Evidence for Terminal Phosphinidene Oxide Complexes in O,P,C-Cage Complex Formation: Rearrangement of Oxaphosphirane Complexes

A comparative study on the stereoselective synthesis of O,P,C-cage complexes is described using oxaphosphirane M­(CO)5 complexes (M = Cr, Mo) and acetaldehyde or benzaldehyde. All products were unambiguously characterized by elemental analysis, multinuclear NMR, IR, MS, and single-crystal X-ray diffraction studies. DFT calculations provide evidence for initial C–O bond cleavage of the oxaphosphirane ring, most likely assisted by the selective bond weakening effect arising upon preliminary van der Waals complex formation. Subsequent P → C rearrangement of the Cp* group affords a phosphinidene oxide complex as key intermediate, which is responsible for the highly diastereoselective anchoring of the carbonyl compound.