In the area of

organometallic chemistry Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...

, a bulky cyclopentadienyl ligand is

jargon Jargon, or technical language, is the specialized terminology associated with a particular field or area of activity. Jargon is normally employed in a particular Context (language use), communicative context and may not be well understood outside ...

for a ligand of the type where R is a branched

alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...

and ''n'' = 3 or 4. Representative examples are the tetra

isopropyl In organic chemistry, a propyl group is a three-carbon alkyl substituent with chemical formula for the linear form. This substituent form is obtained by removing one hydrogen atom attached to the terminal carbon of propane. A propyl substituent ...

derivative and the tris( ''tert''-butyl) derivative . These ligands are so large that their complexes behave differently from the

pentamethylcyclopentadienyl 1,2,3,4,5-Pentamethylcyclopentadiene is a cyclic diene with the formula , often written , where Me is . It is a colorless liquid. 1,2,3,4,5-Pentamethylcyclopentadiene is the precursor to the ligand ''1,2,3,4,5-pentamethylcyclopentadienyl'', whi ...

analogues. Because they cannot closely approach the metal, these bulky ligands stabilize high spin complexes, such as (C₅H₂^''t''Bu₃)₂Fe₂I₂. These large ligands stabilize highly unsaturated derivatives such as (C₅H₂^''t''Bu₃)₂Fe₂N₂.

Synthesis and reactions

The (''tert''-butyl)cyclopentadiene is prepared by alkylation of

cyclopentadiene Cyclopentadiene is an organic compound with the chemical formula, formula C5H6. It is often abbreviated CpH because the cyclopentadienyl anion is abbreviated Cp−. This colorless liquid has a strong and unpleasant odor. At room temperature, ...

with ''tert''-butyl bromide in the presence of

sodium hydride Sodium hydride is the chemical compound with the empirical formula Na H. This alkali metal hydride is primarily used as a strong yet combustible base in organic synthesis. NaH is a saline (salt-like) hydride, composed of Na+ and H− ions, in co ...

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 Metal nitrido complexes are coordination compounds and metal clusters that contain an atom of nitrogen bound only to transition metals. These compounds are ''molecular'', i.e. discrete in contrast to the polymeric, dense nitride materials that are ...

(^''t''Bu₃C₅H₂)₂Fe₂N₂. In contrast to (C₅Me₅)₂Ir₂Cl₄, (^''t''Bu₃C₅H₂)IrCl₂ is monomeric.

References

{{Organometallics * Organometallic chemistry