Contribution to the Chemistry of Boron, 136 [1] A Reinvestigation of the Existence of l,3,2-Dioxaborinium(l-|-) Cations

The chemistry of boron cations was a field long neglected [2]. Meanwhile, many cations containing tetracoordinated boron have been reported [3] and their chemistry has been explored. In addition there exists scattered information relating to tri[4-8] and dicoordinated [9, 10] boron cations. Unlike carbenium ion chemistry their role in boron chemistry is not yet well understood. This situation, however, will quickly change as their chemical behaviour is being studied. Having evaluated some governing factors relating to the stability of dicoordinated cations of boron [9] we became interested in those of coordination number 3 because their stability should also depend on mesomeric effects. Such effects could prevail in tricoordinated l,3,2-dioxa-borinium(l + ) salts 1 which were isolated as Perchlorates and hexachloroantimonates [5-7]. One important argument for the presence of a tricoordinated boron atom in these compounds was an n B NMR signal at ~ 26 ppm which is typical for a CBO2 structural unit [11].