Synthesis and structures of two new types of boronium salts

Transamination of di(pyrid-2-yl)amine (1) with B(NMe2)(3) leads to the isomeric heterocyclic bis(dimethylamino)boryl compound 4 and not to bis(dimethylamino)di(pyrid-2-yl)aminoborane (2). B(NMe2)3 reacts with aniline (1:2 ratio) to yield a 1:1 mixture of B(NHPh)(3) and (Me2N)(2)BNHPh. Transamination of this mixture with 1 yields the anilinodimethylamino analogue of 4 (compound 7). Compound 4 reacts with CHCl3 to generate the boronium salt 5 by the abstraction of HCl from CHCl3 and addition of HCl to one of the dimethylamino groups. Compound 5 crystallizes with 4 molecules of CHCl3. Compound 4 is attacked by AlCl3 in toluene to give a mixture of unidentified products from which the tetrachloroaluminate of a new type of spirocyclic diboronium cation, 8, was isolated and characterized by X-ray crystallography. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)