Two-electron Reduction of Diboryldiphosphene: Formation of Intramolecular Charge-transfer Complex of Dianionic B-=P-P=B- Species

Boryl-substituted diphosphene was reduced by treatment with an excess amount of Li to form dianionic diboryldiphos-phanediide 2. Reaction of 2 with MeI resulted in methylation at the two negatively charged phosphorus atoms. NMR spectroscopy, X-ray crystallographic analysis, and DFT calculations revealed that the coordination of DMAP to 2 induced significant p pi-p pi interactions between P and B atoms. The UV-vis spectrum of 2 center dot[DMAP](2) exhibited characteristic absorption at lambda(max) = 380 nm, which could be assigned to an intramolecular charge transfer from the pi-orbital of the B-=P-P=B- moiety to the pi*-orbital of the DMAP ligand as per TD-DFT calculations.