Three-coordinate Iron Complexes Research Articles

Electronic Structure and Reactivity of Three-Coordinate Iron Complexes

[Reaction: see text]. The identity and oxidation state of the metal in a coordination compound are typically thought to be the most important determinants of its reactivity. However, the coordination number (the number of bonds to the metal) can be equally influential. This Account describes iron complexes with a coordination number of only three, which differ greatly from iron complexes with octahedral (six-coordinate) geometries with respect to their magnetism, electronic structure, preference for ligands, and reactivity. Three-coordinate complexes with a trigonal-planar geometry are accessible using bulky, anionic, bidentate ligands (beta-diketiminates) that steer a monodentate ligand into the plane of their two nitrogen donors. This strategy has led to a variety of three-coordinate iron complexes in which iron is in the +1, +2, and +3 oxidation states. Systematic studies on the electronic structures of these complexes have been useful in interpreting their properties. The iron ions are generally high spin, with singly occupied orbitals available for pi interactions with ligands. Trends in sigma-bonding show that iron(II) complexes favor electronegative ligands (O, N donors) over electropositive ligands (hydride). The combination of electrostatic sigma-bonding and the availability of pi-interactions stabilizes iron(II) fluoride and oxo complexes. The same factors destabilize iron(II) hydride complexes, which are reactive enough to add the hydrogen atom to unsaturated organic molecules and to take part in radical reactions. Iron(I) complexes use strong pi-backbonding to transfer charge from iron into coordinated alkynes and N 2, whereas iron(III) accepts charge from a pi-donating imido ligand. Though the imidoiron(III) complex is stabilized by pi-bonding in the trigonal-planar geometry, addition of pyridine as a fourth donor weakens the pi-bonding, which enables abstraction of H atoms from hydrocarbons. The unusual bonding and reactivity patterns of three-coordinate iron compounds may lead to new catalysts for oxidation and reduction reactions and may be used by nature in transient intermediates of nitrogenase enzymes.

Low-coordinate iron complexes as synthetic models of nitrogenase

Three-coordinate iron sites are potentially important intermediates in the reduction of dinitrogen by the enzyme nitrogenase, but synthetic work to outline the behavior of three-coordinate iron complexes is in its infancy. Recent work shows that bulky diketiminate ligands give a general route to three-coordinate iron complexes with a variety of third ligands. The low coordination number leads to exciting new reactions in which N—N bonds are weakened or broken. Such complexes show great promise for evaluating the ability of low-coordinate iron to perform bond cleavage reactions akin to the individual steps of the nitrogenase system.Key words: nitrogenase, three-coordinate iron, diketiminate, N–N cleavage.

Three-coordinate iron complexes: x-ray structural characterization of the iron amide-bridged dimers [Fe(NR2)2]2 (R = SiMe3, C6H5) and the adduct Fe[N(SiMe3)2]2(THF) and determination of the association energy of the monomer Fe{N(SiMe3)2}2 in solution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThree-coordinate iron complexes: x-ray structural characterization of the iron amide-bridged dimers [Fe(NR2)2]2 (R = SiMe3, C6H5) and the adduct Fe[N(SiMe3)2]2(THF) and determination of the association energy of the monomer Fe{N(SiMe3)2}2 in solutionMarilyn M. Olmstead, Philip P. Power, and Steven C. ShonerCite this: Inorg. Chem. 1991, 30, 11, 2547–2551Publication Date (Print):May 1, 1991Publication History Published online1 May 2002Published inissue 1 May 1991https://doi.org/10.1021/ic00011a017RIGHTS & PERMISSIONSArticle Views3075Altmetric-Citations178LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (595 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts