Ti Group Metallocene-Catalyzed Synthesis of 1-Hexene Dimers and Tetramers

1-Hexene transformations in the catalytic systems L2MCl2–XAlBui2 (L = Cp, M = Ti, Zr, Hf; L = Ind, rac-H4C2[THInd]2, M = Zr; X = H, Bu i) and [Cp2ZrH2]2-ClAlR2 activated by MMAO-12, B(C6F5)3, or (Ph3C)[B(C6F5)4] in chlorinated solvents (CH2Cl2, CHCl3, o-Cl2C6H4, ClCH2CH2Cl) were studied. The systems [Cp2ZrH2]2-MMAO-12, [Cp2ZrH2]2-ClAlBui2-MMAO-12, or Cp2ZrCl2-HAlBui2-MMAO-12 (B(C6F5)3) in CH2Cl2 showed the highest activity and selectivity towards the formation of vinylidene head-to-tail alkene dimers. The use of chloroform as a solvent provides further in situ dimer dimerization to give a tetramer yield of up to 89%. A study of the reaction of [Cp2ZrH2]2 or Cp2ZrCl2 with organoaluminum compounds and MMAO-12 by NMR spectroscopy confirmed the formation of Zr,Zr-hydride clusters as key intermediates of the alkene dimerization. The probable structure of the Zr,Zr-hydride clusters and ways of their generation in the catalytic systems were analyzed using a quantum chemical approach (DFT).

CATALYTIC CONVERSION OF ETHYLENE ON SYSTEMS BASED ON THRICHLOROTRIS-(TETRAHYDROFURANATE)CHROMIUM(III) WITH SOS-TYPE LIGANDS IN COMBINATION WITH VARIOUS ORGANOALUMINUM COCATALYSTS

This work presents the results of studying the behavior of catalytic systems formed on the basis of trichlorotris-(tetrahydrofuranate)chromium(III) in the presence of sulfur-containing tridentate SOS-type ligands and activated by various organoaluminum compounds. In the formation of catalytic systems, the following compounds were used: SOS-type ligands - bis-(2-methylthioethyl) ether, bis-(2-ethylthioethyl) ether and bis-(2-phenylthioethyl) ether, organoaluminum compounds - triethylaluminum, triisobutylaluminum, tributylaluminum and methylaluminoxane. In the course of test experiments aimed at choosing an activator at a temperature of 40 °C and an ethylene pressure of 2 MPa, the best results were obtained for triethylaluminum. Therefore, further experiments on the catalytic conversion of ethylene were carried out only with this activator. To study the effect of the reaction temperature and ethylene pressure in the reaction zone, catalytic systems of the trichlorotris-(tetrahydrofuranate)chromium(III)/ligand/triethylaluminum composition were studied in the temperature range from 40 to 80 °C and an ethylene pressure of 2 - 3 MPa with a molar ratio of components Cr : L : AlEt3 = 1 : 1 : 20. As a result of studies, it was shown that in all cases when using tridentate ligands of the SOS type, the catalytic systems formed by us showed a tendency not only to polymerization, but also to oligomerization of ethylene. The best results in the field of ethylene oligomerization into hexenes were shown by the system of the composition trichlorotris-(tetrahydrofuranate)chromium(III) / bis-(2-methylthioethyl) ether/triethylaluminum, in which the content of the hexene fraction is 54 - 55 wt.%, while the selectivity to hexene-1 reaches 88 - 89%.

Catalytic Systems Based on Cp2ZrX2 (X = Cl, H), Organoaluminum Compounds and Perfluorophenylboranes: Role of Zr,Zr- and Zr,Al-Hydride Intermediates in Alkene Dimerization and Oligomerization

The activity and chemoselectivity of the Cp2ZrCl2-XAlBui2 (X = H, Bui) and [Cp2ZrH2]2-ClAlEt2 catalytic systems activated by (Ph3C)[B(C6F5)4] or B(C6F5)3 were studied in reactions with 1-hexene. The activation of the systems by B(C6F5)3 resulted in the selective formation of head-to-tail alkene dimers in up to 93% yields. NMR studies of the reactions of Zr complexes with organoaluminum compounds (OACs) and boron activators showed the formation of Zr,Zr- and Zr,Al-hydride intermediates, for which diffusion coefficients, hydrodynamic radii, and volumes were estimated using the diffusion ordered spectroscopy DOSY. Bis-zirconium hydride clusters of type x[Cp2ZrH2∙Cp2ZrHCl∙ClAlR2]∙yRnAl(C6F5)3−n were found to be the key intermediates of alkene dimerization, whereas cationic Zr,Al-hydrides led to the formation of oligomers.

Low-temperature reduction of acyclic carvomentholactone derivatives with diisobutylaluminum hydride in methylene chloride

Earlier, we discovered a novel reaction in the chemistry of organoaluminum compounds - the formation of O-isobutyl acetals during low-temperature (-70 °С) treatment of a number of seven-membered lactones with a twofold (or more) molar amount of diisobutylaluminium hydride in methylene chloride. In addition, it was shown that the acyclic derivatives of (-)-mentholactone - methyl 6-hydroxy-3,7-dimethyl-octanoate and its 6-oxo analogue - also enter into the low-temperature reduction reaction of diisobutylaluminum hydride in methylene chloride. Moreover, methyl 6-hydroxy-3,7-dimethyloctanoate in this reaction behaves similarly to (-)-mentholactone: when 4 equivalents of diisobutylaluminium hydride acts on it, the reaction proceeds with the predominant formation of isobutyl acetal as the only (2S,7S)-epimer. Methyl 6-oxo-3,7-dimethyl octanoate in a low-temperature reduction reaction with 4 equivalents of diisobutylaluminium hydride in methylene chloride acts as a mixture of (-)-mentholactone and isomentolactone, leading to a mixture of (2S,7S)-, (2S,7R)- and (2R,7R)-isobutyl acetals in a ratio of 3.2: 1.3: 1.0, respectively. In the present work, when low-temperature reduction was involved in the reaction with diisobutylaluminium hydride, methyl (3R)-6-hydroxy- or (3R)-6-oxo-3-isopropylheptanoates available from carvomentolactone reacted without the formation of isobutyl acetal: a mixture of (2: 1) 6-hydroxy-(3R)-isopropylheptanal and (4R)-isopropyl-7-methyloxepan-2-ol was obtained.

Reaction of Dialumane Incorporating Bulky Eind Groups with Pyridines

The reaction of the bulky Eind-based dialumane, (Eind)HAl(μ-H)2AlH(Eind) (1) (Eind = 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl), with pyridines is described. When 1 was treated with pyridine (Py) in toluene, the Py adduct of aryldihydroalumane, Py→AlH2(Eind) (2), was initially formed. Then, the hydroalumination of Py took place to yield the Py-bound aryl(1,4-dihydropyrid-1-yl)hydroalumane, Py→AlH(1,4-dihydropyrid-1-yl)(Eind) (3). A similar reaction with a stronger Lewis base, 4-pyrrolidinopyridine (PPy), produced the stable PPy adduct, PPy→AlH2(Eind) (4). The resulting organoaluminum compounds have been fully characterized by NMR spectroscopy as well as X-ray crystallography. The reaction mechanism from 1 to 3 via 2 has been examined by deuterium labeling experiments using (Eind)DAl(μ-D)2AlD(Eind) (1-d4).