One-dimensional anionic radical chains based on M₂P₂ rings (M = Ti, Zr, Hf)

This work deals with the synthesis of metallocene-phosphorus based radical coordination polymers. The radical polymeric chains were synthesized by a single step reaction between commercially available group 4 metallocene dichlorides [Cp₂MCl₂] (M = Ti, Zr, Hf; Cp = η^5$-C5 H$_5$), pentaphosphaferrocene [Cp*Fe($η^5$ -P$_5$ )] (Cp* = $η^5$-C$_5$Me$_5) and potassium metal. These reactions selectively gave polymeric chains of radical, [KCp_2M_2(η^4$ -P$_5)FeCp*2 ]n (M = Ti, Zr, Hf). The four membered P_2M_2$ core is the first example of such a phosphorus-based ring with a radical anionic nature. Moreover, it is also a rare example of a main group element based radical polymeric chain. The radical nature of the metallopolymer is further established by EPR, XANES and quantum chemical calculations. The potassium ion acts as a linker ion between two [{Cp₂M}{(η⁴ -P₅)FeCp*}] fragments. The reaction of [K{Cp₂M}₂{(η⁴-P₅)FeCp*}₂]ₙ with [2.2.2]-cryptand in THF resulted in chain cleavage into charge separated monomeric complexes [(K[2.2.2]-cryptand){Cp₂M}₂ {(η⁴-P₅)FeCp*}₂] (M = Ti, Zr, Hf).