Bulky cyclopentadienyl ligands

In the area of organometallic chemistry, a bulky cyclopentadienyl ligand is jargon for a ligand of the type C5H5−nR−n where R is a branched alkyl and n = 3 or 4.

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, such as (C5H2tBu3)2Fe2I2.

These large ligands stabilize highly unsaturated derivatives such as (C5H2tBu3)2Fe2N2.

This compound is conveniently prepared by alkylation of cyclobutadiene with tert-butyl bromide under phase-transfer conditions.