Monomeric Chiral and Achiral Basket-Handle Porphyrins: Synthesis, Structural Features, and Arrested Tautomerism

Chiral and achiral basket-handle
porphyrins (BHPs) with different p-xylene straps
and peripheral solubilizing groups were
synthesized using a previously established synthetic approach. Subsequent
modification, functionalization, and metalation of the tetrapyrrolic
macrocycle yielded more than 80 BHPs. The chiral representatives were
resolved into their enantiomers, whose absolute configurations were
determined by comparison of their ECD spectra with other experimental
or quantum chemically calculated spectra. NMR studies and coupled-cluster
calculations proved that the free base BHPs, although highly symmetric,
exhibited the phenomenon of “arrested tautomerism”.
Comparison of the solid-state structures of three metalated BHPs offered
detailed insight into their three-dimensional shape. Finally, directly
linked dimeric porphyrins with a BHP subunit were synthesized from
functionalized BHPs to prove their value as synthetic building blocks.