Manipulation of reaction pathways in redox transmetallation–ligand exchange syntheses of lanthanoid(ii)/(iii) aryloxide complexes

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Abstract
Redox transmetallation/ligand exchange reactions of lanthanoid metals (Ln), Hg(C6F5)2 and HOArOMe (ArOMe = C6H2-2,6-But-4-OMe), in thf (tetrahydrofuran) gave, for Ln = Yb, [Yb(OArOMe)2(thf)3], and for Ln = Sm, a mixture of [SmII(OArOMe)2(thf)3] and mainly [SmIII(ArOMe)3(thf)]·thf. X-Ray structure determinations show the divalent complexes to have distorted square-pyramidal stereochemistry with transoid thf and OArOMe ligands in the basal plane. Treatment of [Yb(OArOMe)2(thf)3] with diethyl ether or PhMe at room temperature gave [Yb(OArOMe)2] or [Yb(OArOMe)2]·0.5PhMe. For lanthanoids Ln = Nd, Er or Y, the reactions with Hg(C6F5)2 and HOArOMe yielded complex product mixtures, from one of which the novel erbium aryloxide fluoride cage [Er3(OArOMe)4(μ2-F)3(μ3-F)2(thf)4]·thf·0.5C6H14 was isolated. The cage core consists of a triangle of Er atoms joined to two μ3-fluoride ligands and three further μ2-fluorides bridge adjacent Er atoms. One of the Er atoms is six-coordinate with additionally two OArOMe ligands whilst the other two have one OArOMe and two thf ligands and are seven coordinate. Substitution of Hg(C6F5)2 by Hg(CCPh)2 in the redox transmetallation/ligand exchange reactions gave the new derivatives [Ln(OArOMe)3(thf)]·thf (Ln = La, Pr, Nd, Sm, Gd, Ho) in good yields whilst Ln = Yb gave [Yb(OArOMe)2(thf)3]. Recrystallisation of [Sm(OArOMe)3(thf)]·thf from dme (1,2-dimethoxyethane) yielded [Sm(OArOMe)3(dme)]. Structural characterisation of [Ln(OArOMe)3(thf)]·thf (Ln = Nd, Ho) and [Sm(OArOMe)3(dme)] showed monomeric four-coordinate distorted tetrahedral and five-coordinate distorted square-pyramidal complexes respectively. For the smaller lanthanoids Ln = Y, Er or Lu, reactions with Hg(CCPh)2 and HOArOMe gave the mixed aryloxide/alkynide complexes [Ln(OArOMe)2(CCPh)(thf)2]. Oxidation of the divalent ytterbium aryloxide [Yb(OArOMe)2(thf)3] by Hg(CCPh)2 in thf gave the analogous [Yb(OArOMe)2(CCPh)(thf)2]. The erbium alkynide [Er(OArOMe)2(CCPh)(thf)2]·0.25C6H14 has distorted square-pyramidal stereochemistry with transoid OArOMe and thf ligands in the basal plane and a rare (for Ln) terminal alkynide ligand in the apical position. The reactive Lu–C bond in the [Lu(OArOMe)2(CCPh)(thf)2] complexes could be slowly cleaved by free HOArOMe in hydrocarbon solvents, yielding Lu(OArOMe)3 species and fortuitous partial hydrolysis of [Er(ArOMe)2(CCPh)(thf)2] gave the dimeric [Er(OArOMe)2(μ-OH)2]2.

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