Oksana V. Nesterova

Catalytic behaviour of a novel Fe(III) Schiff base complex in the mild oxidation of cyclohexane

The complex [FeIII(HL)Cl2(DMF)]Cl·DMF (1) was synthesized by reaction of Fe(III) chloride with a dimethylformamide solution of the Schiff base aminoalcohol HL (2-[(E)-{[2-(piperazin-1-yl)ethyl]imino}methyl]phenol) and characterized by single crystal X-ray diffraction analysis, thermogravimetry and spectroscopic methods. The catalytic investigations disclosed a marked activity of 1 towards oxidation of cyclohexane with hydrogen peroxide, under mild conditions, with yields based on cyclohexane up to 37% and TONs (turnover numbers) up to ca. 900. Kinetic experiments and selectivity parameters led to the conclusion that hydroxyl radicals are active (attacking C–H bonds) species in the studied catalytic reaction. Kinetic and UV/Vis spectrometry data revealed a complex nature of the processes occurring in the catalytic system, including the transformation of 1 into catalytically active species.

Direct synthesis of an heterometallic {MnII3CrIII4} wheel by decomposition of Reineckes salt

A new heterometallic Mn/Cr molecular wheel complex has been synthesized using zerovalent manganese, Reineckes salt, ammonium thiocyanate and triethanolamine (H(3)tea) as starting materials. The compound [Mn(3)Cr(4)(NCS)(6)(Htea)(6)] (1) has been characterized in terms of its electrochemical, IR and EPR spectroscopic as well as its magnetic properties. The magnetic susceptibility and magnetization data were treated simultaneously during the optimization routine and resulted in J(Mn-Cr) = +0.43 cm(-1), J(Cr-Cr) = -4.75 cm(-1), J(Mn-Mn) = +1.78 cm(-1), g(eff) = 1.878 with the ground state S = 15/2.

How to force a classical chelating ligand to a metal non-chelating bridge: the observation of a rare coordination mode of diethanolamine in the 1D complex {[Cu2(Piv)4(H3tBuDea)](Piv)}n

The novel chain coordination polymer {[Cu2(Piv)4(H3tBuDea)](Piv)}n (1) has been prepared through the self-assembly reaction of copper(II) nitrate with pivalic acid (HPiv) and N-tert-butyldiethanolamine (H2tBuDea) in acetonitrile solution. Crystallographic analysis revealed the extremely rare non-chelating bridging coordination mode of diethanolamine ligand in 1, observed for the first time in transition metal complexes, as well as in complexes of diethanolamine having a non-coordinating aliphatic group at the N atom. Possible reasons for such a coordination and analysis of the main coordination modes of diethanolamine-based ligands are discussed. Variable-temperature (1.8–300 K) magnetic susceptibility measurements showed that 1 represents a rare example of dicopper(II) tetracarboxylate that is a diamagnetic solid at room temperature. This behaviour is compared with literature examples and discussed on the basis of DFT calculations. Furthermore, 1 acts as an efficient catalyst for the mild hydrocarboxylation of linear and cyclic C5–C8 alkanes into the corresponding carboxylic acids.

Specific features of the temperature characteristics of electrical conductivity and photoconductivity of polymer composites containing Cu(II)/Cr(III) heterometallic complexes

The temperature characteristics of the electric current and the photocurrent in films of composites based on electrically neutral poly(vinyl butyral) with additions of Cu(II)/Cr(III) heterometallic cation-anion complexes are investigated. The electrical conductivity and photoconductivity of the polymer composite films in the visible optical range increase with a decrease in the distance between the metal centers in the complexes and upon introduction of acceptor additions of the C60 fullerene into the composition of the polymer binder and increase exponentially with increasing temperature. The activation energy of electrical conduction and photoconduction exceeds 1 eV and depends weakly on the strength of the external electric field. The temperature characteristics of the electrical conductivity and photoconductivity of the materials under investigation are explained by the specific features of trapping of charge carriers at the interface between particles of the heterometallic complex and the polymer binder.

Stereoselective oxidation of alkanes with m-CPBA as an oxidant and cobalt complex with isoindole-based ligands as catalysts

Two complexes with isoindole-core ligands of general formula [M{C6H4C(NH2)NC(ONCMe2)2}2](NO3)2 (M = Co for 1 and M = Ni for 2) were studied as catalysts for the mild stereoselective alkane oxidation with m-chloroperbenzoic acid (m-CPBA) as an oxidant and cis-1,2-dimethylcyclohexane (cis-1,2-DMCH) as a main model substrate. Complex 1 disclosed a pronounced activity, with high retention of stereoconfiguration of substrates (>98% for cis-1,2-DMCH) and highest cis/trans ratio of tertiary alcohols (products) of 56, under mild conditions. The best achieved yields of tertiary cis-alcohols were of 13.7 and 50.5%, based on the substrate (cis-1,2-DMCH) and the oxidant (m-CPBA) respectively. Kinetic experiments, high bond and stereoselectivity parameters, kinetic isotope effect of 7.2(2) in the oxidation of cyclohexane, and incorporation of 18O from H218O support the involvement of CoIVO high-valent metal–oxo intermediates as main C–H attacking species.

A three-dimensional framework of bis[tris(ethylenediamine)zinc] tetraiodocadmate diiodide assisted by N-H...I hydrogen bonds.

The title salt, [Zn(C(2)N(2)H(8))(3)](2)[CdI(4)]I(2), conventionally abbreviated [Zn(en)(3)](2)[CdI(4)]I(2), where en is ethylenediamine, contains discrete [Zn(en)(3)](2+) cations and [CdI(4)](2-) anions with distorted octahedral and nearly tetrahedral geometries, respectively, as well as uncoordinated I(-) ions. The cation and the free I(-) anion lie on twofold rotation axes and the [CdI(4)](2-) anion lies on a -4 axis in the space group I-42d. The structure exhibits numerous weak inter-ionic hydrogen bonds of two types, viz. N-H...I(-)(free ion) and N-H...I([CdI(4)](2-)), which support the resulting three-dimensional framework.

Tris(2,2′-bipyridine)­copper(II) penta­cyanido­nitro­soferrate(II) methanol disolvate monohydrate

The title complex [Cu(C10H8N2)3][Fe(CN)5(NO)]·2CH3OH·H2O, consists of discrete [Cu(bpy)3]2+ cations (bpy is 2,2′-bipyridine), [Fe(CN)5NO]2− anions and solvent molecules of crystallization (two methanol molecules and one water molecules per asymmetric unit). The CuII ion adopts a distorted octahedral environment, coordinated by six N atoms from three bpy ligands. The cation charge is balanced by a nitroprusside counter-anion, which has a slightly distorted octahedral coordination geometry. In the crystal, anions and solvent molecules are involved in O—H⋯N and O—H⋯O hydrogen bonds, which form chains along [100]. The cations are located between these chains.

Diammine(2,2′-bipyridine)­bis(thio­cyan­ato­-κN)cobalt(III) diamminetetra­kis(thio­cyanato­-κN)chromate(III) aceto­nitrile disolvate

The new heterometallic title complex, [Co(NCS)2(C10H8N2)(NH3)2][Cr(NCS)4(NH3)2]·2CH3CN, has been prepared using the open-air reaction of cobalt powder, Reineckes salt and 2,2′-bipyridine (dpy) in acetonitrile. The crystal structure consists of discrete cationic [Co(NCS)2(NH3)2(dpy)]+ and anionic [Cr(NCS)4(NH3)2]− building blocks, both with 2 symmetry, and acetonitrile solvent molecules, which are linked together by N—H⋯N hydrogen bonds, forming extended supramolecular chains. Furthermore, N—H⋯S, C—H⋯S and C—H⋯N hydrogen bonds interlink neighbouring chains into a three-dimensional framework. The Co atom is in an elongated octahedral coordination environment with two N atoms from the dpy ligands and two NCS-groups in the equatorial plane and with two NH3 molecules at the axial positions. The CrIII ion is octahedraly coordinated by two NH3 molecules at the axial positions and four NCS-groups in the equatorial plane. Intensity statistics indicated non-merohedral twinning with the twin matrix [100; 00; 0]. The refined ratio of the twin components is 0.530 (1):0.470 (1).

Specific features of the internal photoelectric effect of the Cu(II)/Fe(III) oxalate complex with ethylenediamine in an insulating polymer film

The electrical and photoconductive properties of films of the composites based on poly(vinyl alcohol) with additions of the (NH4)[Cu(en)2Fe(C2O4)3] · 2DMSO complex, which forms polycrystalline structures in the films, have been studied. The increment of the conduction current under exposure to light is independent of the application of the voltage during illumination. The kinetics of increase and relaxation of the photoinduced conductivity does not depend on the voltage and light intensity (in the ranges under investigation). The photoinduced conductivity of the films decreases in the external magnetic field. The kinetics of change in the photocurrent after turning the magnetic field on and off is similar to the kinetics of its increase and relaxation after turning light on and off. The specific features of the internal photoelectric effect and the appearance of the memory effect under exposure to light have been attributed to deep energy traps sensitive to the magnetic field.

Copper(II) Complexes with Bulky N-Substituted Diethanolamines: High-Field Electron Paramagnetic Resonance, Magnetic, and Catalytic Studies in Oxidative Cyclohexane Amidation

The novel coordination compounds [Cu2(H tBuDea)2(OAc)2] (1) and [Cu2(H nBuDea)2Cl2]· nH2O (2) have been prepared through the reaction of the respective copper(II) salts with N- tert-butyldiethanolamine (H2 tBuDea, for 1) or N-butyldiethanolamine (H2 nBuDea, for 2) in methanol solution. Crystallographic analysis reveals that, in spite of the common binuclear {Cu2(μ-O)2} core, the supramolecular structures of the complexes are drastically different. In 1 binuclear molecules are linked together by H-bonds into 1D chains, while in 2 the neighboring pairs of binuclear molecules are H-bonded, forming tetranuclear aggregates. Variable-temperature (1.8-300 K) magnetic susceptibility measurements of 1 and 2 show a dominant antiferromagnetic behavior. Both complexes are also studied by HF-EPR spectroscopy. While the interaction between Cu(II) centers in 1 can be described by a single coupling constant J = 130.1(3) cm-1 (using H = JS1 S2), the crystallographically different {Cu2(μ-O)2} pairs in 2 are expected exchange from ferro- to antiferromagnetic behavior (with J ranging from -32 to 110 cm-1, according to DFT calculations). Complexes 1 and 2 act as catalysts in the amidation of cyclohexane with benzamide, employing tBuOO tBu as oxidant. The maximum achieved conversion of benzamide (20%, after 24 h reaction time) was observed in the 1/ tBuOO tBu system. In the cases of tBuOO(O)CPh or tBuOOH oxidants, no significant amidation product was observed, while for tBuOO(O)CPh, the oxidative dehydrogenation of cyclohexane occurred, giving cyclohexene, to afford the allylic ester (cyclohex-2-en-1-yl benzoate) as the main reaction product.