Boronates, phenyl

In the aromatic series only one member has been obtained of the type RgB, namely, boron triphenyl. It is formed by the interaction of magnesium phenyl bromide and boron trifiuoride, an excess of Grignard reagent giving boron diphenyl fluoride and boron phenyl difiuoride at the same time. Boron triphenyl is a solid, which readily yields additive... 

Boron diphenyl bromide was first obtained as a by-product in the preparation of boron phenyl dibromide, from boron tribromide and mercury diphenyL the compound being contained in the fraction distilling above 150° C. at 20 mm. It may be more readily isolated by taking the proportions represented by the following equation —... 

Subsequent pyridine-assisted polymerization induced a solvophobic orthogonal interaction, based on phenyl-boron-phenyl jt-stacking, leading to dispersible nucleation. On aggregation, pyridine-coordinated boronate ester polymers are converted into planar structures via elimination of pyridine, because the trigonal planar state of the boronate ester is thermodynamically favoured over the pyridine-coordinated tetrahedral structure. As a result, spherical particles composed of lamellar nanostructures are produced, and their size depends on the minimization of interfacial free energy... 

T. V. Ashworth, M. J. Nolle, R. H. Reimann, and E. Singleton. Conversion of bonded cyclo-octadiene into a cyclo-octadienyl ligand and cleavage of boron-phenyl bonds of arenc-bonded tetraphenylborate anions in ruthenium(ii) systems X-ray crystal and molecular structures of [Ru(j -C H5BL3)(1-3,5,6-jj-C8Hii)] (L = Ph or F). J.C.S. Chem. Comm., 1977, 937. 

B. Novel Phenyl-Boron-Phenyl Sandwich Supramolecular... 

FIGURE 4. Electron-deficient boron atoms (yellow) in aromatic boronate esters tend to stack in supramolecular assemblies between electron-rich re-clouds, forming a phenyl-boron-phenyl sandwich. 

As demonstrated by examples, these relatively novel assemblies hold promise in a number of different venues. The simple phenyl-boron-phenyl binding motif provides a unique supramolecular assembly strategy for researchers to take advantage of. Macrocyclic assemblies have been shown to serve as host molecules for molecular recognition events. Linear polymers have shown self-repair capabihties as well as serving as wide band-gap semiconductors. And porous COFs provide stable network geometries for the inclusion of guests. 

In Chapter 6, B. M. Rombo et al. delve into the formation of boronate-linked supramolecular architectures based on boronate ester formation—for example, small molecule diesters form supramolecular self-assemblies in the solid state based on a phenyl-boron-phenyl sandwich motif in which these small oligomers link together to generate macrocycles and other polymers. The polymeric macrocyclics and linear structures demonstrate self-repair capabilities and constitute a new class of wide band-gap semiconducting materials. Through the incorporation of polyvalent boronates, covalent organic frameworks are described, which create highly crystalline, porous network materials. 

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