NMR spectroscopic study of the adduct formation and reactivity of homoleptic rare earth amides with alkali metal benzyl compounds, and the crystal structures of [Li(TMEDA)2][Nd{N(SiMe3)2}3(CH2Ph)] and [{Li(TMP)}2{Li(Ph)}

Abstract

An NMR spectroscopic study has been conducted into the reactivity of alkali metal benzyls [M(CH2Ph)], (M = Li, Na, K) with lanthanide tris(amide) complexes [Ln(N″)3] (Ln = Y, Ce, Nd; N″ = N(SiMe3)2) and [Ce(TMP)3] (TMP = 2,2,6,6-tetramethylpiperidide). It was found that for [Ln(N″)3], benzyl adducts [M][Ln(N″)3(CH2Ph)] were initially formed, and the molecular structure for M = Li(TMEDA)2 and Ln = Nd was determined revealing a distorted tetrahedral [Nd(N″)3(CH2Ph)] anion. In all cases, these adduct complexes were unstable, intramolecularly deprotonating a methyl arm of a N″ ligand via benzyl basicity and eliminating toluene to prepare cyclometallated complexes of the form [M][Ln(N″)2{κ2-CH2Si(Me)2N(SiMe3)}]. In parallel studies, reactions of [Li(Ph)] with [Ln(N″)3] (Ln = Ce, Nd) afforded [Li(N″)], whilst for (Ln = Y) adduct formation was observed. [Ce(TMP)3] did not generate any characterisable bimetallic adducts. The reaction of [Li(Ph)] with [Li(TMP)] afforded the hexanuclear [{Li(TMP)}2{Li(μ-Ph)}]2, which features lithium in three different coordination environments.