Azadibenzophospholes: Functional Building Blocks with Pronounced Electron-Acceptor Character

A series of azadibenzophospholes with varying location of the nitrogen center has been synthesized and comprehensively characterized. In the context of the study, suitably brominated phenylpyridine precursors were accessed via Suzuki-Miyaura cross-coupling for the first time. Despite being nonfluorescent, X-ray crystallographic studies of two azadibenzophosphole oxides revealed planar conjugated scaffolds with high degree of pi-conjugation. The P-oxidized species were found to show desirable reversible reduction features that support promising electron-accepting properties of the materials. The presence of the nitrogen as well as phosphorus centers within the scaffold allowed for further functionalization with transition metals, as well as methyl groups that result in altered absorption and redox features for the materials. Subsequent bromination of the scaffold selectively occurred at the exocydic P-phenyl group, as confirmed via X-ray crystallography. This halogenation allowed for further modification of the system via catalytic cross-coupling with pyridine.