Molecular Recognition Properties of Biphen[4]arene.

Biphen[n]arenes (n=3, 4) are a new family of macrocyclic hosts. Here, we describe the molecular recognition behavior of hydroxylated biphen[4]arene (OHBP4) for the first time. A series of cationic guests with different sizes and shapes, including quaternary ammonium salts (1⋅PF6 and 2⋅PF6 ), pyridinium-based guests (3⋅2 PF6 -6⋅2 PF6 ), and cobaltocenium hexafluorophosphate (7⋅PF6 ), were chosen as model guest molecules. OHBP4 exhibits good selectivity towards the 2,7-dibutyldiazapyrenium bis(hexafluorophosphate) (4⋅2 PF6 ) axle to form a [2]pseudorotaxane-type complex. In contrast, hydroxylated biphen[3]arene (OHBP3) cannot bind with this big guest. In addition, OHBP4 strongly interacts with adamantane derivative 2⋅PF6 and cobaltocenium 7⋅PF6 , which have tridimensional shape and relatively large size. The association constant of the 7+ ⊂OHBP4 complex in 1:1 (v/v) [D6 ]acetone/CD2 Cl2 solution is up to 3100±300 m-1 .