Pseudo[ n ]-pillar[5]arenes: Synthesis, Structures, and Host-Guest Binding Properties.

[1 n ]Paracyclophane has been known for nearly 40 years, but its derivatives and properties are understudied in comparison to those of other macrocyclic compounds. By the modification of pillar[5]arene, we successfully obtained five electron-rich pentagonal macrocycles (pseudo[ n ]-pillar[5]arenes, n = 1-4) with the decrease of substituted phenylenes one after another, achieving the partial derivatization of [1 5 ]paracyclophane skeleton at its phenylene sites. Pseudo[ n ]-pillar[5]arenes ( P[ n ]P[5]s ) served as a kind of macrocyclic host to form complexes with various guests, such as dinitriles, dihaloalkanes, and imidazolium salt, in a 1:1 host-guest stoichiometric ratio. The binding constants with the guest gradually reduce along the decrease of substituted phenylene segments from host P[1]P[5] to P[4]P[5] . It is worthy to note that P[ n ]P[5]s can adjust their conformations to the "pillar-like" shape effectively when binding with succinonitrile in the solid state.