Aromatic organoboron compounds

Borazarophenanthrene was the first representative of a new class of heteroaromatic compounds containing boron atoms in six-membered aromatic rings.4 These compounds are of a different order of stability from previously known types of organoboron compounds, being chemically similar to normal aromatics, and their discovery has opened up a new field of aromatic chemistry. The procedure indicated here has been used to prepare a large number of related aromatic systems. 

Aromatic chloro compounds. Photolysis of aromatic iodides has been used for synthesis of triphenyls, phenanthrenes, and organophosphorus and organoboron compounds.1 If the photolysis is carried out in carbon tetrachloride with 3000-A light2 for about five hours, the corresponding chloro compound is obtained in 50-95% yield.3... 

Kakiuchi F, Usui M, Ueno S, Chatani N, Murai S (2004) Ruthenium-catalyzed functionalization of aryl carbon-oxygen bonds in aromatic ethers with organoboron compounds. 1 Am Chem Soc 126 2706-2707... 

Two further methods of preparing organoboron compounds have been the subject of fairly recent detailed study, namely, reaction of boron halides with hydrocarbons and addition of boron hydrides to olefins. For instance, arylboron dihalides are formed when boron trihalides are heated with aromatic hydrocarbons, aluminum chloride, and aluminum powder,217 and phenyl-boron dibromide has been prepared analogously.218 Further, boron halides such as diboron tetrachloride and tetrafluoride add to olefins, yielding bis-(dichloroboryl) and bis(difluoroboryl) compounds 219... 

Carbanions can also function as electron-donors to organoboron compounds the products are complex ions. Thus reaction of trimethylboron with methyl-lithium in ethereal solution affords lithium tetramethylborate. The aromatic analog, sodium tetraphenylborate Na[B(C6H5)4], is an important reagent for gravimetric determination of potassium and a number of other ions, because lithium and sodium tetraphenylborate are soluble in water whereas the potassium, rubidium, cesium, and ammonium salts are almost completely insoluble therein. 

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