Metallation of a cyclic chlorophyll hetero-dyad, and the optical properties of synthetic metallo-dyads
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A cyclic chlorophyll hetero-dyad 1-H2H2, prepared by double ester linking of two structurally different pyropheophorbide-a moieties through 3-CH2OCO-132′ and 172-COOCH2-3′, was metallated with zinc and copper to give mono and di-metallated complexes 1-MH2 or 1-H2M and 1-MM. The metallation proceeded stepwise and regioselectively, with predominant synthesis of one of the two mono-metallated complexes 1-MH2 as intermediate. The di-zinc complex produced, 1-ZnZn, was demetallated exclusively via the same mono-zinc complex 1-ZnH2 as was the major intermediate during metallation. Visible and/or circular dichroism spectra of 1-H2H2, 1-MH2, 1-H2M, and 1-MM (M = Ni, Cu, or Zn) were measured in organic solvents. Intramolecular interaction of chlorin chromophores is discussed and compared with that of the corresponding monomeric species.
KeywordsChlorophyll Dimer Intramolecular interaction Metal complex Regioisomer
We thank Dr Toru Oba of Utsunomiya University for useful discussion. This work was partially supported by a Grant-in-Aid for Scientific Research (A) (No. 22245030) from the Japan Society for the Promotion of Science (JSPS).
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