Lanthanoid Pseudo‐Grignard Reagents: A Major Untapped Resource

Pseudo‐Grignard reagents PhLnI (Ln=Yb, Eu), readily prepared by the oxidative addition of iodobenzene to ytterbium or europium metal at −78 °C in tetrahydrofuran (THF) or 1,2‐dimethoxyethane (DME), react with a range of bulky N,N′‐bis(aryl)formamidines to generate an extensive series of LnII or more rarely LnIII complexes, namely [Eu(DippForm)I(thf)4]⋅thf (1), [{EuI2(dme)2}2] (2), [Eu(XylForm)I(dme)2]⋅0.5 dme (3 a), [Eu(XylForm)I(dme)(μ‐dme)]n (3 b), [{Eu(XylForm)I(μ‐OH)(thf)2}2] (4), [Yb(DippForm)I(thf)3]⋅thf (5 a), [Yb(DippForm)I2(thf)3]⋅2 thf (5 b), [{Yb(MesForm)I(thf)2}2] (6), [{Yb(XylForm)I(thf)2}2] (7 a), and [Yb(XylForm)2I(dme)]⋅dme (7 b) {(Form=ArNCHNAr; XylForm (Ar=2,6‐Me2C6H3), MesForm (Ar=2,4,6‐Me3C6H2), DippForm (Ar=2,6‐iPr2C6H3)}. Reaction of PhEuI and MesFormH in DME consistently gave 2, and reaction with XylFormH in THF gave 4. Europium complexes 1 and 3 a are seven‐coordinate divalent monomers, whilst 3 b is a seven‐coordinate dme‐bridged polymer. Complex 5 a of the smaller YbII is a six‐coordinate monomer, but the related 6 and 7 a are six‐coordinate iodide‐bridged dimers. 4 is a trivalent seven‐coordinate hydroxide‐bridged dimer, whereas complexes 5 b and 7 b are seven‐coordinate monomeric YbIII derivatives. A characteristic structural feature is that iodide ligands are cisoid to the formamidinate ligand. To illustrate the synthetic scope of the pseudo‐Grignard reagents, [Yb(Ph2pz)I(thf)4] (Ph2pz=3,5‐diphenylpyrazolate) was oxidised with 1,2‐diiodoethane to afford seven‐coordinate monomeric pyrazolato‐ytterbium(III) iodide [Yb(Ph2Pz)I2(thf)3] (8) in high yield, whilst metathesis between [Yb(Ph2pz)I(thf)4] and NaCp (Cp=C5H5) gave [Yb(C5H5)(Ph2pz)(thf)]n (9), a nine‐coordinate η5:η5‐Cp‐bridged coordination polymer. Reaction of the pseudo‐Grignard reagent MeYbI with KN(SiMe3)2 gave [K(dme)4][Yb{N(SiMe3)2}3] (10) with a charge‐separated three‐coordinate homoleptic [Yb{N(SiMe3)2}3]− anion, a complex that could be obtained in high yield by deliberate synthesis from YbI2 and KN(SiMe3)2 in DME. Exploiting PhLnX reagents: Pseudo‐Grignard reagents PhLnX (Ln=Yb, Eu; X=I) have been prepared by treatment of iodobenzene with lanthanoid metals (ytterbium or europium metal). These PhLnX reagents react with a range of the readily prepared and sterically tunable N,N′‐bis(aryl)formamidines to form an extensive series of LnII or LnIII complexes (see graphic).