page_title: Bulky cyclopentadienyl ligands
section_title: Synthesis and reactions
hierarchical_section_title: Bulky cyclopentadienyl ligands / Synthesis and reactions
caption_attribution_description: English: structure of Cp"2Fe2N2
context_page_description: In the area of organometallic chemistry, a bulky cyclopentadienyl ligand is jargon for a ligand of the type C₅H5−nRₙ⁻ where R is larger than n-alkyl and n = 3 or 4. Representative examples are the tetraisopropyl derivative C₅H(ⁱPr)₄⁻ and the tris tert-butyl derivative 1,2,4-C₅H₂(tert-Bu)₃⁻. These ligands are so large that their complexes behave differently from the pentamethylcyclopentadienyl analogues. Because they cannot closely approach the metal, these bulky ligands stabilize high spin complexes, e.g. (C₅H₂(tert-Bu)₃)₂Fe₂I₂. These large ligands stabilize highly unsaturated derivatives such as (C₅H₂(tert-Bu)₃)₂Fe₂N₂.
context_section_description: The (tert-butyl)cyclopentadiene is  prepared by alkylation of cyclopentadiene with tert-butyl bromide in the presence of sodium hydride and dibenzo-18-crown-6. The intermediate in this synthesis is di-tert-butylcyclopentadiene.  This compound is conveniently prepared by alkylation of cyclobutadiene with tert-butyl bromide under phase-transfer conditions.
  Illustrative of the unusual complexes made possible with these bulky ligands is molecular iron nitrido complex ((t-Bu)₃C₅H₂)₂Fe₂N₂.  In contrast to (C₅Me₅)₂Ir₂Cl₄, ((t-Bu)₃C₅H₂)IrCl₂ is monomeric.
caption: Structure of ((t-Bu)3C5H2)2Fe2N2.
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