A gas-phase study of the kinetics of formation of Fe(CO)(3)DMB, Fe(CO)(3)(DMB)(2), and Fe(CI)(4)DMB: The bond dissociation enthalpy for Fe(CO)(3)(DMB)(2) (DMB=3,3-dimethyl-1-butene)

The transient spectra of Fe(CO)(3)(3,3-dimethyl-1-butene) and Fe(CO)(3)(3,3 -dimethyl-1-butene)(2) have been obtained in the carbonyl stretching region of the infrared. Fe(CO)(4)(3,3-dimethyl-1-butene) has also been monitored. The bond dissociation enthalpy for loss of 3,3-dimethyl-1-butene (DMB) fro m Fe(CO)3(DMB)2 has been determined as 15.2 +/- 3.8 kcal mol(-1). The rate constants for the reactions of Fe(CO)(3) + DMB, Fe(CO)(3)DMB + DMB, Fe(CO)( 4) + DMB, and Fe(CO)(3)DMB + CO have been measured as (9.6 +/- 1.4) x 10(-1 1), (2.3 +/- 0.8) x 10(-12), (5.0 +/- 0.5) x 10(-13), and (3.9 +/- 0.6) x 1 0(-12) cm(3) molecule(-1) s(-1), respectively. The effects of the polarizab ility and steric interaction energy of the ligand on the bimolecular rate c onstants for the reactions of Fe(CO)(3)L + L (L = olefin) complexes are dis cussed. A correlation between these rate constants and the steric interacti on energy divided by the magnitude of the polarizability of the ligand is o bserved. An estimate for the rate constant for addition of 1-pentene to Fe( CO)(3)(l-pentene), based on data and correlations from this study, does not lead to a significant change in calculated thermodynamic parameters for pr ocesses relevant to the isomerization of pentene. Factors that: could influ ence the stability of Fe(CO)(3)L-2 complexes are also discussed.