The axial ligand effect of oxo-iron porphyrin catalysts. How does chloride compare to thiolate?
We have performed density functional theory calculations on an oxo-iron porphyrin catalyst with chloride as an axial ligand and tested its reactivity toward propene. The reactions proceed via multistate reactivity on competing doublet and quartet spin surfaces. Close-lying epoxidation and hydroxylation mechanisms are identified, whereby in the gas phase the epoxidation reaction is dominant, while in environments with a large dielectric constant the hydroxylation pathways become competitive. By contrast to reactions with thiolate as an axial ligand all low-lying pathways have small ring-closure and rebound barriers, so it is expected that side products and rearrangements will be unlikely with Fe=O(porphyrin)Cl, whereas with Fe=O(porphyrin)SH some side products were predicted. The major differences in the electronic configurations of Fe=O(porphyrin)Cl and Fe=O(porphyrin)SH are due to strong mixing of thiolate orbitals with iron 3d orbitals, a mixing which is much less with chloride as an axial ligand. Predictions of the reactivity of ethylbenzene-h (12) versus ethylbenzene-d (12) are made.
de Visser
Sam P
SP
School of Chemical Engineering and Analytical Science, The University of Manchester, Sackville Street, P.O. Box 88, Manchester M60 1QD, UK. sam.devisser@manchester.ac.uk
D002712:Chlorides / Q000737:chemistry*; D003577:Cytochrome P-450 Enzyme System; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008956:Models, Chemical; D008968:Molecular Conformation; D010100:Oxygen / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*
D002712:Chlorides; D008024:Ligands; D011166:Porphyrins; D003577:Cytochrome P-450 Enzyme System; D007501:Iron; D010100:Oxygen