Phenylene-1,4-diboronic acid

The Stille coupling was also employed successfully to prepare covalently bound DNA base-pairs. 1,4-, and l,3-bis(stannyl)benzenes were used to connect purine units covalently through a phenylene linker. The reactions gave the desired products in mediocre yield, along the by-products of destannylation and mono-coupling (8.21.), The extension of the procedure to benzene-1,4-diboronic acid met with limited success.29... 

Schliiter et alJ65,66 have recently used rod-shaped polymers1673 such as poly(p-phe-nylene)s and poly([l.l.l]propellane)s as cores for the attachment of convergently generated dendrons. These new branched macromolecules possess a rigid backbone wrapped with structural wedges, which become increasingly more dense toward the outer cylindrical surface. The Pd-catalyzed copolymerization of dibromobiphenyl derivatives with the Frechet-type ethereal dendrons with a substituted aryl diboronic acid afforded the dendritic coated poly(p-phenylene) rod. 

Weber and Thomas [270] prepared rigid poly(p-phenylene)-type polymeric networks by reacting tetrafunctional building blocks of tetrabrominated 9,9 -spirobifluorene with benzene-1,4-diboronic acid or 4,4 -biphenyldiboronic acid in a mixed organic solvent. Here, the contorted unit of spirobifluorene forces the four polyphenylene chains to grow in four different directions. 

Readily soluble poly(2,9-o-phenanthroline-(2, 5 -dihexyl)-4,4"-p-ter-phenylene)s with a degree of polymerization up to 39 have been prepared via a Pd-catalyzed polycondensation reaction of 2,9-bis-(p-bromophenyl)-o-phenanthroline and 2,5-dihexylbenzene-l,4-diboronic acid [50]. Some cyclic oligomers could be separated from the polymer. Diamagnetic transition metal complexes of well-defined constitution as shown in 26 were obtained with Cu(I) and Ag(I) without branching and cross-linking. 

Several years later, Reynolds and co-workers [179] extended this work to prepare another sulfonated poly(p-phenylene) using the same approach by replacing 1,4-diboronic acid with 4,4 -biphenyl diboronic ester ... 

Solid polymer electrolytes have been actively pursued as a major contribution to the development of high-energy density batteries, particularly lithium secondary batteries. The poly(p-phenylene)s substituted with oligo(oxymethylene) side chains and blends of these novel polymers with lithium salts are achieved by biaryl coupling of benzene-1,4-diboronic acids (Fig. 4). ° OctapoIy(p-phenylene) functions as the artificial ion channel which specially recognizes (bio)membranes by their thickness (Fig. 5). ... 

Taking advantage of the more traditional cyclic ester formation between boronic acids and 1,2- and 1,3-diols can also lead to macrocyclic structures. It has been shown by NMR, FTIR, and size exclusion chromatography (SEC) that reaction between phenylene-l,3-diboronic acid and pentaerythritol principally produces 6 6, hexameric cycles (Fig. 16a)." As before, the crude reaction mixture was a dynamic mixture of cyclic and oligomeric products, but the... 

FIGURE 16. (a) When phenylene-l,3-diboronic acid was coupled with the bis-l,3-diol, pentaerythritol, traditional cyclic boronate ester formation resulted in macrocyclic structures, (b) The bis-l,2-diol 1,2,4,5-tetrahydroxybenzene forms similar structures. 

FIGURE 17. Solvent can form templates of (a) 2 2 and (b) 3 3 cyclic adducts from phenylene-l,4-diboronic acid with a racemic bis-diol. 

The earliest recorded poly(boronate)s were tri-coordinate systems based on phenylene-l,4-diboronic acid. Some of the first materials were not in fact esters... 

Then, the Pd-catalyzed coupling reaction of diboronic acids 29 or 32 with dibromo compounds 28, 30, or 31 gave telomer copolymer 33 with defined blocks of one to six nonsubstituted phenylene units (Scheme 13). A vapor pressure osmometry measurement of 33 (y = 2) gave = 21,000. Thus,... 

The synthesis of poly(p-phenylene) via the homocoupling of p-hro-mophenylboronic acids was first reported by the Max Planck Institut. After this discovery, various new poly(p-phenylenes) were synthesized. A rigid-rod poIy(p-phenylene) was prepared by cross-coupling a biphenyl diboronic ester and a dibromide in aqueous DMF in the presence of a water soluble palladium catalyst (Eq. 78). The... 

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