Reactivity of the CpMn(CO) 2 −XR Bond [X = Cl, Br]: A Kinetic Study Using Rapid-Scan FTIR Spectroscopy
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The mechanism and energetics of the displacement of dihaloalkanes from the photolytically generated CpMn(CO)2-XR (X = Cl, Br) complexes by 2,6-lutidine have been studied using rapid-scan FTIR. The substitution reactions proceed through an Id mechanism, and theoretical calculations indicate that the Mn-XR bond is mostly broken in the transition state. Activation enthalpies of 16-17 kcal/mol for the Mn-ClR and 18-19 kcal/mol for the Mn-BrR complexes are only slightly lower than previous thermodynamic measurements of the Mn-haloalkane bond dissociation enthalpies. The rate of displacement of bromoalkanes was found to be ∼10 times slower than for the analogous chloroalkanes. Ab initio calculations suggest that this difference in reactivity is primarily due to a more stable interaction between the Mn center and bromoalkanes. © 2008 American Chemical Society.
author list (cited authors)
Bengali, A. A., & Fan, W. Y.