The complexes [Fe(CO)_{3 –n}L_n(η⁴-cot)][1: cot = cyclo-octatetraene; n= 0–3, L = P(OMe)₃; n= 1, L = P(NMe₂)₃, PPh₃, P(OCH₂)₃CMe, or P(OPh)₃] undergo chemically irreversible one-electron oxidation in CH₂Cl₂ at a platinum electrode. Chemical generation of the highly reactive radical cation [Fe(CO)₂L(C₈H₈)]⁺[2; L = CO or P(OPh)₃], by oxidation of (1) with silver(I) salts or [N(C₆H₄Br-p)₃][PF₆], is followed by isomerisation and dimerisation, via C–C bond formation, to give [Fe₂(CO)_{6 –n}L_n(η⁵:η′⁵-C₁₆H₁₆)]²⁺[3; n= 0 or 2, L = P(OPh)₃]. The crystal structure of [3; n= 2, L = P(OPh)₃], as the [PF₆]^– salt, reveals the presence of a dimeric C₁₆H₁₆ unit comprising two fused ring systems bonded to one another across a two-fold crystallographic axis of symmetry. The five unbridged carbon atoms of the C₇ ring are coplanar and η⁵-bonded to the iron atom, which in turn is orthogonally co-ordinated to the two CO ligands and the P(OPh)₃ group. The C₇ ring folds away from the metal atom, and there are further folds at the junction with the C₃ ring and again at the apex of the C₃ ring, all in the same sense. The dimeric ligand thus has an overall S shape when viewed down the two-fold axis. Along the Fe ⋯ Fe vector, by contrast, the C₃ rings are seen edgewise and the two C₇ rings are almost eclipsed. Complex (3; n= 0) reacts with Na[BH₄] to give [Fe₂(CO)₆(η⁴:η′⁴-C₁₆H₁₈)](4). With halide ion, however, (3; n= 0) affords [Fe(CO)₃(η⁴-C₁₆H₁₆)](5)via reductive C–C coupling. X-Ray analysis shows that in complex (5) a further link between the two halves of the dimer has been formed, in that the fifth C atom of the C₇ ring which in (3) was bonded to the metal atom is now bonded to its counterpart in the other half of the dimer, forming an additional central C₆ ring. As might be expected, the C₇ ring which is not co-ordinated to iron is more nearly planar and the C–C bonds are more localised. With [Fe₂(CO)₉], complex (5) yields [Fe₂(CO)₆(η⁴:η′⁴-C₁₆H₁₆)](6), but with NMe₃O·2H₂O in refluxing benzene, ring detachment results in the isolation of the free polycyclic hydrocarbon, C₁₆H₁₆(7).