Serguei Fomine

The Glaser reaction mechanism. A DFT study

Abstract A detailed mechanism for the Hey modification of the Glaser oxidative coupling of terminal acetylenes has been formulated based on DFT calculations. The mechanism includes Cu(I)/Cu(III)/Cu(II)/Cu(I) catalytic cycle and explains the dioxygen molecule activation mechanism by Cu(I) species to give water molecule as final product of dioxygen reduction. The key step of the reaction mechanism is the oxidation of Cu acetylide by molecular oxygen to form dicopper-dioxo complex with [Cu2(μ-O2)]2+ core. Relatively low activation energies found for the reaction steps support the viability of the formulated mechanism.

Polymers from coumarines: 4. Design and synthesis of novel hyperbranched and comb-like coumarin-containing polymers

Abstract Novel monomers containing coumarin groups [2-(7-Cumarinyloxy)Oethoxy]dimethyl terephthalate and [6-(3-carboxy)coumarinyl] diacetylhydroquinone were synthesized and polymerized by high temperature polycondensation to give hyperbranched and comb-like coumarin-containing polymers. All polymers were completely soluble in chlorinated aliphatic hydrocarbons and showed M n in the range of 2000–50000 and gave film of good optical quality on casting from solution. All polymers except one were amorphous with T g in the range of 100–230°C and thermostability of 370–415°C. All polymers were found to be blue emitters emitting light in the range 450–492 nm.

Molecular modeling of the olefin metathesis by tungsten(0) carbene complexes

Abstract Density functional and second-order Moller–Plesset theory were used to model W(0) carbene mediated homogeneous metathesis reaction of propylene. The calculations show that the rate determining step of the metathesis is the initiation. After the initiation has been completed the rate determining step becomes dissociation of olefin–metallocarbene complex. The low stereoselectivity of the olefin metathesis reaction is due to the close matching of activation energies for cis and trans isomer formation and the fast cis–trans isomerization caused by the catalysts. The non-productive olefin metathesis reaction always dominates the reaction mixture owing to its very low activation energy. The electronic structure of metal carbene olefin complexes can be described as a combination of donor–acceptor interactions between HOMO of the olefin and LUMO of metal carbene located at carbene carbon on the one hand, and the Dewar, Chatt and Duncanson back donation scheme on the other.

Multiconfigurational character of the ground states of polycyclic aromatic hydrocarbons. A systematic study

AbstractA systematic study of the electronic structure of polycyclic hydrocarbons from naphthalene to a system containing 80 fused benzene has been carried out. Geometries were optimized for closed shell singlet, open shell singlet, triplet and multiplet states at B3LYP/cc-pVDZ level of theory, D1 (second order Møller–Plesset) and D1 (second-order approximate coupled-cluster) diagnostics have been calculated for studied molecules. Complete active space self-consistent field (10,10)/6-31G(d) single point energy calculations have been carried out for all optimized structures. Multireference character of the ground state becomes important when the number of atoms in the polycyclic hydrocarbon exceeds 40–50. At this point, D1 diagnostics reaches 0.04–0.05 and the squared configuration interaction expansion coefficient for dominant configuration drops to about 0.6. However, only for the three largest systems predominantly polyradicalic ground states have been detected. All other polycyclic hydrocarbons showing significant multiconfigurational character of singlet ground state have only two dominant configurations which are closed shell singlet and doubly excited singlet, respectively. Thus, small polycyclic hydrocarbons have mostly single reference singlet ground state, the medium size systems have notably multireference ground state (singlet or triplet) with only moderate polyradicalic character. The ground state of largest systems is singlet polyradical. FigureᅟGround states of polycyclic aromatic hydrocarbons

Tubular Aggregates of Cyclic Oligothiophenes. A Theoretical Study

The geometries of neutral, mono-, and dioxidized tubular aggregates of cyclo[8]thiophenes containing up to 5 repeating units were fully optimized at the MPWB1K/3-21G* level of theory. Calculated interplane distances between macrocycles were found to be close to 3.1 A for neutral and charged aggregates. The binding energies between macrocycles in neutral intermediates were in the range of 40-45 kcal/mol, increasing for monocations and dropping strongly for dicationic species due to electrostatic repulsion between polarons. It was established that there exists a noticeable interaction between pi-orbitals of individual macrocycles in tubular aggregates as follows from decreasing of the band gap with a number of repeating units in aggregates and the polaron delocalization toward tube axes in oxidized species. A polaron pair is the most stable dicationic state for all studied molecules according to the calculations. A singlet polaron pair is more stable than a triplet one. The energy difference between singlet and triplet states is growing smaller with the size of the system, becoming zero for the pentamer corresponding to a completely dissociated bipolaron.

Construction of simplified models to simulate estrogenic disruptions by esters of 4-hydroxy benzoic acid (parabens)

Four parabens (methyl, n-butyl, benzyl and isobutylparaben) were theoretically studied in order to evaluate their estrogenic activity through simplified models. The experimental structure of the human estrogen receptor ligand-binding domain in complex with 17beta-estradiol was used as the starting point to construct the models. The complex between 17beta-estradiol and three fragments of the estrogenic receptor (Arg, Glu and His), resulted in a reasonable simplified model of interaction. The replacement of 17-beta-estradiol by parabens was evaluated by conformational analyses and interaction energy calculations at BHandHLYP/cc-PVTZ(-f)+ level of theory. According with the calculated interaction energies, methylparaben is the paraben with higher estrogenic activity, which is in agreement with experimental studies of extraction and quantification of parabens in tumors. The antibacterial activity of parabens was also explored considering the formation of potassium salts in the phenolic OH groups. From the obtained relative energy values, methylparaben is the most active preservative.

Remarkable enhancement of reactivity of carbonyl compounds for polymerizations with non-activated aromatic hydrocarbons

Reaction of carbonyl compounds bearing electron-withdrawing substituents with non-activated aromatic hydrocarbons proceeds selectively in trifluoromethanesulfonic acid (TFSA) at room temperature to give linear, high-molecular-weight polymers.

Synthesis and characterization of well-defined fully conjugated hyperbranched oligomers of β, β-dibromo-4-ethynylstyrene

Abstract Well-defined dendritic oligomers of poly(β,β-dibromo-4-ethynylstyrene) of the first and second generation havebeen synthesized by a stepwise synthesis, and characterized. It was found from n.m.r. analysis and by theoretical calculations that free rotation around formal single bonds is hampered by conjugation. All oligomers were found to be blue emitters with their emission maxima correlating with the number of repeating units. All dendrimers except dendrimer 12 (β,β-bis[β′,β′-di(β″,β″-dibromostyryl-4″-ethynyl)styryl-4′-ethynyl]-4-ethynylstyrene) showed two maxima in the excitation spectra.

Rectifying behavior of charge transfer complexes of tetrakis(dimethylamino)ethene with acceptor molecules: a theoretical study

The effect of electric field induced electron transfer on the rectification properties of molecular rectifiers based on charge transfer complexes of tetrakis(dimethylamino)ethane (TDAE) with acceptor molecules was explored. The current–voltage curves and the rectification ratios (RR) for two different molecular rectifiers were obtained using a direct ab initio method at M06/LACVP(d) level of theory in the range from −2 to +2 V. The highest RR of 25.7 was determined for the complex of TDAE with 2-nitropyrene-4,5,9,10-tetraone at 0.5 V (D1), while another rectifier [complex of TDAE with 2,7-dimethyl nitropyrene-4,5,9,10-tetraone (D2)] showed a maximum RR of only 2.9 at 0.3 V. The electric field induced electron transfer occurring in D1 creates a one-way conducting channel consisting of two SOMOs involving the entire D1 complex. In the case of D2, no electron transfer occurs at the applied bias voltages due to the relatively high energy difference between HOMO and LUMO.

Charge transfer complexes of fullerene[60] with porphyrins as molecular rectifiers. A theoretical study

Molecular diodes based on charge transfer complexes of fullerene[60] with different metalloporphyrins have been modeled. Their current–voltage characteristics and the rectification ratios (RR) were calculated using direct ab initio method at PBE/def2-SVP level of theory with D3 dispersion correction, for voltages ranging from −2 to +2 V. The highest RR of 32.5 was determined for the complex of fullerene[60] with zinc tetraphenylporphyrin at 0.8 V. Other molecular diodes possessed lower RR, however, all complexes showed RR higher than 1 at all bias voltages. The asymmetric evolutions and alignment of the molecular orbitals with the applied bias were found to be essential for generating the molecular diode rectification behavior. Metal nature of metalloporphyrins and the interaction porphyrin–electrode significantly affect RR of molecular diode. Large metal ions like Cd2+ and Ag2+ in metalloporphyrins disfavor rectification creating conducting channels in two directions, while smaller ions Zn2+ and Cu2+ favor rectification increasing the interaction between gold electrode and porphyrin macrocycle.