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Konstantin P Bryliakov Nina V Semikolenova Vladimir A Zakharov Martin Ystenes Evgenii P Talsi 《Journal of organometallic chemistry》2003,683(1):92-102
Using 1H- and 13C-NMR spectroscopies, cationic intermediates formed by activation of L2ZrCl2 with methylaluminoxane (MAO) in toluene were monitored at Al/Zr ratios from 50 to 1000 (L2 are various cyclopentadienyl (Cp), indenyl (Ind) and fluorenyl (Flu) ligands). The following catalysts were studied: (Cp-R)2ZrCl2 (R=Me, 1,2-Me2, 1,2,3-Me3, 1,2,4-Me3, Me4, Me5, n-Bu, t-Bu), rac-ethanediyl(Ind)2ZrCl2, rac-Me2Si(Ind)2ZrCl2, rac-Me2Si(1-Ind-2-Me)2ZrCl2, rac-ethanediyl(1-Ind-4,5,6,7-H4)2ZrCl2, (Ind-2-Me)2ZrCl2, Me2C(Cp)(Flu)ZrCl2, Me2C(Cp-3-Me)(Flu)ZrCl2 and Me2Si(Flu)2ZrCl2. Correlations between spectroscopic and ethene polymerization data for catalysts (Cp-R)2ZrCl2/MAO (R=H, Me, 1,2-Me2, 1,2,3-Me3, 1,2,4-Me3, Me4, Me5, n-Bu, t-Bu) and rac-Me2Si(Ind)2ZrCl2 were established. The catalysts (Cp-R)2ZrCl2/AlMe3/CPh3+B(C6F5)4− (R=Me, 1,2-Me2, 1,2,3-Me3, 1,2,4-Me3, Me4, n-Bu, t-Bu) were also studied for comparison of spectroscopic and polymerization data with MAO-based systems. Complexes of type (Cp-R)2ZrMe+←Me−-Al≡MAO (IV) with different [Me-MAO]− counteranions have been identified in the (Cp-R)2ZrCl2/MAO (R=n-Bu, t-Bu) systems at low Al/Zr ratios (50-200). At Al/Zr ratios of 500-1000, the complex [L2Zr(μ-Me)2AlMe2]+[Me-MAO]− (III) dominates in all MAO-based reaction systems studied. Ethene polymerization activity strongly depends on the Al/Zr ratio (Al/Zr=200-1000) for the systems (Cp-R)2ZrCl2/MAO (R=H, Me, n-Bu, t-Bu), while it is virtually constant in the same range of Al/Zr ratios for the catalytic systems (Cp-R)2ZrCl2/MAO (R=1,2-Me2, 1,2,3-Me3, 1,2,4-Me3, Me4) and rac-Me2Si(Ind)2ZrCl2/MAO. The data obtained are interpreted on assumption that complex III is the main precursor of the active centers of polymerization in MAO-based systems. 相似文献
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Konstantin P. Bryliakov 《Mendeleev Communications》2021,31(1):8-13
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Complexes [(BPMEN)Fe(II)(CH(3)CN)(2)](ClO(4))(2) (1, BPMEN = N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane) and [(TPA)Fe(II)(CH(3)CN)(2)](ClO(4))(2) (2, TPA = tris(2-pyridylmethyl)amine) are among the best nonheme iron-based catalysts for bioinspired oxidation of hydrocarbons. Using EPR and (1)H and (2)H NMR spectroscopy, the iron-oxygen intermediates formed in the catalyst systems 1,2/H(2)O(2); 1,2/H(2)O(2)/CH(3)COOH; 1,2/CH(3)CO(3)H; 1,2/m-CPBA; 1,2/PhIO; 1,2/(t)BuOOH; and 1,2/(t)BuOOH/CH(3)COOH have been studied (m-CPBA is m-chloroperbenzoic acid). The following intermediates have been observed: [(L)Fe(III)(OOR)(S)](2+), [(L)Fe(IV)═O(S)](2+) (L = BPMEN or TPA, R = H or (t)Bu, S = CH(3)CN or H(2)O), and the iron-oxygen species 1c (L = BPMEN) and 2c (L = TPA). It has been shown that 1c and 2c directly react with cyclohexene to yield cyclohexene oxide, whereas [(L)Fe(IV)═O(S)](2+) react with cyclohexene to yield mainly products of allylic oxidation. [(L)Fe(III)(OOR)(S)](2+) are inert in this reaction. The analysis of EPR and reactivity data shows that only those catalyst systems which display EPR spectra of 1c and 2c are able to selectively epoxidize cyclohexene, thus bearing strong evidence in favor of the key role of 1c and 2c in selective epoxidation. 1c and 2c were tentatively assigned to the oxoiron(V) intermediates. 相似文献
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Evgenii P. Talsi Anna A. Bryliakova Konstantin P. Bryliakov 《Chemical record (New York, N.Y.)》2016,16(2):924-939
Optically pure chiral epoxides and sulfoxides are ubiquitous building blocks in fine organic synthesis, employed in the pharmaceutical, agrochemical, and cosmetic industries. On the road to chiral epoxides and sulfoxides, efficient and stereoselective transition metal‐based catalysts are the most promising guides. Among transition metals, we favor titanium for its cheapness and availability, nontoxicity, and well‐known ability to catalyze a variety of stereoselective transformations, including oxidations with environmentally benign H2O2. In this personal account, we summarize the state‐of‐the‐art of rational design of chiral titanium(IV) salan and salalen catalysts, and investigations of their catalytic reactivities and stereoselectivities in the epoxidations of olefins and oxidations of thioethers, unraveling the peculiarities and mechanisms of their catalytic action. 相似文献
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<正>Introduction of polar comonomers into polyethylene is highly challenging, paving the way to tuning the copolymers’ mechanical properties, adhesion/compatibility, and biodegradability. Polar-group tolerant single-site palladium and, more tempting, nickel-based catalysts have demonstrated promising reactivities in the ethylene copolymerization with polar comonomers via coordination/insertion mechanism, providing tighter control of polymer micro- 相似文献
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Intermediates of chromium-salen catalyzed alkene epoxidations were studied in situ by EPR, (1)H and (2)H NMR, and UV-vis/NIR spectroscopy (where chromium-salens were (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamino chromium(III) chloride (1) and racemic N,N'-bis(3,4,5,6-tetra-deuterosalicylidene)-1,2-cyclohexanediamino chromium(III) chloride (2)). High-valence chromium complexes, intermediates of epoxidation reactions, were detected and characterized by EPR and NMR. They are the reactive mononuclear oxochromium(V) intermediate (A) Cr(V)O(salen)L (where L = Cl(-) or a solvent molecule) and an inactive chromium-salen binuclear complex (B) which acts as a reservoir of the active species. The latter complex demonstrates an EPR signal characteristic of oxochromium(V)-salen species and (1)H NMR spectra typical for chromium(III)-salen complexes, and it is identified as mixed-valence binuclear L(1)(salen)Cr(III)OCr(V)(salen)L(2) (L(1), L(2) = Cl(-) or solvent molecules). The intermediates Cr(V)O(salen)L and L(1)(salen)Cr(III)OCr(V)(salen)L(2) exist in equilibrium, and their ratio can be affected by addition of donor ligands (DMSO, DMF, H(2)O, pyridine). Addition of donor additives increases the fraction of A over that of B. The same two complexes can be obtained with m-CPBA as oxidant. Reactivities of the Cr(V)O(salen)L complexes toward E-beta-methylstyrene were measured in DMF. The L(1)(salen)Cr(III)OCr(V)(salen)L(2) intermediate has been proposed to be a reservoir of the true reactive chromium(V) species. The chromium-salen catalysts demonstrate low turnover numbers (ca. 5), probably due to ligand degradation processes. 相似文献
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K.P. Bryliakov I.V. Khavrutskii E.P. Talsi O.A. Kholdeeva 《Reaction Kinetics and Catalysis Letters》2000,71(1):183-191
Using EPR, high-valent MnIV complexes have been detected in Mukaiyama's catalytic system, MnIII(Salen)/Isobutyraldehyde/O2, and shown to form also in the model system MnIII(Salen)/Peroxyisobutyric acid. Their possible role in alkene epoxidation is discussed. 相似文献