Synthesis, structure, reactivity, and diastereoisomer separation of (Tropone)fe(co)₂l complexes (l = pph₃, (+)-neomenthyldiphenylphosphine)

The title complexes have been prepared by amine oxide substitution of (tropone)Fe(CO)₃. The solid-state molecular structure of (tropone)Fe(CO)₂PPh₃ reveals a distorted-square-pyramidal geometry with a basal PPh₃ trans to the keto-substituted C═C bond; in solution, both basal isomers are populated. Rates of normal and inverse electron demand cycloaddition, and of sigmahaptotropic rearrangement, are much enhanced relative to those for the tricarbonyl. The (tropone)Fe(CO)₂((+)-neomenthyldiphenylphosphine) diastereoisomer of 6S planar chirality may be isolated by crystallization. Though the rate of the 1,3-shift is enhanced relative to that for the tricarbonyl, normal and inverse electron demand cycloadditions and electrophilic attack proceed under mild conditions without racemization of the planar chirality.