Half sandwich complexes containing cyclopentadienyl ligands are common. Well studied examples include (η-CH)V(CO), (η-CH)Cr(CO)H, (η-CHCH)Mn(CO), (η-CH)Cr(CO)H, [(η-CH)Fe(CO)], (η-CH)V(CO)I, and (η-CH)Ru(NCMe). (η-CH)Co(CO) is a two-legged piano stool complex.  Bulky cyclopentadienyl ligands such as 1,2,4-CH(tert-Bu) form unusual half-sandwich complexes.