The vinylidene phosphine (Pr(n)(2)P)(2)C=CH(2) (1) undergoes Schlenk dimerisation on treatment with an excess of any of the alkali metals Li, Na or K to give the butane-1,4-diide complexes [(L)M{(Pr(n)(2)P)(2)CCH(2)}](2)[(L)M =(THF)(2)Li (6), (THF)(3)Na (7b), (DME)(2)K (8b)], after recrystallisation. Whereas the reaction between the analogous phenyl derivative (Ph(2)P)(2)C=CH(2) and K results in cleavage of a P-C bond, 1 reacts smoothly with K to give 8, with no evidence for P-C cleavage. Compound 6 is an excellent ligand transfer reagent: metathesis reactions between either 6 or its phenyl analogue [(THF)(2)Li{(Ph(2)P)(2)CCH(2)}](2) (2) and two equivalents of Cp(2)ZrCl(2) in THF give the corresponding dinuclear zirconocene derivatives [Cp(2)Zr(Cl){(R(2)P)(2)CCH(2)}](2) in good yields [R = Ph (11), Pr(n)(12)]. Compounds 6, 7b, 8b, 11 and 12 have been characterised by multi-element NMR spectroscopy and, where possible, by elemental analysis; compounds 6, 7b, 11 and 12 have additionally been characterised by X-ray crystallography.