An oxacalix[2]arene[2]pyrimidine-bis(Zn-porphyrin) tweezer as a selective receptor towards fullerene C70

An oxacalix[2]arene[2]pyrimidine-bis(ZnII-porphyrin) conjugate was readily prepared via nucleophilic aromatic substitution of a phenolic AB3-Zn-porphyrin on the upper rim of a (1,3-alternate) 5,17-bis(methylsulfonyl)oxacalix[4]arene precursor. Efficient 1:1 complex formation between the 'jaws' bisporphyrin tweezer and fullerene C70 was evidenced by 1H NMR titrations (K = 3.0 × 104 M−1), while no detectable complexation could be observed with C60. On the other hand, an analogous oxacalix[4]arene-bis(Cu-corrole) conjugate did not show any measurable (C60 or C70) fullerene binding.

The versatility of oxacalix[m]arene[m]pyrimidines as building blocks for the construction of sophisticated supramolecular receptors has been illustrated by the synthesis of bisporphyrinoid molecular tweezers towards fullerene complexation. 1H NMR titrations revealed selective binding of C70 (K = 3.0 × 104 M−1) for an oxacalix[2]arene[2]pyrimidine-bis[ZnII-porphyrin] conjugate.