Adinarayana B, Kato Kenichi, Shimizu Daiki, Tanaka Takayuki, Furukawa Ko, Osuka Atsuhiro
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan.
Center for Coordination of Research Facilities, Institute for Research Promotion, Niigata University, Nishi-ku, Niigata, 950-2181, Japan.
Angew Chem Int Ed Engl. 2020 Mar 9;59(11):4320-4323. doi: 10.1002/anie.201914480. Epub 2020 Jan 29.
2,18-Bis(dicyanomethyl)-substituted Ni porphyrin 8 and Zn porphyrin 11 were prepared and subjected to oxidation with PbO in CH Cl at 298 K to give cyclophane-type chlorin dimers (9) and (12) as a consequence of double recombination of biradicals 9 and 12, respectively. Dimer (9) takes a syn-conformation of two distorted Ni chlorins but (12) takes an anti-conformation of relatively planar Zn chlorins. At 298 K, dimer (9) is stable and its H NMR spectrum is sharp but becomes broad at high temperature, while the H NMR spectrum of (12) is considerably broad even at 298 K but becomes sharper at low temperature. These results indicate that the chlorin dimers dissociate to radical species, but the activation barrier of the dissociation of (12) is much less than that of (9) . The involvement of diradicals in dynamic covalent chemistry has been suggested by thermal scrambling of hetero dimer (16) to give homo dimers (9) and (15) .
制备了2,18-双（二氰基甲基）取代的镍卟啉8和锌卟啉11，并于298 K下在CH₂Cl₂中用PbO进行氧化，分别通过双自由基9和12的双重重组得到环芳型二氢卟吩二聚体（9）和（12）。二聚体（9）呈现两个扭曲镍二氢卟吩的顺式构象，而（12）呈现相对平面的锌二氢卟吩的反式构象。在298 K时，二聚体（9）稳定，其¹H NMR谱尖锐，但在高温下变宽，而（12）的¹H NMR谱即使在298 K时也相当宽，但在低温下变尖锐。这些结果表明二氢卟吩二聚体解离为自由基物种，但（12）解离的活化能垒远小于（9）的。通过杂二聚体（16）热重排生成同二聚体（9）和（15），表明双自由基参与了动态共价化学。
