In the area of organometallic chemistry, a bulky cyclopentadienyl ligand is jargon for a ligand of the type  where R is a branched alkyl and n = 3 or 4.  Representative examples are the tetraisopropyl derivative  and the tris(tert-butyl) derivative .  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 (CHBu)FeI.  These large ligands stabilize highly unsaturated derivatives such as (CHBu)FeN.