Syntheses of Pyrazolato- and Formamidinato-lanthanoid(III) Diiodides from in Situ Generated lanthanoid(III) Pseudo-Grignard Reagents

Trivalent lanthanoid pseudo-Grignard reagents Ph_pLn^IIII_(3-p) (P=1 or 2; Ln=La, Ce, Nd, Er and Lu) are readily prepared by the oxidation of lanthanoid metals with iodobenzene at 25 °C, following pre-activation of the metal with 1 drop Hg in tetrahydrofuran (thf) or acetonitrile (CH₃CN) and brief sonication. The protolysis of Ph_pLn^IIII_(3-p) with 3,5-diphenylpyrazole (Ph₂pzH) yields pyrazolato complexes [Ln(Ph₂pz)I₂(thf)_n] (n=4: Ln=La 1, Ce 2, Nd 3; n=3: Ln=Er 4, Lu 5). Interestingly, for Er, a competing complex [ErPh(Ph₂pz)I(thf)₃]⋅thf (4 a) was obtained along with the expected [Er(Ph₂pz)I₂(thf)₃] (4). In contrast, in CH₃CN, [Ln(Ph₂pz)₃(CH₃CN)₃]⋅2CH₃CN (Ln=Nd 6, Gd 7) complexes were obtained through Schlenk equilibrium redistribution. Reactions with bulky N,N′-bis(2,6-di-isopropylphenyl)formamidine (DippFormH) and N,N’ –bis(2,6-dimethylphenyl)formamidine (XylFormH) produced the Ln^(III) complexes, [Ln(DippForm)I₂(thf)₃]⋅nthf (n=1, Ln=Nd 8; n=0.5, Ln=Er 9) and [Ln(XylForm)I₂(thf)₃]⋅thf (Ln=Nd 10, Er 11). All the complexes isolated in this study are monomeric; 4–5 and 8–11 are seven coordinate, complexes 1–3 are eight coordinate with one η²-N-donor ligand and two trans iodine ligands, and complexes 6–7 are nine coordinate, featuring three η²-Ph₂pz ligands, and three CH₃CN ligands.