LANTHANIDES

Organometallic Chemistry

• Organolanthanide chemistry is not as extensive as organotransition metal chemistry,
• Currently receiving a lot of attention, especially inC-H Bond Activation studies
• Primarily ionic in their bonding Ð contracted nature of the 4f valence orbitals
• Lanthanides cannot act as p-bases Þ Ln-CO compounds are not stable
• Organolanthanides are extremely air & moisture sensitive

  ~ reflects highly carbanionic character of organic ligand & oxophilicity of Ln^2+/3+

Cyclopentadienides (C₅H₅^- ligand)

Preparation:

Structure:

Also in+2 Oxidation State

Alkyls & Aryls

• s-bonded alkyls & aryls
• from metathesis in ether/thf
  • R = phenyl probably polymeric
  • R = CH₂CMe₃ stable as LnR₃(thf)₂
• [LnMe₆]^3- have been isolated for most Ln

Mixed Alkyl Cyclopentadienides

• C₅Me₅ (Pentamethyl-cyclopentadienyl) is a common organo-Ln ligand
  • large bulk Þ only 2 C₅Me₅ may be bound to Ln
  • causes major change in structural & chemical properties
  • especially novel chemistry in mixed alkyl cyclopentadienides

    e.g. (C₅Me₅)₂LuCH₃

    Æ catalyzes alkene polymerization (Ziegler-Natta chemistry)

    Æ reacts with C-H bonds of extremely low acidity e.g. CH₄ !!

Cycloctatetraenide M³⁺(C₈H₈^2&endash;)₂ Sandwich Compounds

Preparation:

Structure:

• pale green crystals
• paramagnetic
• air & moisture sensitive
• planar COT rings
• staggered D_8d conformation
• solvated K⁺ interacts symmetrically with one COT ring

Arenes

Lanthanide Bis-Arene 'sandwich' compounds

• prepared by metal vapour synthesis (MVS) techniques
• stable at ambient temperature

  

• Ln⁰ - such compounds could not be expected for Ln^III with contracted 4f orbitals

For more on Lanthanide Organometallics see: R.D. Köhn et al, in Encyclopedia of Inorganic Chemistry, ed. R.B. King pp. 3618-3666