A Gas-Phase Study of the Kinetics of Formation of Fe(CO)₃DMB, Fe(CO)₃(DMB)₂, and Fe(CO)₄DMB:  The Bond Dissociation Enthalpy for Fe(CO)₃(DMB)₂ (DMB = 3,3-dimethyl-1-butene)

Abstract

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) from 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) × 10 -11 , (2.3 ( 0.8) × 10 -12 , (5.0 ( 0.5) × 10 -13 , and (3.9 ( 0.6) × 10 -12 cm 3 molecule -1 s -1 , respectively. The effects of the polarizability and steric interaction energy of the ligand on the bimolecular rate constants for the reactions of Fe(CO) 3 L + L (L ) olefin) complexes are discussed. A correlation between these rate constants and the steric interaction energy divided by the magnitude of the polarizability of the ligand is observed. An estimate for the rate constant for addition of 1-pentene to Fe(CO) 3 (1-pentene), based on data and correlations from this study, does not lead to a significant change in calculated thermodynamic parameters for processes relevant to the isomerization of pentene. Factors that could influence the stability of Fe(CO) 3 L 2 complexes are also discussed.

An Experimental Determination of the Cr−DMB (DMB = 3,3-Dimethyl-1-butene) Bond Energy in Cr(CO)5(DMB): Effects of Alkyl Substitution on Chromium−Olefin Bond Energies in Cr(CO)5(olefin) Complexes

“…DMB has been chosen because it is similar to ethylene except that a “bulky” tert -butyl group substitutes for one of the hydrogens of ethylene. On the basis of prior work, we hypothesize that the presence of a tert -butyl substituent should lead to repulsive interactions which are expected to reduce the Cr−DMB BDE relative to the chromium−ethylene BDE in Cr(CO) 5 (C 2 H 4 ).…”