4,4 -biphenyldiboronic acid

In contrast, reaction of ligand 72 with 4,4 -biphenyldiboronic acid has been successful and diboronate 73 is obtained in yields of 33%. This complex acts as a receptor for the paraquat dication forming a 1 1 complex with an association constant of 320 in acetone. The intermolecular forces responsible for the complexation are ion-dipole stabilization between the dative N B dipoles and the two cationic centers in paraquat, attractive tz-tz interactions between... 

Fig. 19. Transformation of diboronates 69-71 to macrocyclic derivatives was not possible, however, with 4,4 -biphenyldiboronic acid 72 compound 73 is formed...

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. 

Incorporation of this coordinative amine ligand within the cycle structure is an alternative approach for generating stable macrocycles. In this regard, alkyl bridged bis(2-hydroxyphenylmethyl) amines have been reacted with 4,4 -biphenyldiboronic acid (Fig. 19a). Esterification proceeds with concomitant coordination of the amine to the resulting ester. The paraquat dication is complexed by this assembly in a 1 1 manner (Fig. 19b) through ionic interactions (anionic boronate with pyridyl cation), attractive n-n interactions (between biphenyl components) and C —H —O hydrogen bonds (paraquat... 

---