Well-defined phosphate yttrium dialkyl complexes for catalytic stereo-controllable 1,4-polymerization of isoprene

Oxygen ligation is envisioned to provide a stable and distinctive coordination environment to the strongly oxophilic rare-earth metals. However, the well-defined dialkyl complexes bearing oxyanion ancillary ligand had been rarely addressed for the instability of the complexes and the shortage of easily available ligands. Herein, we report the synthesis of phosphate ligated dialkyl yttrium complexes（PYR2） featuring a high stability and a tunable ligand. Treated with the borate reagent, the phosph...     

Solvent-free telomerization of isoprene with alcohols catalyzed by palladium(ɪɪ) carbene complexes

Russian Chemical Bulletin - The effect of various factors on the activity and selectivity of palladium N-heterocyclic carbene (NHC) complexes in the telomerization of isoprene with alcohols has...     

Short-time isoprene polymerization under the action of a titanium–magnesium catalyst

The short-time polymerization of isoprene under the action of a TiCl₄/MgCl2?i-Bu₃Al heterogeneous catalyst has been investigated. Pulse mixing of the catalyst and monomer in a cylindrical tubular reactor with a certain length followed by ethanol injection has made it possible to carry out polymerization for 0.1?0.7 s. In the first 0.3 s, when there is a considerable rise in the activity of the catalyst, living polymerization of isoprene takes place. In this period, polyisoprene has up to 95% trans-1,4 units. Extending the polymerization time to 0.7 s diminishes the average molar mass of polyisoprene, broadens its molar mass distribution, and decreases the concentration of trans-1,4 units to 83%. The data of this study have been analyzed on the basis of the kinetic continuity of the polymer chain initiation and growth.     

Determination of configurational–isomeric composition of synthetic isoprene rubbers using NMR spectroscopy

Production pieces of synthetic isoprene rubbers are studied using the nuclear magnetic resonance spectroscopy method. The measurements are performed by ¹Н and ¹³С NMR spectroscopy with variation of the conditions of sample preparation and taking and processing of spectra, which allows improving the accuracy of quantitative analysis of the content of monomer units characterized by different configurations.     

The addition of diborane to isoprene and the synthesis of β-methyltetramethylene diboric acid

Summary By adding diborane to isoprene we have obtained bis-1,4-(1-bora-2-methylcyclopentyl)-2-methylbutane, from which, by the action of boron trichloride and then water, we have synthesized -methyltetramethylene diboric acid.     

Kinetic features of short-time polymerization of isoprene in the presence of supported titanium–magnesium catalyst

Short-time polymerization of isoprene under the action of supported titanium–magnesium catalyst is carried out. The pulsation mixing of the reagent flows and the unit design features allow one to reduce the average residence time of reagents in the reaction zone and to study the first 0.7 s of the isoprene polymerization. It is found that, very early in polymerization, the propagation of polyisoprene macromolecules proceeds on the surface of the primary aggregates of catalyst particles characteristic of a high trans-1,4 specificity via the “living” mechanism with a high rate. Furthermore, the fragmentation of the initial aggregates of the catalyst particles occurs, which results in formation of new polymerization centers, a decrease in the average molecular masses of polyisoprene, and a broadening of the polymer MMD. The results are explained by the existence of a range of the kinetic continuity of the rapid initiation stage and several subsequent stages of macromolecule propagation, followed by a significant decrease in the chain propagation rate constant compared to the initiation constant.     

De-protonation of (η4-isoprene)Fe(CO)3; an isoprene anion equivalent

(η⁴-Isoprene)Fe(CO)₃ can be deprotonated with lithium diisopropylamide. The resulting coordinated isoprene anion reacts with electrophiles at low temperature, but rearranges to an isomeric (η⁴-trimethylenemethane)Fe(CO)₃ anion derivative at higher temperatures.     

Thermal Decomposition of Polyisoprene,Poly(p-isopropyl α-Methylstyrene), and Poly(isoprene/p-isopropyl α-Methylstyrene)

Thermal decompositions of polyisoprene, poly(p-isopropyl α-methylstyrene) (PPIPαMS), and poly(isoprene/p-isopropyl α-methylstyrene) (sample M-32) were carried out at various temperatures in the range 200–340° C in a differential thermo-gravimetric apparatus. The undecomposed polymers as well as their decomposed residues were analyzed by gel-permeation chromatography (GPC), infrared spectroscopy (IR), and nuclear magnetic resonance (NMR). Based on the changes observed in the distribution of molecular weights, depolymerization is the predominant step in the decomposition of PPIPAMS and polymer M-32, whereas random scissions predominate in the case of polyisoprene. The combined data of GPC, IR, and NMR indicate that only interchain reactions leading to the formation of cyclized products are present in the decomposition of polyisoprene while interchain as well as intrachain reactions are operative in the case of polymer M-32.     

Vapor-phase synthesis of isoprene from formaldehyde and isobutylene over CuSO4?MOx/SiO2 catalysts

Vapor-phase synthesis of isoprene from formaldehyde and isobutylene over CuSO₄–MO_x/SiO₂ catalysts has been studied. The results show that CuSO₄–MO_x/SiO₂ catalysts exhibit a good catalytic activity; especially when the metal oxides have appropriate basicity, is isoprene yield greatly enhanced. The results of product analysis indicate that there are side-reactions during isoprene production, which are isoprene hydrogenation, polymerization of isobutylene, copolymerization of isobutylene and isoprene, and reaction of C₅ aldehyde and ketone formed during isoprene production. In addition, catalytic behavior of the catalysts and probable mechanism of side-reactions are discussed.

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CuSO₄–MO_x/SiO₂. ; , . , , , , , , C₅ , . .

     

Derivatives of dolichyl phosphate with fluorescent label. Analogs of dolichyl phosphate with different lengths of isoprene chain,containing the (1-naphthyl)amino group in the ω-fragment

A series of fluorescent dolichyl phosphates containing the (1-naphthyl)amino group in the -fragment of the chain and possessing a definite distance between fluorophoric and phosphate groups were synthesized for studying the interactions of dolichyl phosphates with enzymes and biological membranes. The corresponding terminal 2,3-dihydrohexadeca-, 2,3-dihydroundeca-, and 2,3-dihydrooctaprenol epoxides were obtained from racemic dolichols (prepared from natural polyprenol mixtures) by van Tamelen epoxidation of their -isoprene unit and separated by preparative HPLC. These epoxides were converted to aldehydes, which were subjected to reductive amination with 1-aminonaphthalene and NaBH₄ with subsequent phosphorylation of the resulting amino alcohols.     

Hydrocarboxylation of isoprene catalyzed by iodo-carbonylrhodium derivatives. Spectroscopic evidence for participation of H+ ··· Rh(CO)2I2− tight ion pairs and cis-Rh(CO)2(H2O)I in catalysis

Hydrocarboxylation of isoprene catalyzed by iodocarbonylrhodium derivatives is described. Either 4-methyl-3-pentenoic (pyroterebic) acid or its lactone derivative (γ,γ-dimethyl-γ-butyrolactone) can be selectively produced in high yield depending on the experimental conditions. Spectroscopic evidence indicates the possible participation of H⁺ ··· Rh(CO)₂I₂⁻ tight ion pairs and/or cis-Rh(CO)₂(H₂O)I in the catalysis. The identification of these two new species is based on spectroscopic investigation of the interconversion reactions between solvent-separated [H₃O]⁺[Rh(CO)₂X₂]⁻ ions and [Rh(CO)₂X]₂ (X = Cl, I).     

Facile synthesis of (±)-2,6-dimethyloctan-1-ol formate,the biologically active analog of the smaller flour beetle aggregation pheromone,from 1-allyloxy- and 1-benzyloxy-2,6-dimethyl-2,7-octadienes,the telomers of isoprene with allyl and benzyl alcohols

A careful investigation of the telomerization of isoprene with allyl, benzyl, 2-chloroethyl and methyl alcohols on -allylpalladium complex catalysts was carried out. The structures of the obtained telomers were determined by¹H NMR spectroscopy. 1-Alkoxy-2,6-dimethyl-2,7-octadiene is a predominant telomer. 2,6-Dimethyloctan-1-ol, which reacts with HCOOH to give (±)-2,6-dimethyloctan-1-ol formate in high yield, was obtained from 1-allyloxy- and 1-benzyloxy-2,6-dimethyl-2,7-octadienes by the removal of allyl and benzyl protective groups and by the hydrogenation of double bonds.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1539–1543, August, 1995.