Dioxabenzosapphyrin: A new benzodifuran-derived sapphyrin analogue

The synthesis and characterization of a new sapphyrin analogue, dioxabenzosapphyrin, are reported. The benzodifuran moiety upon which this system is based leads to the incorporation of two oxygen atoms within the central macrocyclic core, thus replacing two protonated nitrogen centers found in normal pentaaza sapphyrin derivatives, including those derived from benzodipyrroles. As expected, the loss of these two NH hydrogen bond donor sites greatly reduces the anion affinity for the diprotonated form, even though the overall charge is the same as in the corresponding sapphyrins. Interestingly, dioxabenzosapphyrin, but not the corresponding all-aza systems, is found to bind neutral guests, such as phenol and 4-nitrophenol, albeit weakly. This latter finding highlights a potentially new application for core-modified expanded porphyrin derivatives, namely, as receptors for hydrogen bond donating neutral substrates.