Competing ring cleavage of transient O-protonated oxaphosphirane complexes: 1,3-oxaphospholane and η2-Wittig ylide complex formation.

O-Protonation and ring cleavage of oxaphosphirane complexes 1a,b enabled the synthesis of novel compounds such as the bicyclic 1,3-oxaphospholane complex 5 and the η(2)-Wittig ylide complex 7, which demonstrate the emerging chemistry of this new reactive intermediate. Whereas P-O bond cleavage occurred, in the first case, thus revealing the superior ability of the P-bonded Cp* group to stabilize cationic charge, in the second case competing C-O and P-O bond cleavages occurred, thus leading to a mixture of complexes 3, 4 and 7.