Dynamic Reactivity: Reversible Reaction of a Phosphinine–Borane Adduct With Water and Double Hydrophosphination

An unprecedented reversible addition of water to a 3,5-bis(SiMe3)phosphinine→B(C6F5)3 was observed, revealing the formation of novel 1,2- and 1,4-dihydrophosphinine oxide-borane adducts. Experimental results, supported by DFT calculations, unveiled two plausible reaction pathways, enabled by the liberation of phosphinine upon water coordination to the borane. On the basis of our results, the water addition can be reversed under basic conditions, regenerating the aromatic phosphorus heterocycle. Furthermore, treating the mixture of the dihydrophosphinine oxides with the sterically demanding and weak base tris(tert-butyl)phosphine induced a unique double hydrophosphination, yielding a bicyclic diphosphine oxide. These findings highlight a new mode of small molecule activation and dynamic structural interconversion by aromatic phosphorus heterocycles.