In this paper, we report the first metal-catalyzed, highly selective, and efficient mono- oxidation of bidentate phosphines to bis-phosphine monoxides (BPMOs) of the general formula R2P-(O)-Y-PR2, where Y is a divalent bridging group. A number of BPMOs have proven to be valuable soft/hard ligands for inorganic/organometallic synthesis1 and especially catalysis with transition metals. 2-5 The use of BPMOs for the hydroformylation2 ...