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Keywords:

  • cluster compounds;
  • cyclopentadienyl ligands;
  • hydrides;
  • rare earths;
  • sandwich complexes

Abstract

The acid–base reaction of [Ln(CH2SiMe3)3(thf)2] with Cp′H gave the corresponding half-sandwich rare earth dialkyl complexes [(Cp′)Ln(CH2SiMe3)2(thf)] (1-Ln: Ln=Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; Cp′=C5Me4SiMe3) in 62–90 % isolated yields. X-ray crystallographic studies revealed that all of these complexes adopt a similar overall structure, in spite of large difference in metal-ion size. In most cases, the hydrogenolysis of the dialkyl complexes in toluene gave the tetranuclear octahydride complexes [{(Cp′)Ln(μ-H)2}4(thf)x] (2-Ln: Ln=Sc, x=0; Y, x=1; Er, x=1; Tm, x=1; Gd, x=1; Dy, x=1; Ho, x=1) as the only isolable product. However, in the case of Lu, a trinuclear pentahydride [(Cp′)2Lu3(μ-H)5(μ-CH2SiMe2C5Me4)(thf)2] (3), in which the C[BOND]H activation of a methyl group of the Me3Si unit on a Cp′ ligand took place, was obtained as a major product (66 % yield), in addition to the tetranuclear octahydride [{(Cp′)Lu(μ-H)2}4(thf)] (2-Lu, 34 %). The use of hexane instead of toluene as a solvent for the hydrogenolysis of 1-Lu led to formation of 2-Lu as a major product (85 %), while a similar reaction in THF yielded 3 predominantly (90 %). The tetranuclear octahydride complexes of early (larger) lanthanide metals [{Cp′Ln(μ-H)2}4(thf)2] (2, Ln=La, Ce, Pr, Nd, Sm) were obtained in 38–57 % isolated yields by hydrogenolysis of the bis(aminobenzyl) species [Cp′Ln(CH2C6H4NMe2-o)2], which were generated in-situ by reaction of [Ln(CH2C6H4NMe2-o)3] with one equivalent of Cp′H. X-ray crystallographic studies showed that the fine structures of these hydride clusters are dependent on the size of the metal ions.