Direct Reaction - One Step Route to Synthesize Lanthanoid-iodide Formamidinates

Abstract

This paper describes a novel and simple method - direct reaction of lanthanoid metals with equimolar amounts of iodine and a formamidine under ultrasonication as an effective, metal-based route to lanthanoid(III) diiodide formamidinates, namely I. N,N'-Bis(2,6-diisopropylphenyl)formamidinatodiiodidolanthanoid(III) complexes [Ln(DippForm)I₂ (thf)₃ ] (Ln=La, 1, Ce, 2, Tb, 3, Ho, 4, Er, 5, Tm, 6); II. N,N'-Bis(2,6-diethylphenyl)formamidinatodiiodidolanthanoid(III) complexes [Ln(EtForm)I₂ (thf)₃ ] (Ln=Ce, 7, Nd, 8, Gd, 9, Tb, 10, Dy, 11, Ho, 12, Er, 13, Lu, 14). III. N,N'-bis(2,6-dimethylphenyl)formamidinatodiiodidolanthanoid(III) complexes [Ln(XylForm)I₂ (thf)₃ ] (Ln=Ce, 15, Nd, 16, Gd, 17, Tm, 18, Lu 19); IV. N,N'-bis(phenyl)formamidinatodiiodidolanthanoid complexes [Ln(PhForm)I₂ (thf)₃ ] (Ln=Nd, 20, Gd, 21, Er, 22). Compound [Ce(XylForm)₂ I(thf)₂ ] (23) was also synthesized by the same method except the ratio of I₂ to XylFormH was 1 : 4. Divalent N,N'-bis(2,6-diisopropylphenyl)formamidinato-iodido-lanthanoid(II) complexes [Eu(DippForm)I(thf)₄ ] ⋅ thf (24), [Yb(DippForm)I(thf)₃ ] ⋅ 2DippFormH (25), [Sm(DippForm)I(thf)₄ ] ⋅ thf (26) have also been synthesized by direct reactions of the free metals, iodine and DippFormH. Interestingly, [Sm(DippForm)I₂ (thf)₃ ] (27) was obtained by the oxidation of [Sm(DippForm)I(thf)₄ ] ⋅ thf (26) on exposure to air. N,N'-Bis(2,6-dimethylphenyl)formamidinatoiodidosamarium(II) [Sm(XylForm)I(thf)₃ ]_n (28) was also prepared by direct reaction of Sm, iodine and XylFormH (mole ratio of I₂ : XylFormH=1 : 2). All products have been identified by X-ray crystallography and all the trivalent complexes [Ln(Form)_n I_3-n ] (n=1 or 2) are stable to rearrangement.

Keywords: Lanthanoids; Rare earths; heteroleptic compounds; structures; synthesis.