Boron, terphenyl derivatives

Terphenyl derivatives of boron were originally synthesized with the object of preparing compounds with B-B triple bonds. It was thought that these aryl ligands would be effective in the stabilization of triple bonds in a similar manner to their success in the stabilization of double bonds. For example, a B-B triple-bonded boron analogue of a substituted acetylene might be accessible by reduction of an ArBX2 or l,2-dimethoxydiborane(4) species as shown by Eq. (3). 

Based upon this principle, aryl Pd species like 34 can also terminate in a transmetallation with boronic acids (i.e., in a Suzuki coupling) where the biphenyl 35 was obtained in 90% yield (Scheme 11) and the terphenyl derivative 36 was isolated in 93% yield (Scheme 12) [69]. 

The second synthetic route consists of the coupling of hexa(4-iodophenyl)ben-zene (34) with an alkylated oligophenylboronic acid to produce a hexa(oligo-phenyl)benzene by extending the aromatic chain [52]. This route is illustrated by the reaction of hexa(4-iodophenyl)benzene (34) with an alkylated terphenyl boronic acid with formation of the hexa(quaterphenyl)benzene derivative 33. Once again, the aliphatic substituents serve to guarantee sufficient solubility. 

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