Ilya E. Nifant’ev

NEUTRAL AND CATIONIC 1,4-DIPHOSPHA-2-RHODA-3-THIA-4-FERROCENOPHANE

Abstract A mixed bidentate ferrocenyl ligand Fe(η5-C5Me4P(S)Ph2)(η5-C5Me4PPh2) (abbreviated {P,PS}) was synthesised and used for complexation with [RhCl(CO)2]2. The neutral [4]-ferrocenophane {P,PS}Rh(CO)Cl 2 and the unusual dimeric cationic species [{P,PS}Rh(CO)(μ-Cl)(CO)Rh{P,PS}]+ 3 were obtained and characterized by crystal structure analysis. During investigations on the catalytic properties of 2 in carbonylation, some aspects of its behavior towards iodomethane were elucidated.

Novel Cysteine Tags for the Sequencing of Non-Tryptic Disulfide Peptides of Anurans : ESI-MS Study of Fragmentation Efficiency

Mass spectrometry faces considerable difficulties in de novo sequencing of long non-tryptic peptides with S–S bonds. Long disulfide-containing peptides brevinins 1E and 2Ec from frog Rana ridibunda were reduced and alkylated with nine novel and three known derivatizing agents. Eight of the novel reagents are maleimide derivatives. Modified samples were subjected to MS/MS studies on FT-ICR and Orbitrap mass spectrometers using CAD/HCD or ECD/ETD techniques. Procedures, fragmentation patterns, and sequence coverage for two peptides modified with 12 tags are described. ECD/ETD and CAD fragmentation revealed complementary sequence information. Higher-energy collisionally activated dissociation (HCD) sufficiently enhanced y-ions formation for brevinin 1E, but not for brevinin 2Ec. Some novel tags [N-benzylmaleimide, N-(2,6-dimethylphenyl)maleimide] along with known N-phenylmaleimide and iodoacetic acid showed high total sequence coverage taking into account combined ETD and HCD fragmentation. Moreover, modification of long (34 residues) brevinin 2Ec with N-benzylmaleimide or N-(2,6-dimethylphenyl)maleimide yielded high sequence coverage and full C-terminal sequence determination with ECD alone.

Non-traditional Ziegler-Natta catalysis in a-olefin transformations: reaction mechanisms and product design

Abstract This paper describes our recent results in the field of zirconocene-catalyzed α-oltfin transformations, and focuses on questions regarding the reaction mechanism, rational design of zirconocene pre-catalysts, as well as prospective uses of α-olefin products. It has been determined that a wide range of α-olefin-based products, namely vinylidene dimers, oligomers and polymers, can be prepared via catalysis by zirconocene dichlorides, activated by a minimal (10–20 eq.) amount of MAO. We assumed that in the presence of minimal quantities of MAO, various types of zirconocene catalysts form different types of catalytic particles. In the case of bis-cyclopentadienyl complexes, the reactive center is formed under the influence of R2AlCl, which makes the chain termination via β-hydride elimination significantly easier, with α-olefin dimers being formed as the primary product. Bis-indenyl complexes and their heteroanalogues, form stable cationic catalytic particles and effectively catalyze the polymerization. Mono-indenyl and mono-substituted bis-cyclopentadienyl-ansa complexes catalyze α-olefin oligomerization. Effective catalysts of dimerization, oligomerization and polymerization of α-olefins in the presence of minimal MAO quantities are proposed. Prospects of using α-olefin dimers, oligomers and polymers in the synthesis of branched hydrocarbon functional derivatives (dimers), high quality, low viscosity motor oils (oligomers), and thickeners and absorbents (polymers) are examined.

A DFT Study of Ethylene Polymerization by Zirconocene-boron Catalytic Systems

The effect of anion A on the energy profile of the interaction Cp2ZrEt+A + C2H4 → Cp2ZrBu+A (A = CH3B(C6F5)3, B(C6F5)4) was studied. The addition of olefin to the ion pair Cp2ZrEt+A is characterized by an appreciable energy barrier and even can be the rate-determining stage of the overall process. The “front-perpendicular” approach of ethylene molecule to nonagostic isomer of Cp2ZrEt+A (5c) was found to be energetically most favorable. The results suggest that “nonagostic” reaction channels characterized by stabilization of intermediates and transition states should be growing in importance with enhancement of the nucleophilicity of the counterion.