| Institution: | 1. Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502 Japan;2. Center for Coordination of Research Facilities, Institute for Research Promotion, Niigata University, Nishi-ku, Niigata, 950-2181 Japan
Institute for Molecular Science, 38 Nishigo-naka, Myodaiji, Okazaki, 444-8585 Japan |
| Abstract: | 2,18-Bis(dicyanomethyl)-substituted NiII porphyrin 8 and ZnII porphyrin 11 were prepared and subjected to oxidation with PbO2 in CH2Cl2 at 298 K to give cyclophane-type chlorin dimers ( 9 )2 and ( 12 )2 as a consequence of double recombination of biradicals 9 and 12 , respectively. Dimer ( 9 )2 takes a syn-conformation of two distorted NiII chlorins but ( 12 )2 takes an anti-conformation of relatively planar ZnII chlorins. At 298 K, dimer ( 9 )2 is stable and its 1H NMR spectrum is sharp but becomes broad at high temperature, while the 1H NMR spectrum of ( 12 )2 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 )2 is much less than that of ( 9 )2. The involvement of diradicals in dynamic covalent chemistry has been suggested by thermal scrambling of hetero dimer ( 16 )2 to give homo dimers ( 9 )2 and ( 15 )2. |
