Reaction pathways for the formation of zirconocene phosphinidene complex Cp 2 Zr(PR 3 )PR from Cp 2 ZrCl 2 and LiH and LiPRH and its reactivity to 1,2-dichloroethane are explored with density functional theory using model structures that are devoid of substituents. After the initial Cp 2 Zr(Cl)PH 2 is generated with LiPH 2 reaction with LiH is likely to eliminate HCl in a single step to give directly the 16-electron complex Cp 2 ZrPH, which is stabilized by the PH 3 phosphine ligand. The intermediate formation of a phosphine hydride complex, Cp 2 Zr(H)PH 2 resulting from hydride substitution, is unlikely both on the basis of unfavorable reaction energies and calculated 31 P NMR chemical shifts that indicate that such a species cannot have been observed experimentally. It is likely that a diphosphine complex, Cp 2 Zr(PH 2 ) 2 , results on using an excess of the lithium phosphide, which on H-transfer gives directly the phosphine-stabilized phosphinidene complex. The reactivity of this species is dominated by the release of its stabilizing phosphine ligand to give a highly reactive 16-electron phosphinidene complex, Cp 2 ZrPH, which reacts with 1,2-dichloroethane after coordination to one of the chlorine atoms in two asynchronous metathesis steps to the three-membered phosphirane ring. In this process, ZrCl 2 is reformed enabling its recycling to regenerate the phosphinidene complex. This study highlights the special reactivity of the 16-electron Cp 2 ZrPH and suggests that related complexes may be generated similarly, thereby expanding the synthetic potential of these nucleophilic reagents.