Selective Ortho‐Hydroxylation–Defluorination of 2‐Fluorophenolates with a Bis(μ‐oxo)dicopper(III) Species

The bis(μ‐oxo)dicopper(III) species [Cu^III₂(μ‐O)₂(m‐XYL^MeAN)]²⁺ ( 1 ) promotes the electrophilic ortho‐hydroxylation–defluorination of 2‐fluorophenolates to give the corresponding catechols, a reaction that is not accomplishable with a (η²:η²‐O₂)dicopper(II) complex. Isotopic labeling studies show that the incoming oxygen atom originates from the bis(μ‐oxo) unit. Ortho‐hydroxylation–defluorination occurs selectively in intramolecular competition with other ortho‐substituents such as chlorine or bromine.     

Dioxygen Activation by a Macrocyclic Copper Complex Leads to a Cu2O2 Core with Unexpected Structure and Reactivity

We report the Cu^I/O₂ chemistry of complexes derived from the macrocylic ligands 14‐TMC (1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane) and 12‐TMC (1,4,7,10‐tetramethyl‐1,4,7,10‐tetraazacyclododecane). While [(14‐TMC)Cu^I]⁺ is unreactive towards dioxygen, the smaller analog [(12‐TMC)Cu^I(CH₃CN)]⁺ reacts with O₂ to give a side‐on bound peroxo‐dicopper(II) species (^SP), confirmed by spectroscopic and computational methods. Intriguingly, 12‐TMC as a N4 donor ligand generates ^SP species, thus in contrast with the previous observation that such species are generated by N2 and N3 ligands. In addition, the reactivity of this macrocyclic side‐on peroxo‐dicopper(II) differs from typical ^SP species, because it reacts only with acid to release H₂O₂, in contrast with the classic reactivity of Cu₂O₂ cores. Kinetics and computations are consistent with a protonation mechanism whereby the TMC acts as a hemilabile ligand and shuttles H⁺ to an isomerized peroxo core.     

Dioxygen Reactivity of Copper(I)/Manganese(II)-Porphyrin Assemblies: Mechanistic Studies and Cooperative Activation of O2

The oxidation of transition metals such as manganese and copper by dioxygen (O₂) is of great interest to chemists and biochemists for fundamental and practical reasons. In this report, the O₂ reactivities of 1:1 and 1:2 mixtures of [(TPP)Mn^II] (1; TPP: Tetraphenylporphyrin) and [(tmpa)Cu^I(MeCN)]⁺ (2; TMPA: Tris(2-pyridylmethyl)amine) in 2-methyltetrahydrofuran (MeTHF) are described. Variable-temperature (−110 °C to room temperature) absorption spectroscopic measurements support that, at low temperature, oxygenation of the (TPP)Mn/Cu mixtures leads to rapid formation of a cupric superoxo intermediate, [(tmpa)Cu^II(O₂^•–)]⁺ (3), independent of the presence of the manganese porphyrin complex (1). Complex 3 subsequently reacts with 1 to form a heterobinuclear μ-peroxo species, [(tmpa)Cu^II–(O₂^2–)–Mn^III(TPP)]⁺ (4; λ_max = 443 nm), which thermally converts to a μ-oxo complex, [(tmpa)Cu^II–O–Mn^III(TPP)]⁺ (5; λ_max = 434 and 466 nm), confirmed by electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy. In the 1:2 (TPP)Mn/Cu mixture, 4 is subsequently attacked by a second equivalent of 3, giving a bis-μ-peroxo species, i.e., [(tmpa)Cu^II−(O₂²⁻)−Mn^IV(TPP)−(O₂²⁻)−Cu^II(tmpa)]²⁺ (7; λ_max = 420 nm and δ_pyrrolic = −44.90 ppm). The final decomposition product of the (TPP)Mn/Cu/O₂ chemistry in MeTHF is [(TPP)Mn^III(MeTHF)₂]⁺ (6), whose X-ray structure is also presented and compared to literature analogs.     

Comprehensive study of pyrido[3,4‐b]pyrazine‐based D–π–a copolymer for efficient polymer solar cells

Two D–π–A copolymers, based on the benzo[1,2‐b:4,5‐b′]‐dithiophene (BDT) as a donor unit and benzo‐quinoxaline (BQ) or pyrido‐quinoxaline (PQ) analog as an acceptor (PBDT‐TBQ and PBDT‐TPQ), were designed and synthesized as a p‐type material for bulk heterojunction (BHJ) photovoltaic cells. When compared with the PBDT‐TBQ polymer, PBDT‐TPQ exhibits stronger intramolecular charge transfer, showing a broad absorption coverage at the red region and narrower optical bandgap of 1.69 eV with a relatively low‐lying HOMO energy level at ?5.24 eV. The experimental data show that the exciton dissociation efficiency of PBDT‐TPQ:PC₇₁BM blend is better than that in the PBDT‐TBQ:PC₇₁BM blend, which can explain that the IPCE spectra of the PBDT‐TPQ‐based solar cell were higher than that of the PBDT‐TBQ‐based solar cell. The maximum efficiency of PBDT‐TPQ‐based device reaches 4.40% which is much higher than 2.45% of PBDT‐TBQ, indicating that PQ unit is a promising electron‐acceptor moiety for BHJ solar cells. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1822–1833     

Reaktionen der Digalliumverbindung R2Ga–GaR2 [R = CH(SiMe3)2] mit Wasser und Carbonsäuren – Synthese von μ‐Hydroxo‐μ‐carboxylatodigallium‐Verbindungen unter Erhalt der Ga–Ga‐Bindungen

Treatment of the digallium compound R₂Ga–GaR₂ [ 1 , R = CH(SiMe₃)₂] with a broad variety of functionalized carboxylic acids in the presence of water yielded μ‐hydroxo‐μ‐carboxylatodigallium compounds ( 2 – 10 ) containing intact Ga–Ga bonds in high to moderate yields. The compounds form dimeric formula units in which the unsupported Ga–Ga bonds are bridged by two hydroxo and two carboxylato ligands. Each gallium atom is terminally coordinated by a bulky alkyl group. NMR spectroscopy revealed mixtures of two isomeric compounds in solution in all cases. The second component may show a different bridging mode with each Ga–Ga bond bridged by a bidentate carboxylato ligand to form Ga₂O₂C five‐membered heterocycles.     

Picolinamides as Effective Ligands for Copper‐Catalysed Aryl Ether Formation: Structure–Activity Relationships,Substrate Scope and Mechanistic Investigations

The use of picolinic acid amide derivatives as an effective family of bidentate ligands for copper‐catalysed aryl ether synthesis is reported. A fluorine‐substituted ligand gave good results in the synthesis of a wide range of aryl ethers. Even bulky phenols, known to be very challenging substrates, were shown to react with aryl iodides with excellent yields using these ligands. At the end of the reaction, the first examples of end‐of‐life Cu species were isolated and identified as Cu^II complexes with several of the anionic ligands tested. A preliminary mechanistic investigation is reported that suggests that the substituents on the ligands might have a crucial role in determining the redox properties of the metal centre and, consequently, its efficacy in the coupling process. An understanding of these effects is important for the development of new efficient and tunable ligands for copper‐based chemistry.     

Mononuclear Manganese–Peroxo and Bis(μ‐oxo)dimanganese Complexes Bearing a Common N‐Methylated Macrocyclic Ligand

Mononuclear Mn^III–peroxo and dinuclear bis(μ‐oxo)Mn^III₂ complexes that bear a common macrocyclic ligand were synthesized by controlling the concentration of the starting Mn^II complex in the reaction of H₂O₂ (i.e., a Mn^III–peroxo complex at a low concentration (≤1 mM ) and a bis(μ‐oxo)Mn^III₂ complex at a high concentration (≥30 mM )). These intermediates were successfully characterized by various physicochemical methods such as UV–visible spectroscopy, ESI‐MS, resonance Raman, and X‐ray analysis. The structural and spectroscopic characterization combined with density functional theory (DFT) calculations demonstrated unambiguously that the peroxo ligand is bound in a side‐on fashion in the Mn^III–peroxo complex and the Mn₂O₂ diamond core is in the bis(μ‐oxo)Mn^III₂ complex. The reactivity of these intermediates was investigated in electrophilic and nucleophilic reactions, in which only the Mn^III–peroxo complex showed a nucleophilic reactivity in the deformylation of aldehydes.     

Natural Compounds against Neurodegenerative Diseases: Molecular Characterization of the Interaction of Catechins from Green Tea with Aβ1–42, PrP106–126, and Ataxin‐3 Oligomers

By combining NMR spectroscopy, transmission electron microscopy, and circular dichroism we have identified the structural determinants involved in the interaction of green tea catechins with Aβ1–42, PrP106–126, and ataxin‐3 oligomers. The data allow the elucidation of their mechanism of action, showing that the flavan‐3‐ol unit of catechins is essential for interaction. At the same time, the gallate moiety, when present, seems to increase the affinity for the target proteins. These results provide important information for the rational design of new compounds with anti‐amyloidogenic activity and/or molecular tools for the specific targeting of amyloid aggregates in vivo.     

Structure–activity relationship of N‐heterocyclic carbene–Pd(II)–imidazole complexes in Suzuki–Miyaura coupling between 4‐methoxyphenyl chloride and phenylboronic acid

A series of N‐heterocyclic carbene–PdCl₂–imidazole [NHC–Pd(II)–Im] complexes were synthesized and the structure of most of them was unambiguously determined by X‐ray single‐crystal diffraction. The structure–activity relationship of these complexes was investigated for the Suzuki–Miyaura coupling between 4‐methoxyphenyl chloride and phenylboronic acid, and the effect of the NHCs and Im moieties were fully discussed. The sterically hindered IPr‐based complex showed the highest catalytic activity. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and Structures of d10–d10 M2(μ‐dppm)2 Complexes with Sensitive Metal–Metal Distances in Response to the Binding of Sigma Donors

Diphosphine‐bridged dicopper(I) acetate complexes [Cu₂(μ‐dppm)₂(μ‐OAc)]X ( 2 X; X^? = , ) and [Cu₂(μ‐dppm)₂(μ‐OAc)(MeCN)]X ( 4 X) were prepared and the structures of 2 (PF₆ ) and 4 (PF₆ ) determined by X‐ray crystallography. The ground‐state geometries of [Cu₂(μ‐dppm)₂(μ‐OAc)]⁺ and [Cu₂(μ‐dppm)₂(μ‐OAc)(L)]⁺ (L = py, MeCN, THF, acetone, MeOH) were also obtained using density functional theory (DFT). The increased Cu – Cu distances found experimentally and theoretically by comparing the structures of cation [Cu₂(μ‐dppm)₂(μ‐OAc)]⁺ and its derivatives [Cu₂(μ‐dppm)₂(μ‐OAc)(L)]⁺ reflect the binding of various sigma donors (L). When using [Cu₂(μ‐dppm)₂(μ‐OAc)]⁺ as a structure sensor, the electron‐donating strength of a sigma donor can be quantitatively expressed as a DFT‐calculated Cu – Cu distance with the relative strength in the order py > MeCN > THF > acetone > MeOH, as determined.     

Dichlorodinickel(I) Complexes with μ2-CO or μ2-CS Bridges and Trimethylphosphane Ligands: Homologous Composition,but Different Frameworks

High ligand mobility is shown by the coordinatively unsaturated nickel(I ) compound 1 with a short Ni–Ni distance and an asymmetric CO bridge. The thio homologue 2 contains the novel (thiocarbonyl)trimethylphosphorane bridging ligand, which sits like a “stork's nest” on top of the roof-shaped dinuclear complex. In contrast to 1 , complex 2 does not show fluctional behavior and can be methylated without decomposition. X=Cl, Me.     

Conformational Selection in Glycomimetics: Human Galectin‐1 Only Recognizes syn‐Ψ‐Type Conformations of β‐1,3‐Linked Lactose and Its C‐Glycosyl Derivative

The human lectin galectin‐1 (hGal‐1) translates sugar signals, that is, β‐galactosides, into effects on the level of cells, for example, growth regulation, and has become a model for studying binding of biopharmaceutically relevant derivatives. Bound‐state conformations of Galβ‐C‐(1→3)‐Glcβ‐OMe ( 1 ) and its βGal‐(1→3)‐βGlc‐OMe disaccharide parent compound were studied by using NMR spectroscopy (transferred (TR)‐NOESY data), assisted by docking experiments and molecular dynamics (MD) simulations. The molecular recognition process involves a conformational selection event. Although free C‐glycoside access four distinct conformers in solution, hGal‐1 recognizes shape of a local minimum of compound 1 , the syn‐Φ/syn‐Ψ conformer, not the structure at global minimum. MD simulations were run to explain, in structural terms, the observed geometry of the complex.     

Controlling Metal–Ligand–Metal Oxidation State Combinations by Ancillary Ligand (L) Variation in the Redox Systems [L2Ru(μ‐boptz)RuL2]n,boptz=3,6‐bis(2‐oxidophenyl)‐1,2,4,5‐tetrazine,and L=acetylacetonate, 2,2′‐bipyridine,or 2‐phenylazopyridine

The new compounds [(acac)₂Ru(μ‐boptz)Ru(acac)₂] ( 1 ), [(bpy)₂Ru(μ‐boptz)Ru(bpy)₂](ClO₄)₂ ( 2 ‐(ClO₄)₂), and [(pap)₂Ru(μ‐boptz)Ru(pap)₂](ClO₄)₂ ( 3 ‐(ClO₄)₂) were obtained from 3,6‐bis(2‐hydroxyphenyl)‐1,2,4,5‐tetrazine (H₂boptz), the crystal structure analysis of which is reported. Compound 1 contains two antiferromagnetically coupled (J=?36.7 cm^?1) Ru^III centers. We have investigated the role of both the donor and acceptor functions containing the boptz^2? bridging ligand in combination with the electronically different ancillary ligands (donating acac^?, moderately π‐accepting bpy, and strongly π‐accepting pap; acac=acetylacetonate, bpy=2,2′‐bipyridine pap=2‐phenylazopyridine) by using cyclic voltammetry, spectroelectrochemistry and electron paramagnetic resonance (EPR) spectroscopy for several in situ accessible redox states. We found that metal–ligand–metal oxidation state combinations remain invariant to ancillary ligand change in some instances; however, three isoelectronic paramagnetic cores Ru(μ‐boptz)Ru showed remarkable differences. The excellent tolerance of the bpy co ‐ ligand for both Ru^III and Ru^II is demonstrated by the adoption of the mixed ‐ valent form in [L₂Ru(μ‐boptz)RuL₂]³⁺, L=bpy, whereas the corresponding system with pap stabilizes the Ru^II states to yield a phenoxyl radical ligand and the compound with L=acac^? contains two Ru^III centers connected by a tetrazine radical‐anion bridge.     

Enantio‐ and Site‐Selective α‐Fluorination of N‐Acyl 3,5‐Dimethylpyrazoles Catalyzed by Chiral π–CuII Complexes

Catalytic enantioselective α‐fluorination reactions of carbonyl compounds are among the most powerful and efficient synthetic methods for constructing optically active α‐fluorinated carbonyl compounds. Nevertheless, α‐fluorination of α‐nonbranched carboxylic acid derivatives is still a big challenge because of relatively high pK_a values of their α‐hydrogen atoms and difficulty of subsequent synthetic transformation without epimerization. Herein we show that chiral copper(II) complexes of 3‐(2‐naphthyl)‐l ‐alanine‐derived amides are highly effective catalysts for the enantio‐ and site‐selective α‐fluorination of N‐(α‐arylacetyl) and N‐(α‐alkylacetyl) 3,5‐dimethylpyrazoles. The substrate scope of the transformation is very broad (25 examples including a quaternary α‐fluorinated α‐amino acid derivative). α‐Fluorinated products were converted into the corresponding esters, secondary amides, tertiary amides, ketones, and alcohols with almost no epimerization in high yield.     

The heterometallic cadmium–silver complex cis‐bis[dicyanidoargentato(I)‐κN]bis(5,5′‐dimethyl‐2,2′‐bipyridyl‐κ2N,N′)cadmium(II) monohydrate

In the title complex, [Ag₂Cd(CN)₄(C₁₂H₁₂N₂)₂]·H₂O or cis‐[Cd{Ag(CN)₂}₂(5,5′‐dmbpy)₂]·H₂O, where 5,5′‐dmbpy is 5,5′‐dimethyl‐2,2′‐bipyridyl, the asymmetric unit consists of a discrete neutral [Cd{Ag(CN)₂}₂(5,5′‐dmbpy)₂] unit and a solvent water molecule. The Cd^II cation is coordinated by two bidentate chelate 5,5′‐dmbpy ligands and two monodentate [Ag^I(CN)₂]⁻ anions, which are in a cis arrangement around the Cd^II cation, leading to an octahedral CdN₆ geometry. The overall structure is stabilized by a combination of intermolecular hydrogen bonding, and Ag^I...Ag^I and π–π interactions, forming a three‐dimensional supramolecular network.