Borenium and boronium ions of 5,6-dihydro-dibenzo[c,e] [1,2]azaborinine and the reaction with non-nucleophilic base: trapping of a dimer and a trimer of BN-phenanthryne by 4,4'-di-tert-butyl-2,2'-bipyridine.

6-Chloro-5,6-dihydro-dibenzo[c,e][1,2]azaborinine (1) reacts with pyridine derivatives to borenium or boronium ions. The boronium ion obtained from reaction with an excess of pyridine could be characterized structurally and transforms into the borenium ion in solution. The reaction of 1 with 2,2'-bipyridine (a) and derivatives (b: 6,6'-dimethyl; c: 4,4'-di-tert-butyl) results in spirocyclic boronium ions 8a-c of which 8b could be characterized by X-ray crystallography. Despite the chelate effect, the spirocyclic boronium ions readily undergo hydrolysis or alcoholysis. Treatment of the spirocyclic boronium ion 8c with potassium hexamethyl disilazide (KHMDS) results in neutral products that are monomers, dimers, or trimers of dibenzo[c,e] [1,2]azaborinine ("BN-phenanthryne") trapped with 4,4'-di-tert-butyl-2,2'-bipyridine by formation of B-C, B-N, or dative B-N bonds, indicative of deprotonation of NH and CH bonds of the boronium ion by KHMDS. [ABSTRACT FROM AUTHOR]