Investigation of the Lewis acidic behaviour of an oxygen-bridged planarized triphenylborane toward amines and the properties of their Lewis acid–base adducts

Abstract

Lewis acid behavior of an oxygen-bridged triphenylborane (1) to amines and the properties of Lewis acid–base adducts of 1 with amines have been investigated. UV-vis titration and ¹¹B NMR experiments showed the formation of Lewis acid–base adducts of 1 with pyridine, DMAP, quinuclidine, and DABCO, respectively (1·amine). X-ray crystallographic analysis revealed that the planar shape of 1 was converted to a bowl shape by the formation of 1·amine. Interestingly, 1·quinuclidine, 1₂·DABCO, and 1·DABCO exhibited dual emissions. Excitation spectra and photoluminescence decay time measurements suggest that the dual emissions were ascribed to two excited species, i.e., [1·amine]* and [1]* generated by photodissociation in the excited states.