Ferrocenes derived from cyclopenta[l]phenanthrene: dibenzindene–metal complexes that resist haptotropic shifts

The complexes (η5-cyclopenta[l]phenanthrenyl)MLn, where MLn=Fe(C5H5), Fe(C17H11), Mn(CO)3 or Rh(C2H4)2 show no propensity to undergo η5 to η6 haptotropic shifts upon protonation, nor to undergo ready replacement of a carbonyl or ethylene ligand by a phosphine. Thus, these systems mimic the behavior of cyclopentadienyl rather than indenyl rings. Molecular orbital calculations on (C17H11)Fe(C5H5) indicate that migration of an organometallic fragment from a peripheral arene into the five-membered ring is thermodynamically favorable, but that a least-motion pathway passing through the central six-membered ring is strongly disfavored. Attempted synthesis of (η6-cyclopenta[l]phenanthrene)Cr(CO)3 gave instead the corresponding dihydro complex, (C17H13)Cr(CO)3, and the Diels–Alder dimer of cyclopenta[l]phenanthrene with its own isoindene.