Host-Guest Complexation. 38. Cryptahemispherands and Their Complexes

Article abstract of DOI:10.1021/ja00271a031

Syntheses and crystal structures are reported for a new class of hosts, their complexes, and their precursors.The cryptahemispherands 5-8 are composed of molecular modules that are half spherand 1 and half cryptand 3.They were synthesized by the reactions of diacid chloride 20 with cyclic diamines 21-23 to produce diamides 13-16, reduction of which gave the desired hosts 5-8.These diamines were best purified, stored, and handled through their respective hydroborane complexes, 9-12.Hosts 6 and 7 are diastereomeric, as are diamides 14 and 15 and hydroborane complexes 10 and 11.Diamines 6 and 7 equilibrate rapidly at 25 deg C probably by ring inversion of the methoxyl groups to give a 5:1 ratio of 6 over 7.Diamides 14 and 15 equilibrate readily at 90 deg C to give only 14 in detectable amounts.Hydroborane complexes 10 and 11 do not equilibrate at 90 deg C.Cryptahemispherands 5, 6 and 8 formed a variety of complexes with the alkali metal cations, diamides 14 and 16 exhibited a low level of binding power, and hydroborane complexes 10 and 12 had no detectable affinity for the alkali metal cations.Hemispherand 17 was synthesized for comparison purposes.Crystal structures were determined for the isomeric diamides 14 and 15, for hydroborane complex 9, and for alkali cation complexes 5.NaB(Ph)4, 6.KSCN, 8.NaSCN, 8.KSCN, and 8.CsClO4.The trisanisyl modules of all eight compounds possess the same preorganized conformation, with the unshared electron pairs of the three methoxyl groups turned inward and the methyl groups outward.The potential cavities of 9, 14, and 15 are filled inward-turned hydrogens of the ethylene bridges.In the alkali metal ion complexes, the unshared electron pairs of the heteroatoms are all turned inward toward the quest metal ion.The use of CPK molecular models in predicting the structures of complexes is evaluated.