Kinetic studies on the reactions of the tricarbonyl(1–3,6-η-cyclo-octadiene)-iron and -ruthenium complexes with tertiary phosphines and phosphites

Abstract

The complex [(1–3,6-η-C₈H₁₂)Fe(CO)₃](1–3,6-η-C₈H₁₂= 1–3,6-η-cyclo-octadiene), (Ia), when treated with tertiary phosphines L (L = triphenylphosphine or triphenyl phosphite) in n-heptane (40–70 °C) produces the monosubstituted derivative [(1–3,6-η-C₈H₁₂)Fe(CO)₂L], (IIa), via a CO-dissociative mechanism. Observed pseudo-first-order rate constants for reaction with a range of more nucleophilic phosphorus ligands (for example methyl phosphite) are given by the relation k_obs=k₁+k₂[L]. The ligand-independent term corresponds to formation of the carbonyl-substituted derivative and the ligand-dependent term to formation of the complexes [Fe(CO)₂L₃], (IIa), and the trans-annular ketone C₉H₁₂O, (III). Studies of the analogous ruthenium system show that dissociation of CO (at 40 °C) is ca. 40 times greater than that of the iron complex. This results from a more favourable enthalpy of activation. However, no second-order reaction of this complex has been detected.