-dianisylamino)-3,7,11-tris-
(hexyloxy)triphenylene 1 was obtained by Pd coupling of
the triflates 5 with dianisylamine in the presence of Cs2CO3.20
The yields of the trimerization and ether cleavage were 10
and 75%, respectively, which were comparable to those
previously reported19 for the corresponding reactions and
fairly good for obtaining 1. For the process from 5 to 1, the
triflate is a good leaving group to be substituted with the
dianisylamine by the Pd coupling. 5 may be an effective
intermediate to yield other radical (phenoxyl, galvinoxyl,
nitroxide, and nitronyl nitroxide) precursor-substituted tri-
phenylenes. The NMR, IR, and mass spectra of 1 supported
its structure. For example, two singlet signals of the protons
and triplet signals of the hexyloxy groups on the triphenylene
(18) (a) Selby, T. D.; Blackstock, S. C. Org. Lett. 1999, 1, 2053. (b)
Hauck, S. I.; Lakshmi, K. V.; Hartwig, J. F. Org. Lett. 1999, 1, 2057. (c)
Selby, T. D.; Stickley, K. R.; Blackstock, S. C. Org. Lett. 2000, 2, 171. (d)
Ito, A.; Ono, Y.; Tanaka, K. Angew. Chem., Int. Ed. 2000, 39, 1072.
(19) Boden, N.; Bushby, R. J.; Martin, P. S.; Evans, S. D.; Owens, R.
W.; Smith, D. A. Langmuir 1999, 15, 3790.
(20) (a) A° hman, J.; Buchwald, S. L. Tetrahedron Lett. 1997, 38, 6363.
(b) Wolfe, J. P.; Buchwald, S. L. J. Org. Chem. 1997, 62, 1264.
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