The transformation pathway of tetrahedral P4 to the corresponding Pn ligands has been studied by the three-component-reaction are found to depend on the electron number of the complex fragments used. In the case of complexes forming fragments with an even number of valence electrons, a stepwise P-P bond cleavage is observed with a bicyclotetraphosphine intermediate to give a cyclo-P4 containing product. Complexes with an odd number of valence electrons cause a P1/P3 fragmentation. A possible product of this reaction is a phosphido complex of the type [LnM≡P→M'(CO)5] (M' = Cr, W), which is self-stabilised by dimerisation. The phosphido complex [(tBuO)3W≡P→M(CO)5] (M = Cr, W) is formed via the reaction of W2(OtBu)6 with RC≡P in the presence of the Lewis acids [M(CO)5THF].