Full P ₄ to P ³⁻ Reduction with a Redox‐Active Metal Crown Complex

Abstract

Abstract Traditional bulk syntheses of phosphorus compounds start with P 4 to PCl 3 oxidation but more sustainable methods cleave P─P bonds reductively. This generally results in larger polyphosphide Zintl anions: P m n ˉ. We report a relatively selective full reduction of P 4 at room temperature to give a unique hydrocarbon‐soluble s ‐block metal complex of the P 3 ˉ anion. Key to this chemistry is a recently reported redox‐active metal crown complex: (BDI*)MgNa 3 N″ 2 ( VI ); N″ = N(SiMe 3 ) 2 and BDI* = HC[( t Bu)C═N‐DIPeP] 2 , DIPeP = 2,6‐CHEt 2 ‐phenyl. The reduction of P 4 according to 2 VI  + 0.25 P 4  → (BDI*)MgNa 5 N″ 3 P ( 1 ) + 0.5 [(BDI*)Mg] 2  + 0.33 (NaN″) 3 is calculated to be exothermic (Δ H  = −40.5 kcal mol −1 ). The crystal structure of 1 shows a strongly bound (BDI*)MgP 2 ˉ anion with two chelating [Na‐N″‐Na + ] and [Na‐N″‐Na‐N″‐Na + ] arms of unequal length. Although these arms are highly fluxional and rapidly exchange ions, they effectively stabilize the P 3 ˉ anion. DFT calculations confirm the highly ionic nature of the complex and describe P 3 ˉ as full valence‐shell anion with four lone‐pairs of electrons. Reactivity studies show that the P 3 ˉ anion can react as a triple Brønsted base, a three‐fold nucleophile or as a reducing agent.