Aminophenol dioxygenases (APDO) are mononuclear nonheme iron enzymes that utilize dioxygen (O2) to catalyze the conversion of o-aminophenols to 2-picolinic acid derivatives in metabolic pathways. ...This study describes the synthesis and O2 reactivity of two synthetic models of substrate-bound APDO: FeII(TpMe2)(tBu2APH) (1) and FeII(TpMe2)(tBuAPH) (2), where TpMe2 = hydrotris(3,5-dimethylpyrazole-1-yl)borate, tBu2APH = 4,6-di-tert-butyl-2-aminophenolate, and tBuAPH2 = 4-tert-butyl-2-aminophenolate. Both Fe(II) complexes behave as functional APDO mimics, as exposure to O2 results in oxidative CC bond cleavage of the o-aminophenolate ligand. The ring-cleaved products undergo spontaneous cyclization to give substituted 2-picolinic acids, as verified by 1H NMR spectroscopy, mass spectrometry, and X-ray crystallography. Reaction of the APDO models with O2 at low temperature reveals multiple intermediates, which were probed with UV–vis absorption, electron paramagnetic resonance (EPR), Mössbauer (MB), and resonance Raman (rRaman) spectroscopies. The most stable intermediate at −70 °C in THF exhibits multiple isotopically-sensitive features in rRaman samples prepared with 16O2 and 18O2, confirming incorporation of O2-derived atom(s) into its molecular structure. Insights into the geometric structures, electronic properties, and spectroscopic features of the observed intermediates were obtained from density functional theory (DFT) calculations. Although functional APDO models have been previously reported, this is the first time that an oxygenated ligand-based radical has been detected and spectroscopically characterized in the ring-cleaving mechanism of a relevant synthetic system.
Synopsis: Nonheme iron(II) complexes behave as functional models of aminophenol dioxygenases by reacting with O2 to yield oxygenated ring-cleaved products. The mechanism is explored by monitoring the reaction at reduced temperature to observe and trap reactive intermediates. Characterization with multiple spectroscopic techniques revealed that the most stable intermediate contains O2-derived atoms in its molecular structure. Display omitted
•Functional nonheme iron models of aminophenol dioxygenases are prepared and structually characterized.•The models replicate the enzymatic reaction by yielding oxidized ring-cleaved products in the presence of O2.•Intermediates of relevance to enzymatic catalysis are interrogated with multiple spectroscopic techniques.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Treating U(IV) imido compounds with benzonitrile or 4-cyanopyridine results in unusual products of cycloaddition. 1H and 11B NMR, infrared, and electronic absorption spectroscopic analysis provides ...evidence of tetravalent uranium compounds, while X-ray crystallography confirmed molecular structures. Previous examples of actinide imidos treated with nitriles resulted in cyclometallated products; thus, the compounds reported represent divergent chemistry in that an κ1-amidinate ligand is formed through 2π + 2π-cycloaddition and 2π + 2π-cycloreversion.
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Treating U(IV) imido compounds, Tp∗2U(N-p-methoxyphenyl) (2-OMe) and Tp∗2U(N-pTol) (2-pTol), with benzonitrile or 4-cyanopyridine results in unusual products of multiple bond metathesis (2π + 2π-cycloaddition and 2π + 2π-cycloreversion). 1H and 11B NMR, infrared, and electronic absorption spectroscopic analyses provides evidence of tetravalent uranium compounds, while X-ray crystallography confirmed molecular structures to be Tp∗2UNC(N-pOMePh)pyr (3-py), Tp∗2UNC(N-pOMePh)Ph (3-Ph), Tp∗2UNC(N-pTol)pyr (4-py), Tp∗2UNC(N-pTol)Ph (4-Ph), Tp∗2UNC(N-pOMePh)p-CNPh (5-OMe), and Tp∗2UNC(N-pTol)p-CNPh (5-Tol). Previous examples of actinide imidos treated with nitriles resulted in cyclometallated products; thus, the compounds reported represent divergent chemistry in that an κ1-amidinate ligand is formed through 2π + 2π-cycloaddition and 2π + 2π-cycloreversion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Recent advances in the synthesis of water‐soluble homoscorpionates of the tris(pyrazol‐1‐yl)methane type as well as of their water‐soluble metal complexes are reviewed. Moreover, the application of ...these tris(pyrazol‐1‐yl)methane metal complexes as catalysts for the oxidative functionalization of inexpensive and abundant alkanes to value‐added products and other industrially significant reactions is addressed. We also focus on the main biological (antiproliferative and antimicrobial) applications of such C‐scorpionate‐type complexes.
Water‐soluble carbon homoscorpionates and their coordination chemistry are reviewed. Moreover, the application of the resulting water‐soluble tris(pyrazol‐1‐yl)methane metal complexes as catalysts for C–C bond formation and oxidative functionalization as well as their use as antiproliferative and antimicrobial agents are addressed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The bonding situation of Ag(I)CO complexes having a Scorpionate ligand directly attached to the transition metal has been analyzed in detail by means of relativistic density functional theory ...calculations. To this end, different experimentally characterized complexes together with other representative species have been considered to rationalize the observed shift of the corresponding ν(CO) stretching frequencies and the influence of the substituents in the Scorpionate ligand. With the help of the energy decomposition analysis method combined with the natural orbital for chemical valence it is found that the main contribution to the bonding comes from the electrostatic attractions between the LAg(I) and CO fragments. Despite that, the LAg → CO π‐backdonation is also significant in these species as well as in related LCu(I)CO complexes.
This work computationally explores the bonding situation of silver(I)‐carbonyl complexes having a Scorpionate ligand. By means of the energy decomposition analysis, the crucial role of electrostatic interactions and π‐backdonation is revealed.
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The ferrocene‐chelating heteroscorpionate complex (fc(PPh2){BH{(3,5‐Me)2pz}2})PdMe {(fcP,B)PdMe, fc = 1,1′‐ferrocenediyl, pz = pyrazole} catalyzes the addition polymerization of norbornene and ...norbornene derivatives upon oxidation with AcFcBArF {acetyl ferrocenium tetrakis(3,5‐bis(trifluoromethyl)phenyl)borate}. In situ reduction of (fcP,B)PdMeBArF in the presence of a substituted norbornene results in significant decrease of catalytic activity. Addition of one equivalent of oxidant restores the activity.
A cationic ferrocene‐chelating heteroscorpionate methylpalladium complex catalyzes the addition polymerization of norbornene and norbornene derivatives. Redox switchable polymerization of these monomers was also accomplished.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The group 11 metal adducts HB{3‐(CF3),5‐(CH3)Pz}3M(C2H4) (M = Au, Ag, and Cu; Pz = pyrazolyl) have been synthesized via a metathesis process using HB{3‐(CF3),5‐(CH3)Pz}3Na and CF3SO3Cu, CF3SO3Ag, ...AuCl and ethylene. The related HB{3‐(CF3),5‐(Ph)Pz}3Ag(C2H4) has also been synthesized using HB{3‐(CF3),5‐(Ph)Pz}3Na(THF), CF3SO3Ag and ethylene. These group 11 metal ethylene complexes are white solids and form colorless crystals. They have been characterized by NMR spectroscopy and X‐ray crystallography. The gold‐ethylene adduct HB{3‐(CF3),5‐(CH3)Pz}3Au(C2H4) shows large upfield NMR shifts of the ethylene proton and carbon signals relative to the corresponding peaks of the free ethylene, indicating relatively high Au→ethylene backbonding. NMR chemical shift data suggest that the silver complexes of both the tris(pyrazolyl)borate ligands HB{3‐(CF3),5‐(CH3)Pz}3– and HB{3‐(CF3),5‐(Ph)Pz}3– exhibit the weakest interaction with ethylene as compared to the respective copper and gold complexes. X‐ray crystal structures reveal that the gold atom in HB{3‐(CF3),5‐(CH3)Pz}3Au(C2H4) binds to scorpionate in κ2‐fashion while the related silver adduct features a κ3‐bonded scorpionate. HB{3‐(CF3),5‐(CH3)Pz}3Cu(C2H4) has a scorpionate that binds to copper with two short Cu–N bonds and one long Cu–N distance.
Partially fluorinated scorpionate HB{3‐(CF3),5‐(CH3)Pz}3– allows the stabilization of molecules with gold(I), silver(I) and copper(I) ethylene adducts. Related adducts supported by HB{3‐(CF3),5‐(CH3)Pz}3– are also included for comparisons. Notable differences exist in scorpionate modes of coordination and ethylene carbon chemical shift values.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The structures of metal complexes of two classes of multitopic, “third generation” poly(pyrazolyl)methane ligands, ligands specifically functionalized at the non‐coordinating “back” position, are ...discussed. For tris(pyrazolyl)methane based (pz)3C–CH2–O–CH2nC6H6–n (n = 2, 3, 4 and 6, pz = pyrazolyl ring) ligands, three bonding modes are observed depending on the metal, counterion and solvent: a) the κ3 (tripodal) mode, where all three pyrazolyl rings are coordinated to one metal; b) the κ2‐κ0 mode, with only two pyrazolyl rings bonded to a metallic center while the third is not involved in a donor bond; and c) in a κ2‐κ1 fashion, in which the tris(pyrazolyl)methane unit acts as a bridge between two metals. For bis(pyrazolyl)methane based CH2–O–CH2–CH(pz)2nC6H6–n ligands, the main structural arrangement is a mononuclear cationic unit in which two arms of the ligand bond a single silver(I) cation in a tetradentate fashion, giving rise to 16‐ or 17‐member metallacyclic structures.
Multitopic poly(pyrazolyl)methane ligands form metal complexes that show a variety of bonding modes and intricate overall structures.
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A surprisingly simple approach led to the synthesis of a molecular calcium hydride. Reaction of a calcium amide with phenylsilane gives clean conversion into the hydride that crystallizes as a dimer ...(see structure).
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The importance of scorpionate ligands in modern coordination chemistry continues to increase, because of their outstanding versatility, tunability and user‐friendliness. Herein, we provide a short ...overview of recent developments in the classes of scorpionate ligands, derived from pyrazoles, triazoles, imidazoles, oxazolines, thioimidazoles and other similar systems, followed by an in‐depth discussion of a new type of robust and tunable scorpionate ligand, tris(2‐pyridyl)borates. The structure and synthesis of tris(2‐pyridyl)borate (Tpyb) ligands are discussed, and key features of coordination of Tpyb ligands with metal ions, as well as supramolecular crystal packing, transmetallation and applications in metallo‐supramolecular polymer chemistry are addressed.
An overview of the different classes of scorpionate ligands is provided, and an in‐depth discussion of a new type of robust and tunable ligand, the tris(2‐pyridyl)borates. The structure and synthesis of the ligands, key features of coordination with metal ions, the supramolecular crystal packing, transmetallation and applications in metallo‐supramolecular polymer chemistry are addressed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this brief review we focus on a few examples of how a family of homo‐ and heteroscorpionate ligands allow us to examine how changes in reactivity, structure, or physical/chemical properties around ...biologically interesting N2X coordinated metal centers vary as a function of donor atom, charge, hydrophobicity, hydrogen bonding, etc., in a way previously unavailable. Such a family of ligands is the bioinorganic chemists answer to site‐directed mutagenesis. Here we focus on two bioinorganic examples i.e. models for molybdoenzymes and zinc metalloproteins.
A family of heteroscorpionate ligands of the form N2X is presented where X can be interchanged between a thiolate sulfur, a pyrazole nitrogen, or a carboxylate, alkoxy or phenoxy oxygen in a series of isostructural isoelectronic metal complexes gives the bioinorganic chemist the ability to do the equivalent of “site directed mutagenesis”.
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