Iron N-Heterocyclic Carbenes (NHCs) have been successfully utilized in various catalytic transformations including C-C bond formation and hydrogenation. Both the nature of the active species in many of these catalytic reactions and a fundamental understanding of iron-NHC bonding and electronic structure in iron-NHC complexes remains poorly defined. Therefore, detailed electronic structure and bonding studies of well-defined iron-NHC complexes that vary in oxidation state, coordination number, and geometry are vital to the full understanding of these systems. Using a variety of inorganic spectroscopic methods including magnetic circular dichroism and M�ssbauer, combined with density functional theory calculations, a series of four-coordinate tetrahedral iron(II)-NHC complexes of the type (NHC)2FeCl2 and three-coordinate distorted trigonal planar iron(II)-NHC complexes of the type (NHC)Fe(R)2 (R = benzyl, CH2SiMe3) have been investigated. Through direct evaluation of the ligand-field transition energies and charge transfer transitions present in these complexes combined with DFT and TD-DFT investigations, these studies provide critical insight into the donor and acceptor abilities of NHC ligands in iron(II) complexes. Specific properties investigated include the effect of NHC backbone substitutions on iron(II)-NHC electronic structure and bonding, ancillary ligand effects on iron(II)-NHC bonding and the ligand field strengths of NHCs relative to other common ligands employed in iron catalysis (e.g. phosphines, amines).

Electronic structure and bonding in iron(II)-NHC complexes

248th National Meeting (2014)

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