Syntheses of Pyrazolato‐ and Formamidinato‐lanthanoid(III) diiodides from in situ generated lanthanoid(III) pseudo‐Grignard reagents

Trivalent lanthanoid pseudo‐Grignard reagents PhpLnIIII(3‐p) (Ln = La, Ce, Nd, Er and Lu) are readily prepared by the oxidative addition of iodobenzene to the lanthanoid metal 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 PhpLnIIII(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 (4a) 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; complexes 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.