Isolation and Structure of an “Imploded” Cryptophane

Abstract

Container crushing: Thermal liberation of the encapsulated guest in a cryptophane has been shown to cause conformational “implosion” in the solid state. The resulting collapsed form is kinetically stable, can be isolated, and its unexpected structure has been elucidated by X‐ray diffraction. It eventually re‐inflates, however, to the occupied container‐like species on standing in solution (see scheme).

Fully Collapsed Imploded Cryptophanes in Solution and in the Solid State

“…The out ‐ saddle conformation of imploded cryptophanes was first unequivocally demonstrated by Holman and co‐workers with a crystal structure of a m ‐xylyl‐linked anti cryptophane, and there has been one further crystal structure of an imploded cryptophane with triallyl decoration from Dmochowski and co‐workers . With the benefit of these well‐characterised examples of out ‐ saddle cryptophanes, early reports by Collet of out ‐ out cryptophanes with highly flexible O(CH 2 ) n O ( n =6–10) linkers being in equilibrium with their out‐in CC conformations (Scheme ) were subsequently reinterpreted as the out ‐ saddle forms, based on signature chemical shifts . Furthermore, gas‐phase computational studies of the imploded form of cryptophane‐E with (OCH 2 CH 2 O) bridges between CTG units concludes the saddle‐out conformer is of relatively similar energy to out‐out forms, and even being slightly lower in energy than guest‐free cryptophane .…”

“…The typical structure has a crown‐crown (CC) out‐out conformation in which the two upper rims the CTBs face one another, Scheme . There are a handful of reported examples of out – saddle conformation, which is observed in those cases in which one crown has undergone pseudo‐rotation to the twisted saddle form giving a partially “imploded” crown‐saddle (CS) structure, Scheme . The out ‐ saddle conformation of imploded cryptophanes was first unequivocally demonstrated by Holman and co‐workers with a crystal structure of a m ‐xylyl‐linked anti cryptophane, and there has been one further crystal structure of an imploded cryptophane with triallyl decoration from Dmochowski and co‐workers .…”

“…There are a handful of reported examples of out – saddle conformation, which is observed in those cases in which one crown has undergone pseudo‐rotation to the twisted saddle form giving a partially “imploded” crown‐saddle (CS) structure, Scheme . The out ‐ saddle conformation of imploded cryptophanes was first unequivocally demonstrated by Holman and co‐workers with a crystal structure of a m ‐xylyl‐linked anti cryptophane, and there has been one further crystal structure of an imploded cryptophane with triallyl decoration from Dmochowski and co‐workers . With the benefit of these well‐characterised examples of out ‐ saddle cryptophanes, early reports by Collet of out ‐ out cryptophanes with highly flexible O(CH 2 ) n O ( n =6–10) linkers being in equilibrium with their out‐in CC conformations (Scheme ) were subsequently reinterpreted as the out ‐ saddle forms, based on signature chemical shifts .…”

Cryptophanes and Their Complexes—Present and Future

“…31 Host anti-11 encapsulated one THF molecule, which filled the molecular cavity. Under heating at temperatures above 100°C, the complex lost THF to give free anti-11 ( Figure 3).…”

Organometallic cavitands: Cation–π interactions and anion binding via π-metallation

“…In the solid state the calixarenes exhibit an extensive inclusion chemistry with interesting gas and liquid sorption properties [18][19][20][21][22], although binding to neutral guests in solution by the unmodified hosts is weak. Related to the calixarenes is cyclotriveratrylene (CTV), a rigid, shallow bowl-shaped macrocycle with electronrich aromatic rings that is also well known both as a host in its ଝ Based on a keynote lecture presented at the 37th International Conference on Coordination Chemistry, 13 own right [23,24] and as a component in cavitands and cryptophanes [23,25,26]. In the solid state the compound stacks the base of each host in the cavity of an adjacent molecule.…”