Electrochemistry of bis(indenyl)dimethylzirconium complex—the precursor of the olefin polymerization catalyst

The reduction in THF and oxidation in CH₂Cl₂ of the bent-sandwich complex (η⁵-lnd)₂ZrMe₂ (1) (Ind=C₉H₇, indenyl) were studied by cyclic voltammetry. Complex1 in THF undergoes one-electron reduction to radical anion1 ⁻, which partially decomposes with the liberation of the Ind⁻ anion. Even at −45°C the one-electron oxidation leads to the formation of an unstable 15-electron radical cation undergoing fast heterolytic decomposition to the Me^• radical and (η⁵-lnd)₂ZrMe² cation, which is the key reaction center in the catalytic polymerization of olefins. Comparative analysis of electron-transfer-induced transformations of bent-sandwich dimethyl and dichloride zirconocenes of the general formula L₂ZrX₂ (L=η⁵-lnd, η⁵-Cp: X=Xl, Me) was performed. The material of the paper was first reported at the 195th Meeting of the Electrochemical Society (see Ref. 1). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 59–62, January, 2000.     

Acidity effects of Hβ zeolite on olefin alkylation of thiophenic sulfur in gasoline

Olefin alkylation of thiophenic sulfur process was carried out in model gasoline, using Hβ zeolites with different Si/Al2 ratios as catalysts. In particular, the influence of acid properties of Hβ zeolites on its catalytic ability for the thiophene alkylation, xylene alkylation and hexene oligomerization was investigated. The results showed that the acidity of the Hβ zeolite was increased with the decrease of Si/Al2 ratio, but its catalytic ability was not always increased. In fact, it reached the maximal catalytic ability at Si/Al2 ratio of 66, and under the reaction conditions of 60 ℃, 1.5 MPa, WHSV 3.0 h-1and time on stream 2 h. At the ratio, the conversion of thiophene, xylene, and oligomerized hexene were 96.6%, 2.7% and 2.8%, respectively. An optimal Si/Al2 ratio exists for the catalytic performance of H/3 zeolite. By investigating the coke deposition of the used H/3 zeolite catalysts, it has been found that the optimal Si/Al2 ratio is attributed to the combined effect of the carbocation activation capability and the hydrogen transformation capability of the H/3 zeolite catalyst.     

Acidity effects of Hβ zeolite on olefin alkylation of thiophenic sulfur in gasoline

Olefin alkylation of thiophenic sulfur process was carried out in model gasoline, using Hβ zeolites with different Si/Al2 ratios as catalysts. In particular, the influence of acid properties of Hβ zeolites on its catalytic ability for the thiophene alkylation, xylene alkylation and hexene oligomerization was investigated. The results showed that the acidity of the Hβ zeolite was increased with the decrease of Si/Al2 ratio, but its catalytic ability was not always increased. In fact, it reached the maximal catalytic ability at Si/Al2 ratio of 66, and under the reaction conditions of 60 ℃, 1.5 MPa, WHSV 3.0 h^-1 and time on stream 2 h. At the ratio, the conversion of thiophene, xylene, and oligomerized hexene were 96.6%, 2.7% and 2.8%, respectively. An optimal Si/Al2 ratio exists for the catalytic performance of Hβ zeolite. By investigating the coke deposition of the used Hβ zeolite catalysts, it has been found that the optimal Si/Al2 ratio is attributed to the combined effect of the carbocation activation capability and the hydrogen transformation capability of the Hβ zeolite catalyst.     

What is the initiation step of the Grubbs-Hoveyda olefin metathesis catalyst?

Density function theory calculations reveal that the Grubbs-Hoveyda olefin metathesis pre-catalyst is activated by the formation of a complex in which the incoming alkene substrate and outgoing alkoxy ligand are both clearly associated with the ruthenium centre. The computed energies for reaction are in good agreement with the experimental values, reported here.     

Atropselective alkylation of biaryl compounds by means of transition metal-catalyzed C–H/olefin coupling

The reaction of 2-(1-naphthyl)-3-methylpyridine with olefins in the presence of [RhCl(coe)₂]₂ and PCy₃ as the catalyst resulted in the alkylation of the naphthyl ring at the 2-position in good yield. The replacement of PCy₃ with the chiral ferrocenyl phosphine, (R),(S)-PPFOMe, as the ligand resulted in atropselective alkylation of the naphthylpyridine derivatives. Ethylene reacted with the biaryl compounds to give the corresponding addition products in moderate yields with fair to good ee's (up to 49% ee).     

Electronic control of the competitive π donation in heteroatom substituted CpFe(CO)2(olefin)BF4 complexes and the resulting influence on the symmetry of the metal to olefin bond

Nucleophilic, single substitution of with para substituted anilines was used to prepare a series of cis Fp olefin complexes 10-14 of the general formula, , where X = OMe (10), Me (11), Cl, (12), COMe (13), and CN (14). These complexes contain both vinyl oxygen and vinyl nitrogen π donors capable of p-π donation to the olefin. This series allows a comparison of competitive π donor strengths as X is varied across the series. Correlation of the Hammett σ_para parameters for X with the ¹³C NMR shifts of the metal coordinated vinyl carbons demonstrated that as the electron withdrawing character of the para substituent was increased, the aniline (while still the dominant π donor) competed less effectively with the cis ethoxy group, moving the Fp⁺ moiety toward a more central point along the olefin face. The implication of such control for the nucleophilic substitution chemistry of these complexes is discussed.     

Photopromoted methoxycarbonylation of olefin with methyl formate by Co（OAc）2

The photopromoted methoxycarbonylation of olefin with methyl formate catalyzed by Co(OAc)2 at ambient conditions has been carried out.The results indicated that the reaction activity increased with the increasing temperature.Methyl formate decomposed into CO and CH_3OH firstly under irradiation,and then the methoxycarbonylation of olefin proceeded under catalysis of Co(OAc)_2. The mechanism of methyl formate participating in the methoxycarbonylation is verified by the IR analysis and the labeling experiments of CD_3OD and CH_3~(18)OH.     

The nature of the catalytically active species in olefin dioxygenation with PhI(OAc)2: metal or proton?

Evidence for the protiocatalytic nature of the diacetoxylation of alkenes using PhI(OAc)(2) as oxidant is presented. Systematic studies into the catalytic activity in the presence of proton-trapping and metal-complexing agents indicate that protons act as catalysts in the reaction. Using triflic acid as catalyst, the selectivity and reaction rate of the conversion is similar or superior to most efficient metal-based catalysts. Metal cations, such as Pd(II) and Cu(II), may interact with the oxidant in the initiation phase of the catalytic transformation; however, 1 equiv of strong acid is produced in the first cycle which then functions as the active catalyst. Based on a kinetic study as well as in situ mass spectrometry, a mechanistic cycle for the proton-catalyzed reaction, which is consistent with all experimental data presented in this work, is proposed.     

An α-Diimine-Nickel(II) catalyst bearing an electron-withdrawing substituent for olefin polymerization

A Br-substituted α-diimine ligand, bis[N,N′-(4-bromo-2,6-dimethylphenyl)imino]-2,3-butadiene L1, and its corresponding Ni(II) complex, {bis[N,N′-(4-bromo-2,6-dimethylphenyl)imino]-2,3-butadiene} dibromonicke [NiBr ₂ (L1)], have been synthesized and characterized. The crystal structure of the free ligand (L1) was determined by X-ray crystallography. Two α-diimine-Ni(II) catalysts, {bis[N,N′-(2,4,6-dimethylphenyl)imino]-2,3-butanedione} dibromonickel [NiBr ₂ (L2)] and {bis[N,N′-(2,6-dimethylphenyl)imino]-2,3-butanedione} dibromonickel [NiBr ₂ (L3)], were also synthesized and characterized for comparison. The complex [NiBr ₂ (L1)], when activated by diethylaluminum chloride, produces the most active catalytic system for the polymerization of ethylene among the three complexes. NMR analysis shows that the degree of branching of polyethylene increases in the presence of electron-withdrawing groups under the same reaction conditions.     

Mono-η-arenebis(trimethylphosphine(rhenium chemistry: alkyl,hydrido, halogeno and olefin derivatives

Co-condensation of rhenium atoms with a benzene-trimethylphosphine mixture gives the dimer [Re(ν-C₆H₆)(PMe₃)₂]₂ which is a precursor to the new compounds Re(η-C₆H₆)(PMe₃)₂R (R = H, Cl, I, Me, Et, CHCH₂ or Ph), [Re(η-C₆H₆)(PMe₃)₂X₂]BF₄ (X₂ = H₂ or HI), [Re(η-C₆H₆)(PMe₃)₂H₂][BF₄]₂, and [Re(η-C₆H₆)(PMe₃)₂L]BF₄ (L = η-C₂H₄ or CO). Co-condensation of manganese atoms with benzene-trimethylphosphine gives Mn(η-C₆H₆)(PMe₃)₂H.     

Influence of quaternary onium salts,crown ethers and cryptands on olefin epoxidations promoted by HOCl/ClO− in the Presence of Mn(III)-tetrakis(2,6-dichlorophenyl)porphyrin chloride

Reaction rates of alkene epoxidations, promoted by aqueous NaOCl and catalyzed by Mn(III)-tetrakis(2,6-dichlorophenyl)porphyrin chloride1 (P) in the presence of a lipophilic axial ligand (L) (e.g.N-hexylimidazole) and carried out under H₂O/CH₂Cl₂ two phase conditions at 0°C, are strongly enhanced by lowering the pH of the aqueous phase from 12.7 to 9.5. Under these conditions, a further relevant increase in the reaction rates can be achieved by adding phase-transfer catalysts (PT), e.g. quaternary ammonium salt 3, lipophilic crown ether4 or cryptand5, provided that the amount of L is very small (L/P=1 for very reactive alkenes, e.g. cyclooctene, and 10 for poorly reactive ones, e.g. 1-dodecene). In the case of cyclooctene epoxidation, the use of 0.006–0.03 mol. equiv. of PT completes the reaction in 1–10 min., the initial rates being up to 600 turnovers/min. with (2.2.2,C₁₀) cryptand. In the absence of the axial ligand, the quaternary ammonium salt3 and cryptand5 show an inhibitory effect. Such an effect is due to the formation of the poorly reactive Mn(P)CI species, by Cl– extraction to the organic phase. However, dibenzo crown ether 4 does not show this effect. In the presence of 4, and with L/P =1, the 1-dodecene epoxidation reaches 94% in 1 min. The unique behavior of crown ethers can be explained by their ineffectiveness in extracting alkali chlorides, providing a very low concentration of Cl– in the organic phase and thus avoiding the Mn(III)-porphyrin deactivation.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

A highly regioselective hydroformylation of an α-chiral olefin to produce a versatile trifunctionalised orthogonally protected C5 synthon

This paper describes a highly regioselective hydroformylation of (R)-N-phthalimido-vinylglycinol, [(R)-PVG]. By judicious choice of the reaction conditions, catalyst-controlled preferential formation of the linear regioisomer could be achieved in excellent yield. The hydroformylation product cyclised to a hemi-acetal, which is an orthogonally protected trifunctionalised enantio-enriched C5 synthon. The value of this versatile intermediate was demonstrated by the ready formation of enantio-enriched amino-diols, diamino-alcohols and differentially protected (R)-3-aminopiperidine.     

Polar comonomer incorporation using cationic Ni α-diimine olefin polymerization catalysts

<正>Polyolefins are an indispensable class of materials that have become the most widely produced and utilized polymers today. They are readily synthesized from cheap and abundant monomer feedstocks, such as ethylene and propylene, and are capable of achieving a vast array of thermal and mechanical properties based upon their composition and to-     

Complexes of titanium(IV) chloride with N-(3,5-R,R′-salicylidene)-2(3,4)-[bis(5-methyl-2-furyl)methyl]aniline, a novel type of phenoxyimine catalysts for olefin polymerization

New representatives of chelate-type titanium(IV) salicylideneaniline complexes with bis(5-methyl-2-furyl)methyl substituents in the aniline fragment are synthesized. In the presence of poly(methylalumoxane), these complexes catalyze ethylene and propylene polymerization. The effect of the position of substituents in the ligands on the activities of the catalysts is studied. High-molecular-weight linear polyethylene (M _w ≈ 172200–300000, M _w/M _n ≈ 2–3) and high-molecular-weight atactic elastic polypropylene (M _w ≈ 1000000, M _w/M _n ≥ 7.0) are obtained. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1730–1737, October, 2006.     

Iridium pentahydride complex catalyzed formation of CC bond by CH bond activation followed by olefin insertion

The formation of carbon-carbon bond was found to occur by first carbon-hydrogen bond activation followed by olefin insertion under the catalysis of an iridium pentahydride complex.     

Fourier-transform i.r. gas chromatography—mass spectrometry study of varying light olefin reactivity on dealuminated ZSM-5

Olefin oligomerization and alkylation (by methanol) of ethene, propene, and isobutene on HZSM-5 have been studied in typical conditions of the catalytic Mobil methanol to gasoline (MTG) process. This has been to identify the most likely light olefin involved as a key intermediate and the most likely mechanism by which such a light olefin propagates to gasoline in the MTG process. Reactions involving bulky intermediates are restricted within the narrow channels of ZSM-5. The oligomerization of ethene and isobutene appears to be an example of such restricted reactions. Zeolite dealumination seems to assist in overcoming the steric barrier by increasing both the zeolite pore volume and the population of the site (silanol) hosting the adsorbate. Spectral i.r. evidence reveals a role of zeolite Lewis acidity as a precursor in initiating olefin protonation by the zeolite Brønsted acidity. Both i.r. and GC—MS data consistently reveal a product distribution similar to that obtained in the MTG process, which suggests a dominant oligomerization and/or alkylation to be the mechanism leading to gasoline in the MTG process. However, the higher reactivity detected for olefin alkylation indicates alkylation to be the favoured mechanism. Propene is more likely to be a key intermediate, whereas isobutene contributes with a role being increasingly dominant over the more dealuminated ZSM-5 surfaces. Ethene, in contrast, shows poor reactivity, which can be enhanced by the zeolite dealumination.     

MgCl(2)·4((CH(3))(2)CHCH(2)OH): A new molecular adduct for the preparation of TiCl(x)/MgCl(2) catalyst for olefin polymerization

A new molecular adduct of MgCl(2) with isobutanol, namely MgCl(2)·4((CH(3))(2)CHCH(2)OH) (MgiBOH), has been prepared as a precursor to the supporting material for an olefin polymerization catalyst. The MgiBOH adduct and final titanated Ziegler-Natta catalysts have been thoroughly characterized by powder XRD, thermal analysis, Raman spectroscopy and solid-state NMR for structural and spectroscopy aspects. A peak observed at 712 cm(-1) in the Raman spectra of MgiBOH indicates the characteristic Mg-O(6) breathing mode and the formation of the adduct. The diffraction feature at 2θ = 7.8° (d = 11.223 ?) in the XRD confirms the adduct formation and the layered structure. The aim of the present article is to study how the insertion of a bulky isobutanol moiety affects the structural and electronic properties of the MgCl(2)·isobutanol molecular adduct. Indeed, the focus of the present study is to explore how the presence of isobutanol, in the initial molecular adduct, influences the final Z-N catalyst properties and its activity.     

Substitution effects on olefin epoxidation catalyzed by Oxoiron(IV) porphyrin π-cation radical complexes: A dft study

The effects of peripheral fluorine atoms on epoxidation reactions of ethylene by oxoiron(IV) porphyrin cation radical complex in the quartet and sextet spin multiplicities are systematically investigated using the DFT method. The overall reaction routes are determined using a model system of ethylene and Fe(IV)OCl-porphyrin with substituted fluorine atoms. By obtaining the energy diagrams and electron- and spin-density difference contour maps of the transition states and intermediate compounds, we confirm that the electron-withdrawing by peripheral fluorine atoms enhances the reactivity as the number of fluorine atoms increases, as is observed experimentally. The intersystem crossing between the quartet and sextet spin multiplicities is discussed by means of the intrinsic reaction coordinate method. We conclude that the rate-determining step is located at the first transition state (TS1) for the activation of CC and FeO bonds, and the ground electronic state changes from quartet to sextet around the TS1. © 2019 Wiley Periodicals, Inc.