The inclusion of anion-cation interactions in calculations of the structure of dibenzenechromium salts by density functional theory

The structures of di(η⁶-benzene)chromium, its isolated radical cation, and model fragments of crystals (C₆H₆)₂ Cr^+·X^-(X = I, Br) were calculated using density functional theory with the PBE functional and an extended split basis set with a relativistic effective core potential. Ignoring (C₆H₆)₂Cr^+· interactions with the counterion was shown to cause some exaggeration of the Cr-C distances in the isolated di(η⁶-benzene)chromium cation compared with the corresponding X-ray structure data.     

Dinuclear and polynuclear transition metal complexes with macrocyclic ligands. 6. New dinuclear copper(ii) complexes with macrocyclic Schiff bases derived from 4-tert-butyl-2,6-diformylphenol

New dinuclear complexes containing Cu^II atoms in the cavity of a macrocyclic Schiff base were prepared by template condensation of 4-tert-butyl-2,6-diformylphenol with 1,3-diaminopropane in the presence of Cu^II trimethylacetate and chloride as well as by extra-ligand exchange. The mononuclear Cu^II complex with two 1,3-diaminopropane molecules can serve as an intermediate in this template synthesis. The reaction of Cu^II trimethylacetate with the unsymmetrical macrocyclic Schiff base synthesized earlier afforded a new dinuclear copper(ii) complex with the amine and imine nitrogen atoms in the coordination sphere. The structures of the new complexes were established by X-ray diffraction analysis and studied by the density functional theory (gradient-corrected PBE functional, TZ2p basis set).     

Electrochemical Probing of Polymethylalumoxane by Pyridine

The dependence of the electrical conductivity of the polymethylalumoxane—pyridine system on the component ratio was studied. The structure and energy effects of the formation of complexes (including charged ones), which arise in interactions between pyridine, reactive fragments of polymethylalumoxane, and the natural concomitants of the latter (the most probable impurities that remain after the synthesis), namely, trimethylaluminum, H₂O, and “simple” alumoxane, [Me₂Al(μ-OAlMe₂)]₂, were calculated by the DFT method. It was found that, in the presence of traces of oxygen-containing donors (alumoxane and/or H₂O), the concentration of ions in solution increased by many orders of magnitude and attained the value observed experimentally. The interaction of pyridine with polymethylalumoxane fragments caused the almost complete replacement of trimethylaluminum, which formed >Al*(Me)(μ-Me)₂AlMe₂ bridges with three-coordinate Al atoms in polymethylalumoxane (Al*), by pyridine. It was shown that an analysis of the dependence of the conductivity of polymethylalumoxane solutions containing “free” trimethylaluminum on the content of pyridine added allowed the concentrations of trimethylaluminum, both free and bound with polymethylalumoxane, to be determined.     

A study of the polymerization of ethylene on Ti(III) monocyclopentadienyl compounds by the density functional theory method

Density functional theory was used to study model ethylene reactions with CpTi^IIIEt⁺A^? (A^? = CH₃B(C₆F₅) ₃ ^? , or B(C₆F₅) ₄ ^? ; A^? can be absent) compounds. The polymerization of ethylene on an isolated CpTiEt⁺ cation is hindered because of equilibrium between the CpTi(C₂H₄)Et⁺ primary complex and the primary product of CpTiBu⁺ insertion. At the same time, the polymerization of ethylene on CpTiEt⁺A^? ion pairs (A^? = CH₃B(C₆F₅) ₃ ^? or B(C₆F₅) ₄ ^? ) is thermodynamically allowed (ΔE from ?26.2 to ?25.6 kcal/mol and ΔG ₂₉₈ from ?10.9 to ?10.4 kcal/mol) and is not related to overcoming substantial energy barriers (ΔE ^# = 8.2?12.3 kcal/mol and ΔG ₂₉₈ ^≠ ) = 7.8?13.3 kcal/mol). The degree of polymerization can be low because of the effective occurrence of polymer chain termination by hydrogen transfer from the polymer chain to the monomer.     

New strategy and methods for constructing artificial macrocyclic anion receptors. Selective binding of tetrahedral oxoanions

A new rational strategy for assembling highly selective neutral macrocyclic anionic receptors proposed by the authors is considered. The strategy includes preliminary theoretical modeling of supramolecular complexes, analysis of synthetic paths for receptor preparation, selection and synthesis of building blocks followed by their cyclocondensation under thermo-dynamic control in the presence of acid corresponding to the target template anion, which provides anion-induced combinatorial selection of the macrocyclic ligand in the emerging dynamic combinatorial library. Analysis of the properties of the obtained anion receptors showed that the number of hydrogen bonds formed between the receptor and the guest anion mainly determines the binding energy. The receptor selectivity for a particular anion is determined by the nature of coordination sites, their geometry in the macrocyclic cavity, and the overall conformation rigidity of the macrocycle. Using the developed strategy and novel synthetic approaches, a large series of highly selective anion receptors with record binding constants (up to 10^p7 L mol^p-1 in both highly and weakly solvating media) was constructed and the structures of the host—guest complexes were studied in detail by both experimental and theoretical methods     

Stable 17-electron manganese complexes in the synthesis of macromolecules

Radical polymerization of methyl methacrylate and styrene in the presence of several cyclopentadienyl manganese dicarbonyl derivatives was studied. The influence of the molecular structure of the complexes on the molecular-weight characteristics of the macromolecules was estimated. Quantum chemical modeling of the initial polymerization step with participation of these complexes was performed.     

Structure of complexes formed by dissolution of palladium diacetate in methanol and chloroform. In situ NMR study

The behavior of palladium diacetate cyclic trimer [Pd(OAc)(2)](3) (1) upon its dissolution in methanol and wet chloroform was studied by (1)H and (13)C NMR including 2D-HSQC and 2D-DOSY techniques. Upon dissolution, trimer 1 reacts with methanol and is completely transformed first into the methoxo complex Pd(3)(μ-OMe)(OAc)(5) (2), which already at -18 °C undergoes a slow exchange of second bridging acetate ligand between the same palladium atoms to form the symmetric dimethoxo complex Pd(3)(μ-OMe)(2)(OAc)(4), the maximum relative concentration of which reaches 20-30 mol % of initial loading trimer 1. Along with the dimethoxo complex, both soluble and insoluble polynuclear palladium clusters are gradually formed at -18 °C, and their total amount reaches up to 60% of the starting Pd(2+) loading. The increase of temperature to 27 °C results in the reduction of palladium(II) to Pd metal by methanol, which is oxidized and transformed into formaldehyde hemiacetal and methyl formate. Upon dissolution in wet chloroform, trimer 1 is reversibly hydrolyzed to the hydroxo complex Pd(3)(μ-OH)(OAc)(5) (10) in ratio 1/10 ≈ 3/1. The temperature decrease and addition of acetic acid shift the equilibrium in this system toward trimer 1, and addition of water shifts it in the opposite direction. Addition of methanol to the equilibrium mixture of 1 and 10 results in the fast exchange of bridging acetate in trimer 1 by the μ-OMe group. Substitution of the μ-OH ligand by μ-OMe in 10 occurs in parallel but more slowly. Complex 2 formed in both cases is more stable in chloroform than in methanol.     

Photochemical reactions of 9-trimethylstannylanthracene in various solvents

9-Trimethylstannylanthracene (1) was synthesized and its photolysis by 365-nm light was studied. In aprotic solvents, the dimerization of 1 involves positions 9 and 10 and yields a head-to-tail dimer. The main route of the photolysis of 1 in alcohols is the cleavage of the C-Sn bond with the formation of anthracene. The quantum yields of the photoreaction and the lifetimes and quantum yields of 1 fluorescence were determined.