Lanthanoid Pseudo-Grignard Reagents: A Major Untapped Resource

Chemistry. 2018 Jan 2;24(1):230-242. doi: 10.1002/chem.201704383. Epub 2017 Dec 5.

Abstract

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)2 I(dme)]⋅dme (7 b) {(Form=ArNCHNAr; XylForm (Ar=2,6-Me2 C6 H3 ), MesForm (Ar=2,4,6-Me3 C6 H2 ), DippForm (Ar=2,6-iPr2 C6 H3 )}. 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(Ph2 pz)I(thf)4 ] (Ph2 pz=3,5-diphenylpyrazolate) was oxidised with 1,2-diiodoethane to afford seven-coordinate monomeric pyrazolato-ytterbium(III) iodide [Yb(Ph2 Pz)I2 (thf)3 ] (8) in high yield, whilst metathesis between [Yb(Ph2 pz)I(thf)4 ] and NaCp (Cp=C5 H5 ) gave [Yb(C5 H5 )(Ph2 pz)(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.

Keywords: LnLX-type complexes; X-ray diffraction; europium; formamidines; organolanthanoid complexes; ytterbium.