The deoxygenation of phosphine oxides, which are intractable wastes in laboratories and industry, is of significance to the sustainability of phosphorus chemistry.¹ However, the thermodynamic inertness of P=O bonds makes their reduction a great challenge. Previous methods in this regard relied primarily on P=O bond activation by either Lewis/Brønsted acids or stoichiometric halogenating reagents under harsh conditions. We reported a new catalytic strategy for facile and efficient deoxygenation of phosphine oxides via successive isodesmic reactions, where the thermodynamic driving force required for scission of the strong P=O bond was fulfilled by the synchronous formation of one other P=O bond in catalytic species.² This catalytic reaction avoids stoichiometric activator, and features a broad substrate scope, excellent reactivities, and mild reaction conditions. Mechanistic and thermodynamic studies revealed dual synergistic roles of the catalyst. Furthermore, we developed a phosphonium-catalyzed mono-reduction of bisphosphine dioxides to access an array of synthetically-useful BPMOs with axial, spiro, and planar chirality.³ The origin of the distinctive mono-reduction selectivity was studied experimentally and theoretically.