Ruthenium carborane complexes in the controlled radical polymerization of methyl methacrylate

New initiators based on closo-and exo-nido-ruthenacarboranes with phosphine and diphosphine ligands were proposed as chain growth regulators. They allow conducting the controlled synthesis of poly(methyl methacrylate) under radical initiation conditions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 85–89, January, 2006.     

Cationic methyl complexes of rhodium(III): synthesis, structure, and some reactions

Cationic methyl complex of rhodium(III), trans-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (1) is prepared by interaction of trans-[Rh(Acac)(PPh₃)₂(CH₃)I] with AgBPh₄ in acetonitrile. Cationic methyl complexes of rhodium(III), cis-[Rh(Acac)(PPh₃)₂ (CH₃)(CH₃CN)][BPh₄] (2) and cis-[Rh(BA)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (3) (Acac, BA are acetylacetonate and benzoylacetonate, respectively), are obtained by CH₃I oxidative addition to rhodium(I) complexes [Rh(Acac)(PPh₃)₂] and [Rh(BA)(PPh₃)₂] in acetonitrile in the presence of NaBPh₄. Complexes 2 and 3 react readily with NH₃ at room temperature to form cis-[Rh(Acac)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (4) and cis-[Rh(BA)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (5), respectively. Complexes 1-5 were characterized by elemental analysis, ¹H and ³¹P{¹H} NMR spectra. Complexes 1, 2, 3 and 4 were characterized by X-ray diffraction analysis. Complexes 2 and 3 in solutions (CH₂Cl₂, CHCl₃) are presented as mixtures of cis-(PPh₃)₂ isomers involved into a fluxional process. Complex 2 on heating in acetonitrile is converted into trans-isomer 1. In parallel with that isomerization, reductive elimination of methyl group with formation of [CH₃PPh₃][BPh₄] takes place. Replacement of CH₃CN in complexes 1 and 2 by anion I⁻ yields in both cases the neutral complex trans-[Rh(Acac)(PPh₃)₂(CH₃)I]. Strong trans influence of CH₃ ligand manifests itself in the elongation (in solid) and labilization (in solution) of rhodium-acetonitrile nitrogen bond.     

On the reactions of methyl radicals with TiO2 nanoparticles and granular powders immersed in aqueous solutions

Methyl radicals react with TiO(2) nanoparticles (NPs) immersed in aqueous solutions to form transients in which the methyls are covalently bound to the particles. The rate constant for this reaction approaches the diffusion-controlled limit and increases somewhat with the number of methyls bound to the particle. The transients decompose to yield ethane. Thus, formally the particles "catalyse" the dimerization of the radicals, a reaction that is diffusion-controlled. Rutile powders behave similarly to the TiO(2) NPs whereas the mechanism for the decomposition of the transients formed in the analogous reaction of the radicals with anatase powders differs. These results are of importance as alkyl radicals are formed near the surface of TiO(2) in a variety of important photocatalytic processes. The results imply that the reactions of alkyl radicals with TiO(2) have to be considered in these processes.     

Manganese(II) complexes with diethylamine in aqueous solutions

Interaction between MnCl₂ and diethylamine (DEA) in aqueous solutions has been studied by UV, IR, and EPR spectroscopy as part of the design and research program on models of natural photosystems. The composition of the precipitate for comparable concentrations of reagents and solute oxygen has been investigated. Mn(II) was found to be oxidized with oxygen to give MnO₂·H₂O as a precipitate. In the solution over the precipitate, Mn(III) complexes with DEA are formed; the complex molecule has four and six amine molecules in the coordination sphere.     

Protonation of nitrilotris(methanephosphonic) acid and its salts in aqueous solutions

The reactions of aqueous solutions of nitrilotris(methanephosphonic) acid and its salts, and also of 1-hydroxyethane-1,1-diphosphonic acid and tetraethylammonium salt of 1-aminoethanephosphonic acids with hydrochloric acid at 25°C were studied by the dilatometric method. The results were discussed in the context of the idea on the existence of the betaine form of an acid molecule and its anions and the existence of proton chelates of aminophosphonic compounds in solutions.     

Reactivity and regiochemical behavior in the solvolysis reactions of (2,2-difluorocyclopropyl)methyl tosylates

The rate constants for acetolysis of (2,2-difluorocyclopropyl)methyl tosylate, and (2,2-difluoro-3-methylcyclopropyl)methyl tosylate at 92 °C and of 1-(2,2-difluorocyclopropyl)ethyl tosylate at 42 °C are reported and the reactivities and regiochemistries of ring opening of these systems are discussed and compared with expectations based on computational results. The results are discussed in terms of the use of (2,2-difluorocyclopropyl)methyl systems as mechanistic probes.     

Interpolymer complexes of poly(acrylic acid) with poly(2-hydroxyethyl acrylate) in aqueous solutions

Complexes formed from poly(acrylic acid) and poly(2-hydroxyethyl acrylate) were studied in aqueous solutions by viscometric, turbidimetric, FTIR spectroscopic, and thermogravimetric analysis methods. The formation of interpolymer complexes stabilized by hydrogen bonds was observed. It was found that the compositions of these interpolymer complexes are strongly dependent on the concentration of polymers, the order of mixing the solutions, and the pH. It was demonstrated that the complexation ability of poly(2-hydroxyethyl acrylate) is relatively low compared to other known nonionic water-soluble polymers. However, it can be significantly increased via hydrophobic modification of the poly(acrylic acid) using cetyl pyridinium bromide.     

On oxygen diffusion in poly(methyl methacrylate) films

ESR spectroscopy has been used to follow the kinetics of decay of radicals produced by UV-radiation in PMMA films upon exposure to oxygen in the temperature range 160-210 K. In the same films and at the same conditions, decay kinetics of phenanthrene phosphorescence has been studied at 180-220 K. Both types of the experiments give the same values for diffusion coefficients of oxygen in PMMA. Thus, from the oxygen diffusion standpoint, the sites of the radical stabilization and phenanthrene molecule localization in the polymer matrix do not differ.     

The interaction of poly(methacrylate) radicals with diphenyldiacetylenes

The free radical polymerization of methyl methacrylate (MMA) in the presence of p,p′- disubstituted diphenylbutadiynes was studied. Both the rate and degree of polymerization are somewhat lowered by the presence of the diynes, but the propagating radicals were stabilized giving clear ESR signals of the interacted polyMMA radicals at the polymerization temperature of 70°C. The magnitude of the interaction depended on the electron density of the diynes; in the cases of diphenylbutadiyne and dimethoxycarbonyldiphenylbutadiyne, the intoraction was more enhanced showing ESR signals with smaller spectra widths and increasing the number of radicals with the polymerization time, while in the cases of electron donor-substituted diynes the interaction was weaker and the radical concentration remained constant during the polymerization. These systems are considered to be examples of the stabilization of transient radicals by the direct interaction of radicals with additives without formation or breaking of chemical bonds. No diacetylenic group was found in the polyMMA obtained. © 1994 John Wiley & Sons, Inc.     

Mechanism of reaction of alkyl radicals with (Ni(II)L)2+ complexes in aqueous solutions

The reactions of methyl radicals, CH(3), with the macrocyclic complexes Ni(II)L(1-5) (L(1-5) = cyclam derivatives, vide infra) and Ni(II)edta in aqueous solutions were studied. Methyl radicals react with all these nickel complexes, forming intermediates with Ni(III)-C sigma-bonds. The L(m)Ni(III)-CH(3) complexes are formed in equilibria processes with relatively fast forward rate constants of k(f) > 1 x 10(8) M(-1) s(-1) (except in the case of NiL(2)-trans I cyclam, where the reaction is slower). In all cases the decomposition of the transient complexes occurs via the homolytic cleavage of the metal-carbon sigma-bond. When the homolysis is relatively slow, an isomerisation process of the transient is also observed with the exception of NiL(2), where no isomerisation was observed. The results suggest that the strength of the Ni(III)-CH(3)sigma-bond is mainly affected by steric hindrance.     

Kinetics and mechanism of the reactions of hexaaqua rhodium (III) with sulphur (IV) in aqueous medium

An O-bonded sulphito complex, Rh(OH₂)₅(OSO₂H)²⁺, is reversibly formed in the stoppedflow time scale when Rh(OH₂) ₆ ³⁺ and SO₂/HSO ₃ ⁻ buffer (1 <pH< 3) are allowed to react. For Rh(OH₂)₅OH₂₊+ SO₂ □ Rh(OH₂)₅(OSO₂H)²⁺ (k₁/k_-1), k₁ = (2.2 ±0.2) × 10³ dm³ mol⁻¹ s⁻¹, k₋1 = 0.58 ±0.16 s⁻¹ (25°C,I = 0.5 mol dm⁻³). The protonated O-sulphito complex is a moderate acid (K _d = 3 × 10⁻⁴ mol dm⁻³, 25°C, I= 0.5 mol dm⁻³). This complex undergoes (O, O) chelation by the bound bisulphite withk= 1.4 × 10⁻³ s⁻¹ (31°C) to Rh(OH₂)₄(O₂SO)⁺ and the chelated sulphito complex takes up another HSO ₃ ⁻ in a fast equilibrium step to yield Rh(OH₂)₃(O₂SO)(OSO₂H) which further undergoes intramolecular ligand isomerisation to the S-bonded sulphito complex: Rh(OH₂)₃(O₂SO)(OSO₂)^- → Rh(OH₂)₃(O₂SO)(SO₃)⁻ (k _iso = 3 × 10⁻⁴ s⁻¹, 31°C). A dinuclear (μ-O, O) sulphite-bridged complex, Na₄[Rh₂(μ-OH)₂(OH)₂(μ-OS(O)O)(O₂SO)(SO₃) (OH₂)]5H₂O with (O, O) chelated and S-bonded sulphites has been isolated and characterized. This complex is sparingly soluble in water and most organic solvents and very stable to acid-catalysed decomposition     

The interaction of carbon-centered radicals with copper(I) and copper(II) complexes*

Abstract

Although alkylcopper(I) reagents are widespread, compounds containing alkyl ligands on Cu^II or Cu^III are much less common. Such complexes, however, are generated as transient species when carbon-center radicals add to Cu^I or Cu^II complexes, respectively, and appear to be involved in several copper-catalyzed organic transformations. A few organocopper(II) and organocopper(III) complexes were found sufficiently robust to allow isolation and full characterization. This article reviews the reactivity of carbon-centered radicals with Cu^I and Cu^II ions, both in aqueous and non-aqueous environments, with focus on the importance of the resulting organocopper species on atom transfer radical polymerization and on copper-catalyzed radical termination.     

Formation of poly(ethylene glycol) inclusion complexes in aqueous solutions of mixed cyclodextrins

Even though the addition of modified cyclodextrins (modified CDs) accelerates the precipitation in aqueous solutions of poly(ethylene glycol) (PEG) and α-cyclodextrin (α-CD) the final amount of formed solid complex remains unchanged, with no significant presence of modified CDs detected by MALDI-TOF mass spectrometry. Thus unsuitability of kinetic turbidity measurements for determination of binding parameters was confirmed. On the other hand, theoretical calculations based on a model of a chain of freely accessible binding sites demonstrated that the results do not necessarily contradict the finding that individual modified CD molecules can thread onto PEG chains with the efficiency comparable to that of natural (unmodified) α-CD.     

Redox reactions of V(III) and Cr(III)picolinate complexes in aqueous solutions

Reactions of e_aq⁻, H-atoms, OH, (CH₃)₂COH, and CO₂⁻ radicals with V(III)picolinate and Cr(III)picolinate have been studied by the pulse radiolysis technique. The spectra of V(II)picolinate, V(IV)picolinate, Cr(II)picolinate, OH adduct of Cr(III)picolinate and Cr(IV)picolinate have been obtained and the rate constants of the reactions of various radicals with V(III) and Cr(III)picolinate have been determined. The implications of these results to the chemical decontamination of nuclear reactor systems are discussed.     

Inclusion complexes of spin-labeled indoles with cyclodextrins in aqueous solutions

Guest-host complexes of β- and γ-cyclodextrins (CDs) with two spin-labeled indole derivatives having the same molecular weights but different structures were studied by EPR spectroscopy in aqueous solutions and semiempirical quantum-chemical calculations of these systems were carried out. In the presence of CD the polarity of the NO group environment decreases and the rotational correlation time (τ) of guest molecules increases. Both indole derivatives form 1 : 1 complexes with γ-CD, the binding constants of the complexes being different more than twice. Simulation of EPR spectra made it possible to determine the indole ring orientation relative to the plane of the host molecule (at angles in the range 30–60°) and the rotational diffusion coefficients of the complexes, which corresponded to the hydrodynamic volume of one γ-CD molecule. In contrast to the complexes with γ-CD the rotational correlation times, τ, of the complexes with β-CD correspond to a hydrodynamic volume which much exceeds the volume of a single β-CD molecule. The complexes with β-CD are also characterized by more hydrophobic environment for guest molecules and absence of spin exchange with Ni²⁺ ions in the aqueous solution. There results are consistent with a dimeric structure of β-CD in the complex and with the orientation of the long axis of the guest molecule along the dimer axis. The energies and geometric parameters were calculated for all complexes by the PM3 method with a conventional set of parameters. The optimized energetically stable structures of the 1 : 1 complexes with γ-CD and of the 1 : 2 complexes with β-CD are consistent with experimental data. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1139–1147, May, 2005.     

Conductance behavior of some tris(ethylenediamine)cobalt(III) complexes and their ion association in aqueous solutions

The conductance behavior of some tris(ethylenediamine)cobalt(III) complexes was studied in dilute aqueous solutions at 25°C to investigate the ion-pair formation. The thermodynamic formation constants of the ion pairs [Co(en)₃]³⁺·X^– are 28 (chloride), 28 (bromide), 19 (nitrate), and 15 (perchlorate). These values were compared with theoretical values calculated by using Bjerrum's theory of ion association. The formation constant of [Co(en)₃]³⁺·Cl^– was larger than that obtained from the spectrophotometric measurement in solutions containing perchlorate ion. This difference in the formation constants was explained by considering the contribution of ion association of the complex cation with perchlorate ion.     

Generation of phenylmethylketyl radicals in aqueous solutions and study of their transformation

Acetophenone and its intermediates formed upon the first electron transfer are studied by laser photoemission and traditional electrochemistry. It is shown that the intermediate reduction is affected by competition of the reactions of the formed radical-anions oxidation and their subsequent transformation to secondary products that are rapidly reduced at the electrode. From the comparison of the data obtained by the laser photoemission method and electrochemical measurements a conclusion was drawn that the product is a metastable complex (associate) of the radical-anion with water molecule; its formation rate constant is rather low (～6 × 10³ M^?1 s^?1). It was also concluded that bulk radical reactions dominate in aprotic media at moderate cathodic potentials; the acetophenone radical-anion is reduced at E ≤ ?1.9 V (SCE). This conclusion agrees with the results of the acetophenone preparative electrolysis in DMFA, where marked yield of pinacon was observed at the potentials of limiting current of the 1st reduction wave, while the stage of 2nd electron transfer occurred at E ≤ ?2.3 V (SCE).