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.