Templated synthesis of catenanes incorporating Zn(II) or Rh(III)-complexed porphyrins: the coordination chemistry-only approach

Abstract

Porphyrin-containing [2]catenanes were obtained from relatively simple organic precursors thanks to "coordination chemistry-only". When the central porphyrin metal is Zn2+ the [2]catenanes were assembled in two steps by using Cu(I)–N interactions to assemble acyclic complexes and Zn(II)–N interactions to generate rings. These sophisticated architectures were obtained in excellent yield since the formation of the thermodynamic products is favored over that of kinetic products. This also explains why a perfect fit in terms of distances and angles between the components to assemble leads to highly stable coordination chemistry-assembled species. When a second row metal with an inert coordination sphere, like Rh(III) was chosen as metal centre of the porphyrins, direct metalation of porphyrinic compounds with [Rh(CO)2Cl]2 was not met with success when the bidentate chelate used as connector was metal free. A three-step strategy was used for the synthesis of a tetra-rhodiumporphyrin[2]-catenane: (i) copper(I)-driven entwining of two free-base porphyrin-bearing bidentate chelates followed (ii) by insertion of rhodium in the porphyrin nuclei and finally (iii) cyclisation via formation of N-Rh coordination bonds.