The enhanced reactivity of [Fe(eta-C5H4CH 2)2] with ultraviolet irradiation allows for stoichiometric ring-opening by alkyl Cp anions [C5H4R]- (R = Me, tBu) via attack at an Fe-Cp bond. The reactivity of the photo-excited monomer towards various initiators has been examined. Short, linear, partially-soluble oligomers of the type [fcCH 2CH2]x (x = 3, 4) were prepared.Reversible, haptotropic shifts of cyclopentadienyl (Cp) ligands in moderately strained [1]- and [2]metallocenophanes [Fe(eta-C5H 4)2SiMe2] and [Fe(eta-C5H4CH 2)2] have been studied. These complexes, stable as ansa metallocenes in solution, appear to form ring-slipped species on UV photo-irradiation in strong donor solvents.Similar but irreversible haptotropic shifts of cyclopentadienyl ligands in highly strained [2]metallocenophanes [Ru(eta-C5H4CH 2)2] and [Ru(eta-C5H4(CMe)2 )2] have been shown to proceed without photo-initiation.The presence of monodentate or chelating phosphines allowed for the isolation of novel eta1-Cp ring-slipped complexes. At elevated temperatures, these products retroconvert to reform the ansa metallocene, freeing the coordinated phosphine.