Synthesis of one-dimensional bis-porphyrinic compounds with a transition metal complex as bridging unit

Abstract

Linear multicomponent systems, consisting of two porphyrins attached to a central transition metal center, have been prepared and some of their electron- or energy transfer properties have been studied. Each porphyrin is covalently bound to a bidentate or a terdentate ligand, these coordinating molecules being gathered around the metal to afford the desired structure. The spatial arrangement is such that the porphyrinic components are located at both ends of an axis, the transition metal occupying its center. The edge-to-edge distance between the porphyrins is relatively large (~ 20 to 25 Å) and, due to the rigidity of the connectors, it is very well controlled. Three different strategies have been used to construct such assemblies. In the first approach, the porphyrinic fragments are attached at the back of 2,2′,6′,2″-terpyridine ligands (terpy), on the central position (4′). After reaction with an appropriate metal center (ruthenium(II) or iridium(III)), an octahedral complex is obtained which constitutes the central part of the assembly, whereas the porphyrins are at the periphery of the central complex. The second strategy involves the preparation of a 5,5′-disubstituted 2,2′-bipyridine (bipy) ligand followed by its coordination to ruthenium(II). Subsequently, the porphyrinic nuclei are constructed at both ends of the substituents, leading to a linear geometry with a central complex and two laterally-disposed porphyrins. Finally, a very special ligand has been designed and synthesized, which incorporates two 1,10-phenanthroline nuclei (phen). This ligand can wrap itself around an octahedral center (ruthenium(II)) so as to generate a helical arrangement. Both ends of the single-stranded helix can subsequently be attached to porphyrins.