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 degrees 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 Ln(II) or more rarely Ln(III) complexes, namely [Eu(DippForm)I(thf)(4)]center dot thf (1), [{EuI2(dme)(2)}(2)] (2), [Eu(XylForm)I(dme)(2)]center dot 0.5dme (3a), [Eu(XylForm)I(dme)(mu-dme)](n) (3b), [{Eu(XylForm)I(mu-OH)(thf)(2)}(2)] (4), [Yb(DippForm)I(thf)(3)]center dot thf (5a), [Yb(DippForm)I-2(thf)(3)]center dot 2thf (5b), [{Yb(MesForm)I(thf)(2)}(2)] (6), [{Yb(XylForm)I(thf)(2)}(2)] (7a), and [Yb(XylForm)(2)I(dme)]center dot dme (7b) {(Form=ArNCHNAr; XylForm (Ar=2,6-Me2C6H3), MesForm (Ar=2,4,6-Me3C6H2), DippForm (Ar=2,6-iPr(2)C(6)H(3))}. Reaction of PhEuI and MesFormH in DME consistently gave 2, and reaction with XylFormH in THF gave 4. Europium complexes 1 and 3a are seven-coordinate divalent monomers, whilst 3b is a seven-coordinate dme-bridged polymer. Complex 5a of the smaller Yb-II is a six-coordinate monomer, but the related 6 and 7a are six-coordinate iodide-bridged dimers. 4 is a trivalent seven-coordinate hydroxide-bridged dimer, whereas complexes 5b and 7b are seven-coordinate monomeric Yb-III 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(Ph(2)pz)I(thf)(4)] (Ph(2)pz=3,5-diphenylpyrazolate) was oxidised with 1,2-diiodoethane to afford seven-coordinate monomeric pyrazolato-ytterbium(III) iodide [Yb(Ph(2)Pz)I-2(thf)(3)] (8) in high yield, whilst metathesis between [Yb(Ph(2)pz)I(thf)(4)] and NaCp (Cp=C5H5) gave [Yb(C5H5)(Ph(2)pz)(thf)](n) (9), a nine-coordinate eta(5):eta(5)-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.