A Combined theoretical and experimental study on the role of spin states in the chemistry of fe(co)5 photoproducts

Maria Besora, José Luis Carreón-Macedo, Alexander J. Cowan, Michael W. George, Jeremy N. Harvey, Peter Portius, Kate L. Ronayne, Xue Zhong Sun, Michael Towrie

Research output: Journal PublicationArticlepeer-review

112 Citations (Scopus)

Abstract

A combined experimental and theoretical study is presented of several ligand addition reactions of the triplet fragments 3Fe(CO) 4 and 3Fe(CO)3 formed upon photolysis of Fe(CO)5. Experimental data are provided for reactions in liquid n-heptane and in supercritical Xe (scXe) and Ar (scAr). Measurement of the temperature dependence of the rate of decay of 1Fe(CO)4 to produce 1Fe(CO)4L (L ) heptane or Xe) shows that these reactions have significant activation energies of 5.2 (±0.2) and 7.1 (±0.5) kcal mol-1 respectively. Nonadiabatic transition state theory is used to predict rate constants for ligand addition, based on density functional theory calculations of singlet and triplet potential energy surfaces. On the basis of these results a new mechanism (spin-crossover followed by ligand addition) is proposed for these spin forbidden reactions that gives good agreement with the new experimental results as well as with earlier gas-phase measurements of some addition rate constants. The theoretical work accounts for the different reaction order observed in the gas phase and in some condensed phase experiments. The reaction of 3Fe(CO)4 with H 2 cannot be easily probed in n-heptane since conversion to 1Fe(CO)4(heptane) dominates. scAr doped with H2 provides a unique environment to monitor this reactionsAr cannot be added to form 1Fe(CO) 4, and H2 addition is observed instead. Again theory accounts for the reactivity and also explains the difference between the very small activation energy measured for H2 addition in the gas phase (Wang, W. et al. J. Am. Chem. Soc. 1996, 118, 8654) and the larger values obtained here for heptane and Xe addition in solution.

Original languageEnglish
Pages (from-to)3583-3592
Number of pages10
JournalJournal of the American Chemical Society
Volume131
Issue number10
DOIs
Publication statusPublished - 18 Mar 2009
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry (all)
  • Biochemistry
  • Colloid and Surface Chemistry

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