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Od oddziaływań supramolekularnych do molekularnych

Brandt K., Siwy M., Lach D.

Wiadomości Chemiczne

2000

[Z] 54, 5-6

389-434

The review is focused on the problems of supramolecular assistance to molecular synthesis which means the employment of supramolecular interactions to control the chemical synthesis, i.e. to guide the regio- and/or stereoselective formation of covalent and/or mechanic bonds. Such an approach results from the tendency to mimic processes occurring in natural biological systems. The special attention is focused on the recent achievements in this field, i.e. on the design of so-called intelligent substrates, which contain in their structure the requisite stereoelectronic information needed to self-assemble spontaneously into a supramolecular intermediate, which converts further into a desired final product after the formation of one or more covalent bonds. Among the unusual structures obtained using this synthetic paradigm, mechanically interlocked molecular compounds, i.e. rotaxanes, catenanes and their supramolecular precursors: psedorotaxanes, are described in more detail, as they display features of bistable chemical switches, and therefore evolve currently a great scientific interest due to their prospective applications in nanotechnologies. Several examples have been given of supramolecular assistance to other complex chemical syntheses, in particular of organic compounds, organo(cyclophosphazenes) and oligonucleotides, enabling to perform them quickly and selectively from polyfunctional reagents, without the necessity to use any protecting groups. It has been emphasized that supramolecular interactions play a special role in guiding so-called self-replication processes of the molecules containing in their structure both reactive groups, able to undergo co-condensation, and complementary to those contained in the substrates supramolecular synthons (motifs), capable to form appropriately oriented ternary complexes with these substrates, in which the functional groups are in favourable position to interact towards the desired product. An influence of spontaneous self-assembly of the substrates, preceding their linking via covalent bond(s), on regio- and stereochemistry of the occurring processes has been discussed, with the special attention being paid to the role of so-called templates (previously named matrices), determining the orientation of the substrates due to the stabilization of particular transition states. Several types of templates have been discussed: complementary hydrogen bonding, metal cations (alkali metal, transition metal), p-donor-p-acceptor interactions and various combinations of the above mentioned; the examples of the respective template-driven syntheses have been quoted. The reactions of functional macrocyclic ligands, assisted by supramolecular interactions with the nucleophilic ion-paired co-reagents, have been only briefly mentioned and limited to the examples of the exchange reactions of benzo-crowns with substituents in aromatic rings, and of chlorocyclophosphazene-crowns.