Diborons

C, b.p. 91 C, and has very similar properties to boron chloride but is a stronger Lewis acid. Diboron tetrabromide BjBr, is also known. 

Polymerization by G—G Goupling. An aromatic carbon—carbon coupling reaction has been employed for the synthesis of rigid rod-like polyimides from imide-containing dibromo compounds and aromatic diboronic acids ia the presence of palladium catalyst, Pd[P(CgH )2]4 (79,80). 

Boric Oxide. Boric oxide, formula wt 69.62, is the only commercially important oxide. It is also known as diboron trioxide, boric... 

Diboron tetrafloutide [13965-73-6] iit)oron tetrachloride [13701 -67-2] diboron tetrabromide [14355-29-4] 2 %... 

Porphyrin-based diboronic acids as artificial receptors for saccharides 98YGK831. 

In a classical multi-step route the critical point is to conduct (he ring closure quantitatively and regioseleclively. In the synthesis of I.PPP, the precursor polymer 13 is initially prepared in an aryl-aryl coupling from an aromatic diboronic acid and an aromatic dibromoketone. 

Write the formulas of (a) cobalt(II) chloride hexahydrate (b) diboron trisulfide. STRATEGY... 

A different approach to the preparation of boron macrocycles can be made by using diboronates 69-71 for the construction of the macrocyclic derivatives... 

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...

Finally, a huge number of different boronic and diboronic acids has been designed with the aim to use them as molecular receptors for saccharide... 

Scheme 1. Formation of a macrocyclic complex between a diboronic acid and a saccharide...

Competitive binding studies have shown that 164 and 166 are suitable for the detection of glucose at physiological levels [253-255]. Diboronate 165 is capable of chiral recognition of monosaccharides and gave the best chiral recognition for fructose when tested with a series of different saccharides [255]. 

Compounds 167-171 outlined in Fig. 43 form another series of diboronic acids that form complexes with mono- and disaccharides. In these cases the asymmetrical immobilization of chromophoric functional groups, e.g., aromatic rings in 167-170 or Fe -complexation with the related boronate 171, can be analyzed by circular dichroism measurements [256-262]. 

Fig. 43. Compounds 167-171 form a series of diboronic acids for the complexation of saccharides with functional groups that permit analysis by circular dichroism measurements...

Reductive methods form B—B bonds from B—X bonds. For B2X4 (X = Cl, Br, I) from BXj, an electric discharge is supplemented by the presence of a metal, or metal atoms, as halide scavenger. The passage of BX3 at low pressure through a rf discharge in the presence of Hg produces the diboron tetrahalides B2X4 at 300 mg h ... 

Diboron compounds with alkylamino or alkyloxy substituents are prepared from the appropriate halogenoborane derivative using active metals " ... 

---