Supramolecular Metal Arraying in Porphyrin/Phthalocyanine Conjugates for Catalytic Applications

Abstract

Recently, we reported synthesis of porphyrin/phthalocyanine conjugates linked by fourfold rotaxane. In the conjugate, a porphyrin and a phthalocyanine formed a heterodimer in a cofacial fashion (Fig. 1a). [1] The conjugate is a promising platform for supramolecular catalysts based on dinuclear porphyrinoid complexes, because various metal ions to be a functional center are able to be arrayed in the conjugate regioselectively to afford homo- and hetero-dinuclear centers in the conjugate. [2,3] Moreover, these arrays were expanded to hetero-trinuclear arrays (Fig. 1b). [3-6] In this paper, we will present regioselective metal arraying in the conjugate and the supramolecular catalytic functions (Fig. 2). One of the methods to prepare the hetero-dinuclear complexes was to use the difference of metalation rate between porphyrin and phthalocyanine. We found reaction conditions for porphyrin-selective Fe(II) or Ni(II) insertion and phthalocyanine-selective Mn(II) insertion. Subsequent metalation to another porphyrinoid in the conjugate gave a hetero-dinuclear complex. We used these multinuclear complexes in the conjugate as catalysts. The dinuclear iron complex exhibited good catalytic activity in electrochemical reduction of molecular oxygen to water. [7]