Mono-, di-, tri- and tetranuclear rare earth complexes obtained using a moderately bulky aryloxide ligand

Redox transmetallation ligand exchange reactions involving a rare earth metal, 2,4,6-trimethylphenol (HOmes), and a diarylmercurial afford rare earth aryloxo complexes, which are structurally characterized. Both the lanthanoid contraction and the identity of the reaction solvent are found to influence the outcome of the reactions. Using THF in the reaction affords a dinuclear species [Ln2(Omes)6(thf)4].2THF (Ln=La 1, Nd 2) for the lighter rare earth metals, while a mononuclear species [Ln(Omes)3(thf)3] (Ln=Sm 3, Tb 5, Er 6, Yb 7, Y 8) is obtained for the heavier rare earth elements. Surprisingly, there is no change in metal coordination number between the two structural motifs. A divalent trinuclear linear complex [Eu3(Omes)6(thf)6] 4 is obtained for Eu, and features solely bridging aryloxide ligands. Using DME as the reaction solvent affords [La(Omes)3(dme)2] 9 from the reaction mixture, and [Ln2(Omes)6(dme)2].PhMe (La 10, Nd 11) and [Y(Omes)3(dme)2] 14 following crystallization of the crude product from toluene. The dinuclear species [Eu2(Omes)4(dme)4] 12 contains two unidentate and two chelating DME ligands, and contrasts the linear structure of 4. Treatment of HOmes and HgPh2 with Yb metal in DME affords the mixed valent Yb(II/III) complex [Yb2(Omes)5(dme)2] 13, which is stabilized by an intramolecular pi-Ph-Yb interaction, and is a rare example of a mixed valent rare earth aryloxide. Treatment of Er metal with HOmes at elevated temperature (solvent free) affords the homoleptic [Er4(Omes)12] 15, which consists of a tetranuclear array of Er atoms arranged in a 'herringbone' fashion; the structure is stabilized by intramolecular pi-Ph-Er interactions. Reaction of La metal with HOmes under similar conditions yields toluene insoluble "La(Omes)3", which affords 1 following extraction with THF.