Synthesis and Characterization of Carboxylate Complexes of SnIV Porphyrin Monomers and Oligomers

Most of the porphyrin‐recognition chemistry we have investigated previously has centred on kinetically labile metal–ligand interactions, such as ZnN and RuN. Our interest in the broader scope of molecular recognition required a metal with the ability to specifically recognise non‐nitrogen‐based ligands, with a significantly different binding interaction to distinguish it from nitrogen‐based analogues. In this report we describe interactions of SnIV porphyrins that bind oxygen‐based ligands and for which the SnIVO bond is in slow exchange on the NMR timescale. A series of carboxylate complexes is employed to highlight the structural/geometric features of porphyrin monomers and cyclic oligomers. Where more than one porphyrin unit is present in a molecular scaffold, we report the effect of carboxylate binding on the complex when the two porphyrins contain different metals (typically SnIV and ZnII). The unexpected spectroscopic and structural properties of the Sn2(9‐anthroic acid)porphyrin dimer are also reported. A coordination interaction that can be exploited in the construction of supramolecular complexes comes from the very slow dissociation of carboxylate ligands from newly synthesised porphyrin monomers and cyclic oligomers. The solution‐state geometry of a series of carboxylate–porphyrin complexes is described, as well as how anthracene–porphyrin interactions can overcome the usual geometric preferences in a cyclic host (see scheme).