Pentaphenylcyclopentaphosphane [(PhP)5] reacts with alkyl Grignard reagents at room temp. to produce synthetically useful pro-P-stereogenic magnesium phosphides 1.  Schlenk equil. of 1 can be manipulated with excess alkyl Grignard or satn. of THF solns. with magnesium dihalide.  The latter promotes the formation of diphosphinomagnesium 2, which undergoes reductive elimination of magnesium to form 1,2-diphenyl-1,2-dialkyl-diphosphine 3 in high yield.  Subsequent addn. of alkyl Grignard reagents to solns. of 3 at reflux gives P-stereogenic tertiary phosphines 4, along with regenerated 1.