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 Sn-IV porphyrins that bind oxygen-based ligands and for which the Sn-IV-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 Sn-IV and Zn-II). The unexpected spectroscopic and structural properties of the Sn-2(9-anthroic acid)-porphyrin dimer are also reported.