Cyclopentadienyl (Cp) ligands in moderately strained [1]- and [2]ferrocenophanes [Fe{(eta(5)-C5H4)(2)(ERx)(y)}: Fe{(eta(5)-C5H4)(2)SiMe2) (1), Fe{(eta(5)-C5H4)CH2}(2) (10)] and highly strained [2]ruthenocenophanes (Ru{(eta(5)-C5H4)CR2}(2) {R = H(15), Me (16)}] are susceptible to partial substitution by P donors and form mixedhapticity metallocycles-[M(L-2){(eta(5)-C5H4)(ERx)(y)(eta(1)-C5H4)}]: [Fe(dppe){(eta(5)-C5H4)SiMe2(eta(1)-C5H4)}] (5), [Fe(dmpe){(eta(5)-C5H4)SiMe2(eta(1)-C5H4)}] (6), [Fe(dmpe){(eta(5)-C5H4)(CH2)(2)(eta(1)-C5H4)}] (11), [Ru(dmpe){(eta(5)-C5H4)(CH2)(2)(eta(1)-C5H4)}] (17), [Ru(dmpe){(eta(5)-C5H4)(CMe2)(2)(eta(1)-C5H4)}] (18), and [Ru(PMe3)(2){(eta(5)-C5H4)(CH2)(2)(eta(C5H4)-C-1)}] (19)-through haptotropic reduction of one eta(5-), pi-bound Cp to eta(1), sigma-coordination. These reactions are strain-controlled, as highly ring-tilted [2]ruthenocenophanes 15 and 16 [tilt angles(alpha) approximate to 29-31 degrees] react without irradiation to form thermodynamically stable products, while moderately strained [n]ferrocenophanes 1 and 10 (alpha approximate to 19-22 degrees) require photoactivation. The iron-containing photoproducts 5 and 11 are metastable and thermally retroconvert to their strained precursors and free phosphines at 70 degrees C. In contrast, the unprecedented ring-opening polymerization (ROP) of the essentially ring-strain-free adduct 6 to afford poly(ferrocenyldimethylsilane) [Fe(eta(5)-C6H4)(2)SiMe2](n) (M-w approximate to 5000 Da) was initiated by the thermal liberation of small amounts of P donor. Unlike reactions with bidentate analogues, monodentate phosphines promoted photolytic ROP of ferrocenophanes 1 and 10. MALDI-TOF analysis suggested a cyclic structure for the soluble poly(ferrocenyldimethylsilane), 8-cyclic, produced from 1 in this manner. While the polymer likewise produced from 10 was insoluble, the initiation step in the ROP process was modeled by isolation of a tris(phosphine)-substituted ring-opened ferrocenophane [Fe(PMe3)(3){(eta(5)-C5H4)(CH2)(2)(C5H5)}][OCH2CH3] (13[OCH2CH3]) generated by irradiation of 10 and PMe3 in a protic solvent (EtOH). Studies of the cation 13 revealed that the Fe center reacts with a Cp-anion with loss of the phosphines to form [Fe(eta(5)-C5H5){(eta(5)-C5H4)(CH2)(2)(C5H5)}] (14) under conditions identical to those of the ROP experiments, confirming the likelihood of "back-biting" reactions to yield cyclic structurs or macroconclensation to produce longer chains.