ELSEVIER Synthetic Metals 103 (1999) 2304-2305 Generation and reactivity of 2,4,&triphenylpyridinyl radicals linked by alkyl chains IS Matsumotoa, M. Odaa, M. Kozakib, K. Satob, T. Takuib, and K. Okadab* a Graduate School of Science, OsakaUniversity, Toyonaka, Osaka 560-0043, Japan b Department of Chemistry, Graduate School of Science,Osaka City University, Sugimoto, Sumiyoshl-ku,Osaka558-8585, Japan Abstract A series of bis(2,4,6-triphenylpyridinyl) diradicals l-6 linked by alkanediyl [ 1 for n (number of methylene) = 2,2 for n = 3, 3 for n = 4, 4 for n = 5, 5 for n = 8, 6 for puns-1,4-cyclohexanediyl] were preparedby reduction of the corresponding bispyridinium salts with 3%- sodium amalgam. The diradicals 1-5 were moderately stable at room temperature under inert atmosphere. Although the diradical 6 was unstable at room temperature and underwent a facile C-N bond cleavage, the diradical persistedwhen the reduction of the bispyridinium salt was carried out at -30 ‘C under inert atmosphere. The triplet states for all these diradicals were observedand the exchange interaction was studied by temperature dependence of the ESR signal intensity for l-3 and 6. The resultsof the exchangeinteraction are summarized asfollows: 1 in singlet ground state with A&S-T> 1.7 kJ/mol, 2, 3 in the singlet ground state with hES.T c 230 J/mol, and 6 in the triplet ground state or in a degeneratesinglet state. Keyworn!s:Heterocyde Synthesis, Electron spin resonance, UV-Vis-NIR absorption 1. Introduction Recently, a number of organic high-spin molecules has been prepared and their exchange interaction has been studied in relation to molecular magnetism. In contrast to many organic high-spin molecules with a linkage of n-conjugated systems, little studieshave been achievedon those linked with o-frames [l]. In the course of our study of pyridinyl radical 121, we now report preparation, characterization, and reactivity (for 6) of bis(2,4,6- triphenylpyridinyl) diradicals l-6 linked by alkanediyl. 1: n = 2, 2: n = 3, 3: n = 4, 4: n = 5, 5: n = 6 6 2. Preparation of diradicals l-6 The bispyridinyl diradicals l-6 were prepared from the corresponding dipyridinium salts which were obtained from diaminoalkanes and 2,4,6-triphenylpyrylium tetrafluoroborate (Scheme 1). The obtained dipyridinium salts l-5 were reduced with 3 % sodium amalgam in acetonitrile under degassed condition. The reduction was monitored using electronic spectrum. Figure 1 shows a typical example for the reduction of la, Each spectrum are recorded as a function of the contact time with the sodium amalgam. The colorless solution of la turned reddish purple (576 nm). The new absorption band are characteristic for 1-methyl-2,4,6+iphenylpyridinyl radical [2]. When the absorption of the dication la (317 nm) disappeared (after 120 sec. in Fig. l), the absorption was assigned to be due to the diradical 1. The same procedure was used for the preparation of 2-5. These diradieal l-5 had moderate stability and the absorption gradually weakened by standing for several hours at mom temperature under degassed conditions. Scheme 1 Th W43 Ph 1) Et@ / CHC13 2) AcOH c la; 14 %, 2a; 31 %, 3a; 50 %, - 4a; 57 %, 5a; 69 %, 6s; 47 % 2.0 r 317 nm . 120 sec. 100 sec. 80 sec. 60 sec. 40 sec. 0 sec. 300 400 500 600 700 800 Wavelengtn [nrnl Fig. 1, UV-vis spectral change upon reduction of la to form diradical 1. 0379-6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: SO379-6779(98)00647-X