Solution-state 15N NMR and solid-state single-crystal XRD study of heterosubstituted diazaboroles and borinines prepared via an effective and simple microwave-assisted solvent-free synthesis

A quick and simple, solvent-free synthesis of nitrogen-basedboroles and borinines derived from 1,2-diaminobenzene and 1,8-diaminonaphthalene is reported and compared with the traditional synthetic method. Characterization by 15N NMR spectroscopy of 12 compounds and single crystal X-Ray diffraction of 4 compounds provides supporting evidence for donation of electron density, from the N-atom to the vacant pz orbital of the B-atom. Furthermore comparison of the hitherto unreported crystal structure of 2-(4-Methylphenyl)-naptho[1,8-de][1,3,2]diazaborinine with similar compounds made in these laboratories reveals that solid-state packing and the dihedral angle between naphthyl and phenyl rings is determined by competing inter- and intra-molecular forces.

Graphical abstractThe microwave-assisted solid-state and traditional solution-based methods for the preparation of twelve nitrogen-based boroles are compared. Solution-state 15N NMR and solid-state structures are discussed with regard to back-donation of electron density and solid-state packing.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of diamonoboranes using a solvent-free microwave-assisted system. ► 15N NMR evidence for electron density back-donation from nitrogen to boron atoms. ► Solid state structure of a naphtho[1,8-de][1,3,2]diazaborinane.