ORGANIC LETTERS
m-Phenylene-Linked Aromatic Poly(aminium cationic radical)s: Persistent High-Spin Organic Polyradicals
2003 Vol. 5, No. 12 2165-2168
Tsuyoshi Michinobu, Jun Inui, and Hiroyuki Nishide* Department of Applied Chemistry, Waseda UniVersity, Tokyo 169-8555, Japan
[email protected] Received April 11, 2003
ABSTRACT
High molecular weight and networked aromatic polyamines prepared by palladium-catalyzed polycondensation were oxidized to yield the corresponding poly(aminium cationic radical)s, which displayed a substantial stability and an intramolecular ferromagnetic interaction of eight or nine spins.
High-spin polyradicals have been extensively investigated as possible candidates for organic ferromagnetic materials.1 The design of such molecules is based on the precise connectivity of robust spin sources and nondisjointed couplers in a π-conjugated polymer. It was recently reported that the highly cross-linked polyradical with a triarylmethine radical as a spin source showed a very large magnetic moment and magnetic ordering at low temperature.2 However, the triarylmethine radical can survive only below 200 K, so chemically stable radical species are desired in such a networked polyradical to raise the magnetic ordering temperature and provide feasibility as a material. Aromatic polyamines are an attractive material for this purpose because the aromatic amines are expected to be a prominent spin carrying site with both a substantial chemical stability even (1) (a) Lahti, P. M. Magnetic Properties of Organic Materials; Marcel Dekker: New York, 1999. (b) Itoh, K.; Kinoshita, M. Molecular Magnetism; Kodansha and Gordon and Breach: Tokyo and Amsterdam, 2000. (c) Miller, J. S.; Drillon, M. D. Magnetism: Molecules to Materials II; Wiley-VCH: Weinheim, Germany, 2001. (d) Rajca, A. Chem. Eur. J. 2002, 8, 4834. (2) (a) Rajca, A.; Rajca, S.; Wongsriratanakul, J. J. Am. Chem. Soc. 1999, 121, 6308. (b) Rajca, A.; Wongsriratanakul, J.; Rajca, S. Science 2001, 294, 1503. 10.1021/ol0346281 CCC: $25.00 Published on Web 05/14/2003
© 2003 American Chemical Society
at room temperature and large spin polarization after a oneelectron removal.3 A series of oligoradicals have been synthesized to evaluate the radicals,4,5 and p-phenylenediamine-based cationic radicals were found to be more stable than the triarylaminium cationic radicals.6 The attempted integration of the p-phenylenediamine-based cationic radical into linear and two-dimensional polyradicals was tried;7 however, there has been no report on a successful radical generation to yield the chemically stable and high-spin poly(aminium cationic radical)s. By adjusting the monomer geometry and the feed ratio during the polycondensation and utilizing the effect of trifluoroacetic acid (TFA) on aromatic polyamines, we now prepared, for the first time, twodimensional networked and persistent polyradicals, in which p-phenylenediamine-based cationic radicals effectively interacted through 1,3-phenylene or 1,3,5-benzenetriyl couplers (3) (a) Bushby, R. J.; Ng, K. M. Chem. Commun. 1996, 659. (b) Bushby, R. J.; McGill, D. R.; Ng, K. M.; Taylor, N. J. Mater. Chem. 1997, 7, 2343. (c) Bushby, R. J.; Gooding, D. J. Chem. Soc., Perkin Trans. 2 1998, 1069. (d) Higuchi, M.; Shiki, S.; Yamamoto, K. Org. Lett. 2000, 2, 3079. (e) Yamamoto, K.; Higuchi, M.; Shiki, S.; Tsuruta, M.; Chiba, H. Nature 2002, 415, 509.
to bring about their innate high-spin character with an average spin quantum number (S) of 8/2 to 9/2. The networked aromatic polyamines were prepared by using the palladium-catalyzed amination of two multifunctionalized monomers (Scheme 1). The bifunctionalized
Scheme 1 a
a Reagents and conditions: (a) Pd (dba) , P(t-Bu) , NaOtBu, 2 3 3 toluene, 100 °C, 24 h.
polymer with a preferably higher molecular weight and bearing all the terminal bromide groups.8 Although the reaction of N,N′-diaryl-p-phenylenediamine and 1,3,5-tribromobenzene gave a yellow gel and trace amounts of a soluble fraction with the number average molecular weight (Mn) of
