Calix[<i>n</i>]bispyrrolylbenzenes: Synthesis, Characterization, and Preliminary Anion Binding Studies

<jats:title>Abstract</jats:title><jats:p>A series of novel calixpyrrole‐like macrocycles, calix[<jats:italic>n</jats:italic>]bis(pyrrol‐2‐yl)benzene (calix[<jats:italic>n</jats:italic>]BPBs, <jats:italic>n</jats:italic>=2–4) <jats:bold>9 a</jats:bold>–<jats:bold>11 a</jats:bold>, have been synthesized by means of the TFA‐catalyzed condensation reaction of bis(pyrrol‐2‐yl)benzene <jats:bold>8 a</jats:bold> with acetone. Calix[2]BPB <jats:bold>9 a</jats:bold> represents an expanded version of calix[4]pyrrole in which two of the four <jats:italic>meso</jats:italic> bridges are replaced by benzene rings. By contrast, systems <jats:bold>10 a</jats:bold> and <jats:bold>11 a</jats:bold>, which bear great considerable to calixbipyrroles <jats:bold>2</jats:bold> and <jats:bold>3</jats:bold>, represent higher homologues of the basic calix[<jats:italic>n</jats:italic>]BPB motif. Solution‐phase anion binding studies, carried out by means of <jats:sup>1</jats:sup>H NMR spectroscopic titrations in [D<jats:sub>2</jats:sub>]dichloromethane and isothermal titration calorimetry (ITC) in 1,2‐dichloroethane, reveal that <jats:bold>9 a</jats:bold> binds typical small anions with substantially higher affinities than <jats:bold>1</jats:bold>, even though the same number of hydrogen bonding donor groups are found in both compounds. The basic building block for <jats:bold>9 a</jats:bold>, benzene dipyrrole <jats:bold>8 a</jats:bold>, also displays a higher affinity for anions than the building block for <jats:bold>1</jats:bold>, dimethyldipyrromethane <jats:bold>16</jats:bold>. Structural studies, carried out by single‐crystal X‐ray diffraction analyses, are consistent with the solution‐phase results and reveal that <jats:bold>9 a</jats:bold> is able to stabilize complexes with chloride and nitrate in the solid state. Structures of the PF<jats:sub>6</jats:sub><jats:sup>−</jats:sup> and NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup> complexes of <jats:bold>10 a</jats:bold> were also solved as were those of the acetone adduct of <jats:bold>9 a</jats:bold> and the ethyl acetate adduct of <jats:bold>11 a</jats:bold>.</jats:p>