高安定性リン複素環一重項ビラジカルおよび関連分子系の合成と性質

抄録

Whereas biradicals are generally observed only under cryogenic inert conditions, highly stabilized 1,3-diphosphacyclobutane-2,4-diyls, phosphorus congeners of cyclobutane-1,3-diyl, can be stored at room temperature and even in air. We succeeded in establishing a promising synthetic protocol for the extremely stable biradicals by utilizing a bulky phosphaalkyne Mes^*C≡P(Mes^*=2,4,6-tri-t-butylphenyl). The singlet ground state biradicals were characterized by spectroscopies including NMR, and the X-ray structural parameters indicated effects of the phosphorus atoms and sterically encumbered aryl substituents. Conversion into the cyclic phosphorane and thermal ring-expansion were facilitated by the presence of amino- and acyl substituents, respectively. Dual hydrogen loadings on the biradical skeleton were accomplished to afford cyclobutadiene-like P-heterocycles. Most of the air-stable P-heterocyclic biradicals showed high electron-donating properties, and catenation of two or three biradical units induced unique intramolecular through-space interactions between the biradical chromophores. Stable P-heterocyclic neutral monoradical was successfully obtained by utilizing the biradical synthetic procedures.