Linked Boronate Assemblies

Beyond the coordinative interactions described, boronate ester formation by itself has been shown to facilitate the generation of macromolecular and polymeric structures. Taking advantage of the covalent yet reversible nature of boronate ester formation has allowed for the formation of thermodynamically stable assemblies. Of course, simple monoesters, diesters, and triesters have been readily synthesized and characterized. Numerous reports have taken advantage of the formation of cyclic diesters as a means to define selectivity for molecular sensors, but these small cycles will not be discussed here. Attempts to synthesize and characterize macrocyclic, polymeric and extended covalently 

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Cyclic voltammograms of the COx/Cyt.c electrode corresponding to the bioelectrocatalyzed reduction of 02 (i), and to the reference system, where 02 is excluded (ii). (c) Assembly of an integrated LDH electrode for the bioelectrocatalyzed oxidation of lactate by the surface cross-linking of an affinity complex formed between LDH and different structures of a boronate-linked PQQ-NAD monolayer. Parts (a) and (b) Reproduced from Ref. 27 by permission of the Royal Society of Chemistry (RSC). Part (c) Reproduced with permission from Ref. 25. Copyright 2002 American Chemical Society. 

Growing from simple polymeric assemblies, more complex structures arise from the interactions between polyvalent boronic acids interacting with poly-functional diols. These products may be dynamic, highly cross-linked polymer networks, analogous to slime. Alternatively, these assemblies have taken the form of highly ordered frameworks with persistent pores. Regardless of the degree of order inherent in these systems, the key assembly motif still relies on boronate ester formation. 

One of the unique architectural motifs that truly relies on the covalent yet reversible nature of boronate ester formation is the creation of complex hierarchical structures referred to as COFs. If boronate ester formation can be used to obtain discrete macrocyclic structures, it is then reasonable to expect that linked macrocyclic networks may be generated. These networks assemble... 

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