Reductive Activation of White Phosphorus to [P ₄ ] ^2– , [P ₂ ] ^2– , and a Formal P ^2– Radical by Rare‐Earth Dinitrogen Complexes

Abstract

ABSTRACT Activation of white phosphorus (P 4 ) to smaller P n units by rare‐earth compounds remains a synthetic challenge. Here, we show that the rare‐earth dinitrogen complexes [{(Cp ttt ) 2  M} 2 (μ‐1,2‐N 2 )] (M = Y, Gd; Cp ttt  = 1,2,4‐tri( tert ‐butyl)cyclopentadienyl), reductively cleave P 4 to give a homologous series of phosphorus anions of decreasing nuclearity, that is, [{(Cp ttt ) 2  M} 2 (μ‐P 4 )] ( 1 M ), [{(Cp ttt ) 2  M} 2 (μ‐η 2 :η 2 ‐P 2 )] ( 2 M ), and [{(Cp ttt ) 2  M} 2 (μ‐P)] ( 3 M ). Structural, spectroscopic, and computational studies show that 1 M contains a bicyclobutane‐like [P 4 ] 2– ligand, whereas 2 M features a side‐on coordinated [P═P] 2– ligand, and 3 M comprises a monatomic P 2– ligand formulated as a phosphorus‐centered radical with S  = 1/2. The EPR spectrum of 3 Y confirms hyperfine coupling to 31 P and 89 Y, while magnetic measurements on 3 Gd reveal strong antiferromagnetic exchange between the Gd 3+ ions and the radical ligand. Density functional theory supports a three‐center π‐type M–P–M interaction in 3 M , with the unpaired spin localized primarily on phosphorus and only weak delocalization onto the metal centers. These findings represent progressive fragmentation of P 4 to diatomic and monatomic phosphorus anions by rare‐earth reagents, thereby extending the chemistry of multiply bonded phosphorus and persistent phosphorus radicals into the rare‐earth series.