Kinetics and mechanism of mono- and di-olefin exchange at five-co-ordinate iron(0)

Abstract

Exchange of various mono-olefins with styrene in [Fe(CO)₄(PhCHCH₂)] proceeds via a dissociative process, involving an Fe(CO)₄ intermediate. Ligand exchange in system (i)(enone = benzylideneacetone, cinnamaldehyde, chalcone, or dypnone; polyene = cyclohexa- and cyclohepta-1,3-diene, cycloheptatriene, cycle-octatetraene, [Fe(CO)₃(η⁴-enone)]+ polyene ⇌[Fe(CO)₃(η⁴-polyene)]+ enone (i) or 1,4-diphenylbuta-1,3-diene) is stepwise, involving a rate-determining dechelation of the π-bound CO moiety. Both associative and dissociative pathways are found. The influence of diene structure and enone substituent is discussed.