O,N-Chelated boron aminophenolate complexes. Crystal structure of BPh2(OC6H4(CH2NMe2)-2)

Two diphenylboron ortho-aminophenolate complexes, [BPh2(OC6H4(CH2NMe2)-2)] (2) and [BPh2(OC6H2(CH2NMe2)2-2,6-Me-4)] (6), have been prepared in a one-pot procedure approach starting from B(OMe)3. The starting material was reacted with two equivalents of phenylmagnesium bromide, followed by hydrolysis with HCl. The resulting borinic acid, BPh2(OH), was reacted with either HOC6H4(CH2NMe2)-2 or HOC6H2(CH2NMe2)2-2,6-Me-4 to give 2 or 6, respectively. An X-ray structure determination of 2 showed it to be a four-coordinate boron compound with a tetrahedral coordination geometry. The six-membered chelate ring in 2 is puckered. Variable temperature 1H-NMR analysis of 6 showed the existence of two dynamic processes in solution, i.e. one process involving flipping of the puckered chelate ring conformation (ΔG‡=41 kJ mol−1) and a second, higher energy, process (ΔG‡=65 kJ mol−1) in which exchange of coordinated and non-coordinated amine functions occurs. The exchange is (at least partly) assisted intermolecularly.