Inorganic Ferrocene Analogue [Fe(P 4 ) 2 ] 2 .

Inorganic metallocene derivatives containing only cyclo-P n ligands have been targeted for more than 20 years, but their syntheses have never been achieved by pursuing the conventional route of using P 4 phosphorus except for the generation of [Ti(η 5 -P 5 ) 2 ] 2- . Herein, we report a facile one-step method for the synthesis of the homoleptic iron complex [Fe(P 4 ) 2 ] 2- by the Zintl-phase-type precursor KP. 31 P NMR analyses indicate that upon dissolving the KP phase in ethylenediamine P 4 2- was generated only in the presence of 2,2,2-crypt. The amounts of cation-sequestering agents, the type of iron precursor, and their consuming ratio have a decisive impact on the yield of [Fe(P 4 ) 2 ] 2- . Both the Fe II and the Fe III precursors can oxidize P 4 2- to give a concomitant product [(P 7 )Fe(P 4 )] 3- , which can be partially inhibited by the addition of potassium to produce relatively pure crystalline [K(2,2,2-crypt)] 2 [Fe(P 4 ) 2 ].