Oxidative properties of a nonheme Ni(II)(O-2) complex: Reactivity patterns for C-H activation, aromatic hydroxylation and heteroatom oxidation

Manchester Interdisciplinary Biocenter and School of Chemical Engineering and Analytical Science, University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
Chemical Communications (Impact Factor: 6.72). 09/2011; 47(38):10674-6. DOI: 10.1039/c1cc13993b
Source: PubMed

ABSTRACT Density functional theory calculations on the reactivity of a Ni(II)-superoxo complex in C-H bond activation, aromatic hydroxylation and heteroatom oxidation reactions have been explored; the Ni(II)-superoxo complex is able to react with substrates with weak C-H bonds and PPh(3).

  • [Show abstract] [Hide abstract]
    ABSTRACT: Iron–oxygen species, such as iron(IV)-oxo, iron(III)-superoxo, iron(III)-peroxo, and iron(III)-hydroperoxo complexes, are key intermediates often detected in the catalytic cycles of dioxygen activation by heme and nonheme iron enzymes. Our understanding of the chemistry of these key intermediates has improved greatly by studies of the structural and spectroscopic properties and reactivities of their synthetic analogues. One class of biomimetic coordination complexes that has proven to be particularly versatile in studying dioxygen activation by metal complexes is comprised of FeIVO and FeIIIO2(H) complexes of the macrocyclic tetramethylcyclam ligand (TMC, 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). Several recent advances have been made in the synthesis and isolation of new iron–oxygen complexes of this ligand, their structural and spectroscopic characterization, and elucidation of their reactivities in various oxidation reactions. In this review, we summarize the chemistry of the first structurally characterized mononuclear nonheme iron(IV)-oxo complex, in which the FeIVO group was stabilized by the TMC ligand. Complexes with different axial ligands, [FeIV(O)(TMC)(X)]n+, and complexes of other cyclam ligands are discussed as well. Very recently, significant progress has also been reported in the area of other iron–oxygen intermediates, such as iron(III)-superoxo, iron(III)-peroxo, and iron(III)-hydroperoxo complexes bearing the TMC ligand. The present results demonstrate how synthetic and mechanistic developments in biomimetic research can advance our understanding of dioxygen activation occurring in mononuclear nonheme iron enzymes.
    Coordination Chemistry Reviews 01/2013; 257(2):381–393. DOI:10.1016/j.ccr.2012.06.002 · 12.10 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The impact of the macrocyclic ligand on the electronic structure of two LNiO(2) biomimetic adducts, [Ni(12-TMC)O(2) ](+) (12-TMC = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) and [Ni(14-TMC)O(2) ](+) (14-TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), has been inspected by means of difference-dedicated configuration interaction calculations and a valence bond reading of the wavefunction. The system containing the 12-membered macrocyclic ligand has been experimentally described as a side-on nickel(III)-peroxo complex, whereas the 14-membered one has been characterized as an end-on nickel(II)-superoxide. Our results put in evidence the relationship between the steric effect of the macrocyclic ligand, the O(2) coordination mode and the charge transfer extent between the Ni center and the O(2) molecule. The 12-membered macrocyclic ligand favors a side-on coordination, a most efficient overlap between Ni 3d and O(2) π* orbitals and, consequently, a larger charge transfer from LNi fragment to O(2) molecule. The analysis of the ground-state electronic structure shows an enhancement of the peroxide nature of the NiO(2) interaction for [Ni(12-TMC)O(2) ](+) , although a dominant superoxide character is found for both systems. © 2012 Wiley Periodicals, Inc.
    Journal of Computational Chemistry 01/2012; 33(16). DOI:10.1002/jcc.22965 · 3.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Iron(IV)-oxo intermediates are involved in oxidations catalyzed by heme and nonheme iron enzymes, including the cytochromes P450. At the distal site of the heme in P450 Compound I (Fe(IV) -oxo bound to porphyrin radical), the oxo group is involved in several hydrogen-bonding interactions with the protein, but their role in catalysis is currently unknown. In this work, we investigate the effects of hydrogen bonding on the reactivity of high-valent metal-oxo moiety in a nonheme iron biomimetic model complex with trigonal bipyramidal symmetry that has three hydrogen-bond donors directed toward a metal(IV)-oxo group. We show these interactions lower the oxidative power of the oxidant in reactions with dehydroanthracene and cyclohexadiene dramatically as they decrease the strength of the OH bond (BDE(OH) ) in the resulting metal(III)-hydroxo complex. Furthermore, the distal hydrogen-bonding effects cause stereochemical repulsions with the approaching substrate and force a sideways attack rather than a more favorable attack from the top. The calculations, therefore, give important new insights into distal hydrogen bonding, and show that in biomimetic, and, by extension, enzymatic systems, the hydrogen bond may be important for proton-relay mechanisms involved in the formation of the metal-oxo intermediates, but the enzyme pays the price for this by reduced hydrogen atom abstraction ability of the intermediate. Indeed, in nonheme iron enzymes, where no proton relay takes place, there generally is no donating hydrogen bond to the iron(IV)-oxo moiety.
    Chemistry - A European Journal 01/2013; 19(12). DOI:10.1002/chem.201202811 · 5.70 Impact Factor