Reactivity of cyclopentadienyl and indenyl alkylcarbonyliron(II) complexes. η5 Species as key intermediates in the migratory insertion of carbon monoxide

Abstract

The reactions of the complexes [Fe(η⁵-L)(CO)₂R](L = C₅H₅ or C₉H₇, R = Me or CHMe₂) with PR′₃(PMe₂Ph, PMePh₂ and PPh₃) have been studied in toluene and tetrahydrofuran (thf) by UV/VIS and IR spectroscopy. The products of alkyl migratory insertion [Fe(η⁵-C₅H₅)(CO)(COR)(PR′₃)] are formed via an associative mechanism, involving (i) a rapid pre-equilibrium (K) between complex and phosphine and (ii) rate-determining alkyl migration (k₂), in analogy to the mechanism previously established for [Fe(η⁵-C₉H₇)(CO)₂R]. In the intermediate molecular complexes {[Fe(η⁵-L)(CO)₂R], phosphine} the compounds [Fe(η⁵-C₅H₅)(CO)₂R] bind to phosphine less efficiently than do the indenyl analogues and react one order of magnitude more slowly. Reaction rates are similar in thf and in toluene, in agreement with the proposal that the alkyl migration is not solvent assisted.