Catalytic Hydrophosphination of Allenes Using an Iron(II) -Diketiminate Complex

A rare study into the catalytic hydrophosphination of allenes is reported. Employing an Fe(II) ss-diketiminate pre-catalyst, the reaction of HPPh2 proceeds with a range of aryl- and alkylallenes. For arylallenes the E-vinyl product forms as the major species, while the 1,1-disubstituted alkene is formed in a larger ratio than the Z-vinyl product (e.g., 6:3:1 as E/1,1/Z). The use of H2PPh results in good yields of the 1,1-disubstituted alkene, where the resultant secondary phosphine product does not undergo further reaction. We postulate a catalytic cycle based on spectroscopic data. Employing an [Fe(salen)](2)-mu-oxo pre-catalyst leads to phosphine dehydrocoupling rather than hydrophosphination.