Emergence of Hemicryptophanes: From Synthesis to Applications for Recognition, Molecular Machines, and Supramolecular Catalysis

Abstract

In the wide area of host-guest chemistry, hemicryptophanes, combining a cyclotribenzylene (or cyclotriveratrylene CTV) unit with another different C-symmetrical moiety, appears as a recent family of molecular cages. The synthesis and recognition properties of the first hemicryptophane were reported in 1982 by Collet and Lehn, but the very little attention received by this class of host compounds in the 20 years following this first promising result can account for their apparent novelty. Indeed, in the last 10 years hemicryptophanes have aroused growing interest, and new aspects have been developed. Thanks to the rigid shaping unit of the north part (CTV) and also the variable and easily functionalized south moiety, hemicryptophanes are revealed to be inherently chiral ditopic host compounds, able to encapsulate various guests, including charged and neutral species. They also enter the field of stimuli-responsive supramolecular systems exhibiting controlled functions. Moreover, endohedral functionalization of their inner cavity leads to supramolecular catalysts. The confinement of the catalytic center affords nanoreactors with improved catalytic activities or selectivities when compared to model systems without a cavity. The current trend shows that reactions in the confined space of synthetic hosts, mimicking enzyme behavior, will expand rapidly in the near future.

Synthesis, resolution, and chiroptical properties of hemicryptophane cage controlling the chirality of propeller arrangement of a C3 triamide unit

“…In 1982, the same authors published the synthesis of a new class of chiral molecular hosts, also based on the CTV unit, and named hemicryptophanes, which associate a CTV moiety with another C 3 symmetrical unit . This class of molecular cages was found to have a wide range of applications from molecular receptors to supramolecular catalysts and molecular machines …”

Macrocycle‐Enabled Counteranion Trapping for Improved Catalytic Efficiency

“…Among which various macrocyclic compounds have been widely used and played a vital role. On one hand, many cavity‐containing macrocycle and cage compounds including cyclodextrin, cucurbiturils, cavitands, calixarenes and hemicryptophanes can serve as a catalysis vessel to accommodate reaction substrates within their confined cavities and facilitate otherwise unfavored transformations in bulk solutions. On the other hand, the macrocycle‐enabled high binding affinity towards certain guests can be utilized to mediate a catalysis process through tightly binding an “indirect” catalytic species, for example, counterions.…”

Self-Assembly in Polyoxometalate and Metal Coordination-Based Systems: Synthetic Approaches and Developments

“…Nitschke et al Supramolecular coordination complexes have attracted the attention of various research [101,102] groups due to their applications in catalysis [103], recognition and separation [104], stabilization of sensitive species [105], etc. The ability of incorporating different functional groups to coordination cages during the self-assembly process renders the final compounds excellent candidates for rational design of supramolecular nanoreactors [106]. Very often, the guest molecules are encapsulated centrally due to their solvophobicity and size complementarity between guests and hosts.…”