OXYGEN ATOM TRANSFER FROM A PHOSPHINE OXIDE TO TUNGSTEN(II) COMPOUNDS

WCl2(PMePh2)4 (1) reacts rapidly with Ph2P(O)CH2CH2PPh2 (5, the monooxide of diphos) to give an adduct, WCl2[Ph2P(O)CH2CH2PPh2](PMePh2)2 (6). On being heated at 80-degrees-C for 8 h, 6 rearranges by transferring the phosphoryl oxygen to tungsten, with the formation of tungsten-oxo complexes W(O)Cl2(diphos)(PMePh2) (7) and W(O)Cl2(PMePh2)3 (2), as well as WCl2(diphos)(PMePh2)2 (8). This is the first example of oxygen atom transfer from a phosphine oxide to a metal center, a remarkable reaction because of the strength of the P-O bond (roughly 130 kcal/mol). The presence of an oxygen atom transfer step in this reaction has been confirmed by oxygen-18-labeling studies. WCl2(PMe3)4 (9) also deoxygenates 5, forming similar tungsten-oxo complexes, but in this case an intermediate is not observed. Nonchelating phosphine oxides are unreactive with 1 and 9, indicating that the chelating nature of 5 is needed to assist the initial coordination of the phosphoryl oxygen. The kinetic barriers to deoxygenation of phosphine oxides lie both in the initial coordination of the phosphine oxide and in the actual oxygen atom transfer step. Allyl- and vinylphosphine oxides also react with 1, but oxygen atom transfer from these substrates has not been observed. An unusual tungsten-oxo complex with a chelating allyldiphenylphosphine oxide, W(O)Cl2[CH2=CHCH2P(O)Ph2]PMePh2 (13) has been isolated and its X-ray crystal structure determined. Crystal data for 13: a = 9.2547 (9) angstrom, b = 16.738 (2) angstrom, c = 18.023 (2) angstrom, beta = 100.696 (9)-degrees, monoclinic, P2(1)/c, Z = 4.