Synthesis of Urea Picket Porphyrins and Their Use in the Elucidation of the Role Buried Solvent Plays in the Selectivity and Stoichiometry of Anion Binding Receptors

The synthesis of α,α-5,10-diurea and α,α,α-5,10,15-triurea picket porphyrins are detailed in this report.
In previous reports, these porphyrins, along with α,α,α,α-5,10,15,20-tetraurea picket porphyrin, were
used to demonstrate the important role one buried solvent molecule plays in the selectivity and
stoichiometry of binding inorganic anions. Building on prior work, this report discusses the results of
acetate anion binding studies between tetra- and diurea picket porphyrins (the latter does not contain a
buried solvent molecule in the anion−receptor complex), compares differences in thermodynamic data
obtained from van't Hoff plots of a porphyrin anion receptor able to utilize buried solvent in its binding
motif with one that does not, and compares the crystal structure of a tetraurea porphyrin 1−chloride
anion complex that contains buried solvent with new X-ray crystal structures of tetraurea porphyrin
1−dichloride or bisdihydrogenphosphate anion complexes that contain no buried solvent. Data from our
previous work, and the work described herein, demonstrates that one buried solvent molecule provides
stability to the receptor−anion complex that is similar in energy to a moderately strong hydrogen bond.