Synthesis, Characterization, and Spectroscopic Studies of 2,6-Dimethylpyridyl-Linked Cu(I)-CNC Complexes: The Electronic Influence of Aryl Wingtips on Copper Centers.

Six new Cu(I) complexes containing pincer ligands of the type 2,6-bis(3-alkyl/arylimidazol-2-ylidene) methylpyridine I(R/Ar) , where R = trifluoroethyl (TFE) and R' = 4-CF, 4-NO, 4-CN, 4-H, and 4-CH, have been synthesized. These complexes, namely, [Cu(I(TFE))]PF, ; [Cu(IAr ]PF, ; [Cu(IAr )]PF, ; [Cu(IAr ]PF, ; [Cu(IAr )](PF), ; and [Cu(IAr )](PF), , were fully characterized by H, C, and HMBC NMR spectroscopy, elemental analysis, electrochemical studies, and single-crystal X-ray crystallography. The crystallographic data revealed different structures and copper nuclearities for the complexes bearing aryl wingtips with electron-withdrawing (, , and ) and electron-donating ( and ) substituents.

pH Changes That Induce an Axial Ligand Effect on Nonheme Iron(IV) Oxo Complexes with an Appended Aminopropyl Functionality.

Nonheme iron enzymes often utilize a high-valent iron(IV) oxo species for the biosynthesis of natural products, but their high reactivity often precludes structural and functional studies of these complexes. In this work, a combined experimental and computational study is presented on a biomimetic nonheme iron(IV) oxo complex bearing an aminopyridine macrocyclic ligand and its reactivity toward olefin epoxidation upon changes in the identity and coordination ability of the axial ligand. Herein, we show a dramatic effect of the pH on the oxygen-atom-transfer (OAT) reaction with substrates.

Computational studies of DNA base repair mechanisms by nonheme iron dioxygenases: selective epoxidation and hydroxylation pathways.

DNA base repair mechanisms of alkylated DNA bases is an important reaction in chemical biology and particularly in the human body. It is typically catalyzed by an α-ketoglutarate-dependent nonheme iron dioxygenase named the AlkB repair enzyme. In this work we report a detailed computational study into the structure and reactivity of AlkB repair enzymes with alkylated DNA bases.

Synthesis, characterization, and photoluminescent studies of three-coordinate Cu(i)-NHC complexes bearing unsymmetrically-substituted dipyridylamine ligands.

A series of heteroleptic three-coordinate Cu(i) complexes bearing monodentate N-heterocyclic carbene (NHC) ligands of the type 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) and 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr), and bidentate N-donor ligands of the type unsymmetrically-substituted dimethyl dipyridylamine (MeHdpa) and bis(mesityl)biazanaphthenequinone (mesBIAN) have been synthesized. The complexes [Cu(IPr)(3,4'-MeHdpa)]PF, 1; [Cu(IPr)(3,5'-MeHdpa)]PF, 2; [Cu(IPr)(3,6'-MeHdpa)]PF, 3; [Cu(IPr)(mesBIAN)]PF, 6; [Cu(SIPr)(3,4'-MeHdpa)]PF, 7; [Cu(SIPr)(3,5'-MeHdpa)]PF, 8; and [Cu(SIPr)(3,3'-MeHdpa)]PF, 11 have been characterized by H and C NMR spectroscopies, elemental analysis, cyclic voltammetry, and photophysical studies in solid and solution phase. Single crystal X-ray structures were obtained for all complexes except 11.

C-X (X = N, O) Cross-Coupling Reactions Catalyzed by Copper-Pincer Bis(N-Heterocyclic Carbene) Complexes.

Over the last two decades, N-heterocyclic carbene (NHC)-copper catalysts have received considerable attention in organic synthesis. Despite the popularity of copper complexes containing monodentate NHC ligands and recent development of poly(NHC) platforms, their application in C-C and C-heteroatom cross-coupling reactions has been limited. Recently, we reported an air-assisted Sonogashira-type cross-coupling catalyzed by well-defined cationic copper-pincer bis(NHC) complexes.

Square-planar Co(iii) in {O} coordination: large ZFS and reactivity with ROS.

Oxidation of distorted square-planar perfluoropinacolate Co compound [CoII(pinF)2]2-, 1, to [CoIII(pinF)2]1-, 2, is reported. Rigidly square-planar 2 has an intermediate-spin, S = 1, ground state and very large zero-field splitting (ZFS) with D = 67.2 cm-1; |E| = 18.

Cu(I) Complexes of Pincer Pyridine-Based N-Heterocyclic Carbenes with Small Wingtip Substituents: Synthesis and Structural and Spectroscopic Studies.

Six new Cu(I) complexes with pincer N-heterocyclic carbene (NHC) ligands of the type 2,6-bis(3-alkylimidazol-2-ylidene)pyridine, I(R), and 2,6-bis(3-alkylimidazol-2-ylidene)methylpyridine, I(R), where R = Me, Et, and Pr have been synthesized using Cu precursors and bis(imidazolium) salts. All of these compounds, namely, [Cu(IMe)](PF), 1; [Cu(IEt)](PF), 2; [Cu(IPr)](PF), 3; [Cu(IMe)](PF), 4; [Cu(IEt)](PF), 5; and [Cu(IPr)](PF), 6, have been characterized by H and C NMR spectroscopies, elemental analysis, solution conductivity, and electrochemical studies. Single crystal X-ray structures were obtained for all complexes except 1.

Structural and electronic properties of old and new A2[M(pin(F))2] complexes.

Seven new homoleptic complexes of the form A2[M(pin(F))2] have been synthesized with the dodecafluoropinacolate (pin(F))(2-) ligand, namely (Me4N)2[Fe(pin(F))2], 1; (Me4N)2[Co(pin(F))2], 2; ((n)Bu4N)2[Co(pin(F))2], 3; {K(DME)2}2[Ni(pin(F))2], 4; (Me4N)2[Ni(pin(F))2], 5; {K(DME)2}2[Cu(pin(F))2], 7; and (Me4N)2[Cu(pin(F))2], 8. In addition, the previously reported complexes K2[Cu(pin(F))2], 6, and K2[Zn(pin(F))2], 9, are characterized in much greater detail in this work. These nine compounds have been characterized by UV-vis spectroscopy, cyclic voltammetry, elemental analysis, and for paramagnetic compounds, Evans method magnetic susceptibility.

K⋅⋅⋅F/O interactions bridge copper(I) fluorinated alkoxide complexes and facilitate dioxygen activation.

Seven E[Cu(OR)2] copper(I) complexes (E = K(+), {K(18C6)}(+) (18C6 = [18]crown-6), or Ph4P(+); R = C4F9, CPhMe(F)2, and CMeMe(F)2) have been prepared and their reactivity with O2 studied. The K[Cu(OR)2] species react with O2 in a copper-concentration-dependent manner such that 2:1 and 3:1 Cu/O2 adducts are observed manometrically at -78 °C. Analogous reactivity with O2 is not observed with the {K(18C6)}(+) or Ph4P(+) derivatives.

Factors that control catalytic two- versus four-electron reduction of dioxygen by copper complexes.

The selective two-electron reduction of O(2) by one-electron reductants such as decamethylferrocene (Fc*) and octamethylferrocene (Me(8)Fc) is efficiently catalyzed by a binuclear Cu(II) complex [Cu(II)(2)(LO)(OH)](2+) (D1) {LO is a binucleating ligand with copper-bridging phenolate moiety} in the presence of trifluoroacetic acid (HOTF) in acetone. The protonation of the hydroxide group of [Cu(II)(2)(LO)(OH)](2+) with HOTF to produce [Cu(II)(2)(LO)(OTF)](2+) (D1-OTF) makes it possible for this to be reduced by 2 equiv of Fc* via a two-step electron-transfer sequence. Reactions of the fully reduced complex [Cu(I)(2)(LO)](+) (D3) with O(2) in the presence of HOTF led to the low-temperature detection of the absorption spectra due to the peroxo complex [Cu(II)(2)(LO)(OO)] (D) and the protonated hydroperoxo complex [Cu(II)(2)(LO)(OOH)](2+) (D4).

Regioselectivity of aliphatic versus aromatic hydroxylation by a nonheme iron(II)-superoxo complex.

Many enzymes in nature utilize molecular oxygen on an iron center for the catalysis of substrate hydroxylation. In recent years, great progress has been made in understanding the function and properties of iron(IV)-oxo complexes; however, little is known about the reactivity of iron(II)-superoxo intermediates in substrate activation. It has been proposed recently that iron(II)-superoxo intermediates take part as hydrogen abstraction species in the catalytic cycles of nonheme iron enzymes.

Electron-transfer reduction of dinuclear copper peroxo and bis-μ-oxo complexes leading to the catalytic four-electron reduction of dioxygen to water.

The four-electron reduction of dioxygen by decamethylferrocene (Fc*) to water is efficiently catalyzed by a binuclear copper(II) complex (1) and a mononuclear copper(II) complex (2) in the presence of trifluoroacetic acid in acetone at 298 K. Fast electron transfer from Fc* to 1 and 2 affords the corresponding Cu(I) complexes, which react at low temperature (193 K) with dioxygen to afford the η(2):η(2)-peroxo dicopper(II) (3) and bis-μ-oxo dicopper(III) (4) intermediates, respectively. The rate constants for electron transfer from Fc* and octamethylferrocene (Me(8)Fc) to 1 as well as electron transfer from Fc* and Me(8)Fc to 3 were determined at various temperatures, leading to activation enthalpies and entropies.

Oxidative properties of a nonheme Ni(II)(O2) complex: Reactivity patterns for C-H activation, aromatic hydroxylation and heteroatom oxidation.

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).

The axial ligand effect on aliphatic and aromatic hydroxylation by non-heme iron(IV)-oxo biomimetic complexes.

Iron(IV)-oxo heme cation radicals are active species in enzymes and biomimetic model complexes. They are potent oxidants in oxygen atom transfer reactions, but the reactivity is strongly dependent on the ligand system of the iron(IV)-oxo group and in particular the nature of the ligand trans to the oxo group (the axial ligand). To find out what effect the axial ligand has on the reactivity of non-heme iron(IV)-oxo species, we have performed a series of density functional theory (DFT) calculations on aliphatic and aromatic hydroxylation reactions by using [Fe(IV)=O(TMC)(L)](n+) (TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, and L=acetonitrile or chloride).

Manganese substituted Compound I of cytochrome P450 biomimetics: a comparative reactivity study of Mn(V)-oxo versus Mn(IV)-oxo species.

Manganese-oxo porphyrins have been well studied as biomimetic models of cytochromes P450 and are known to be able to catalyze substrate hydroxylation reactions. Recent experimental studies [J.Y.

Effect of porphyrin ligands on the regioselective dehydrogenation versus epoxidation of olefins by oxoiron(IV) mimics of cytochrome P450.

The cytochromes P450 are versatile enzymes involved in various catalytic oxidation reactions, such as hydroxylation, epoxidation and dehydrogenation. In this work, we present combined experimental and theoretical studies on the change of regioselectivity in cyclohexadiene oxidation (i.e.

Fundamental differences of substrate hydroxylation by high-valent iron(IV)-oxo models of cytochrome P450.

An Iron(IV)-oxo heme(+*) complex (Compound I, Cpd I) is the proposed active species of heme enzymes such as the cytochromes P450 and is elusive; therefore, biomimetic studies on active site mimics give valuable insight into the fundamental properties of heme active species. In this work we present density functional theory (DFT) calculations on substrate hydroxylation by a Compound I mimic [Fe(IV)=O(Por(+*))Cl] and its one-electron reduced form [Fe(IV)=O(Por)Cl](-). Thus, recent experimental studies showed that [Fe(IV)=O(Por)Cl](-) is able to react with substrates via hydride transfer reactions [Jeong, Y.

How does the axial ligand of cytochrome P450 biomimetics influence the regioselectivity of aliphatic versus aromatic hydroxylation?

The catalytic activity of high-valent iron-oxo active species of heme enzymes is known to be dependent on the nature of the axial ligand trans to the iron-oxo group. In a similar fashion, experimental studies on iron-oxo porphyrin biomimetic systems have shown a significant axial ligand effect on ethylbenzene hydroxylation, with an axial acetonitrile ligand leading to phenyl hydroxylation products and an axial chloride anion giving predominantly benzyl hydroxylation products. To elucidate the fundamental factors that distinguish this regioselectivity reversal in iron-oxo porphyrin catalysis, we have performed a series of density functional theory calculations on the hydroxylation of ethylbenzene by [Fe(IV)=O(Por(+.