Diphosphaallyl Complexes

Diphosphaallyl complexes are known in which all three atoms of the P-C-P group are believed to be bonded to the metal atom. 

---

The reaction of anionic transition metal complexes (M = Mo, W, Co) with monohalogenated diphosphiranes (2f-g) occurs upon heating and leads to the o- or 7t-diphosphaallyl complexes as a result of preferential P—P bond rupture, depending on the reaction conditions, the nature of the intracyclic carbon substituents, and the transition metal complexes (Scheme 10) <93PS(76)4i, 93JOM(453)77>. rc-Donor substituents (R3 = Ph) promote the >/3-form, whereas u-donor (R3 = Me) afford the t] -complex. 

The complexes are thermally labile as shown by variable-temperature NMR spectroscopy. Upon heating in toluene at reflux for 3 h, the u-diphosphaallyl cobalt complex is irreversibly transformed into the 7r-allylic complex. This isomerization upon heating constitutes the first example of such interconversion in the diphosphaallyl systems. The synthesis of a- or rc-diphosphaallyl complexes can also be realized from the photochemical isomers of diphosphiranes, the 1,3-diphosphapropenes. In this case, the reaction occurs more readily under milder conditions than above, and the same diphosphaallyl complexes were obtained in 70-90% yield with the same selectivity as their parent diphosphiranes <93JOM(453)77>. 

---