Inorganic Ferrocene Analogue [Fe(P4)2]2

Abstract

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 P₄ phosphorus except for the generation of [Ti(η⁵-P₅)₂]^2-. Herein, we report a facile one-step method for the synthesis of the homoleptic iron complex [Fe(P₄)₂]^2- by the Zintl-phase-type precursor KP. ³¹P NMR analyses indicate that upon dissolving the KP phase in ethylenediamine P₄^2- 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(P₄)₂]^2-. Both the Fe^II and the Fe^III precursors can oxidize P₄^2- to give a concomitant product [(P₇)Fe(P₄)]^3-, which can be partially inhibited by the addition of potassium to produce relatively pure crystalline [K(2,2,2-crypt)]₂[Fe(P₄)₂].