A cationic mononuclear and a neutral trinuclear boron compound derived from boric acid and N2O2-type ligands of the Salan class

Four different ligands of the Salan class have been prepared and reacted with boric acid. Reaction of saleanH4 (saleanH4 = N,N′-bis(o-hydroxybenzyl)-1,2-diaminoethane) with three equivalents of boric acid gave a neutral trinuclear boron complex containing two four-coordinate and one three-coordinate boron atom involved in a system of four heterocyclic rings of the composition {C3BNO}, {C2B2N2O} and {B3O3}. The salceanH4 ligand (salceanH4 = N,N′-bis(o-hydroxybenzyl)-trans-1,2-diaminocyclohexane) gave a so far unknown mononuclear boronium complex of the general formula [(RO)2B(NR′R′′)2]+. Both compounds might have applications, the trinuclear species as Lewis acid catalyst and the borocation as positively charged counterion for voluminous anions. With salpanH4 (salpanH4 = N,N′-bis(o-hydroxybenzyl)-1,3-diaminopropane) and salophanH4 (salophanH4 = N,N′-bis(o-hydroxybenzyl)-1,2-diaminobenzene) only unseparable product mixtures of oligo- and/or polymeric boron complexes could be obtained.

Graphical abstractA mononuclear boronium and a neutral trinuclear boron complex have been prepared by reaction of two different Salan ligands with boric acid. Both compounds might have applications, the trinuclear species as Lewis acid catalyst and the borocation as positively charged counterion for voluminous anions.Figure optionsDownload full-size imageDownload as PowerPoint slide