Nina V. Semikolenova

Polymerization of ethylene catalyzed by iron complex bearing 2,6-bis(imine)pyridyl ligand : 1H and 2H NMR monitoring of ferrous species formed via catalyst activation with AlMe3, MAO, AlMe3/B(C6F5)3 and AlMe3/CPh3(C6F5)4

1 H and 2 H NMR spectroscopic monitoring of ferrous species formed via interaction of 2,6-bis[1-2,6-dimethylphenylimino)ethyl]pyridineiron (II) chloride (1) with AlMe 3 , MAO, AlMe 3 /B(C 6 F 5 ) 3 and AlMe 3 /CPh 3 (C 6 F 5 ) 4 is reported. At interaction of 1 with MAO in toluene solution, the new stable heterodinuclear neutral complexes with proposed structures LFe(II)(Cl)(u-Me) 2 AlMe 2 and LFe(II)(Me)(u-Me) 2 AlMe 2 are formed (L is initial tridentate ligand). Complex LFe(II)(Cl)(u-Me) 2 AlMe 2 predominates at low Al/Fe ratios (less than 50), while LFe(II)(Me)(U-Me) 2 AlMe 2 at high Al/Fe ratios (more than 500). Complex assigned to LFe(II)(Me)(u-Me) 2 AlMe 2 can be prepared via interaction of 1 with AlMe 3 . Activation of LFe(II)(Me)(u-Me) 2 AlMe 2 by B(C 6 F 5 ) 3 and CPh 3 B(C 6 F 5 ) 4 gives rise to formation of new complexes with proposed structures [LFe(u-Me) 2 AlMe 2 ] + [MeB(C 6 F 5 ) 3 ] - and [LFe(u-Me) 2 AlMe 2 ] + [B(C 6 F 5 ) 4 ] - . Unexpectedly, the activity at ethylene polymerization was even higher for 1/AlMe 3 than for 1/MAO catalytic system. The co-catalytic activity of MAO towards 1 dramatically decreased with the diminishing of AlMe 3 content in the composition of MAO. Activity of the catalyst 1/AlMe 3 and the molecular structure of polyethylene produced do not change noticeably at the addition of B(C 6 F 5 ) 3 to 1/AlMe 3 . These data allow to suggest, that active species of 1/AlMe 3 and 1/MAO systems are neutral methylated ferrous complexes but not cationic intermediates. Probably, complex LFe(II)(Me) 2 AlMe 2 is the closest precursor of these active species.

The metallocene/methylaluminoxane catalysts formation : EPR spin probe study of Lewis acidic sites of methylaluminoxane

Abstract Using stable nitroxyl radical 2,2,6,6-tetramethylpiperidine- N -oxyl (TEMPO) as a spin probe, Lewis acidic sites of methylaluminoxane (MAO) were identified. It was found that MAO contains two types of acidic sites. TEMPO, coordinated to the sites I and II, exhibits in the EPR spectra triplet ( g o =2.0047, a N =18.6 G) and triplet of sextets ( g o =2.0045, a N =19.6 G and a Al =1.7 G), respectively ( a N and a Al are constants of hyperfine structure from the corresponding nucleus). According to EPR measurements, concentration of sites I is close to that of sites II, and MAO contains one site of each type per 100±30 aluminium atoms. The adducts of TEMPO with sites I are less stable than those with sites II. Based on the values of a Al and relative stabilities of the adducts with TEMPO, the acidic sites I and II were attributed to coordinatively unsaturated aluminium atoms in AlOMe 2 and AlO 2 Me environment, respectively. From the EPR spectra of coordinated TEMPO, the average radius of MAO oligomers (AlOMe) n was evaluated to be 5.8 A at 20°C, which corresponds to the value of n =15–20. Thus, the major part of MAO contains not more than one Lewis acidic site per one oligomeric (AlOMe) n molecule.

Silica-supported zirconocene catalysts: Preparation, characterization and activity in ethylene polymerization

Abstract Supported catalysts for ethylene polymerization have been prepared by interaction of Cp2ZrX2 (Cp=η5-C5H5, X=Cl or CH3) with silica chemically modified by (CH3)3SiCl (TMCS) or trialkylaluminium compounds AlR3 (R=C2H5 (TEA) and i C 4H9 (TIBA)). The interactions between the modificators and the silica surface have been examined by 1 H solid-state MAS NMR spectroscopy, DRIFTS and chemical analysis. The Cp2Zr(CH3)2/SiO2–TMCS catalyst showed a fairly high activity in ethylene polymerization (30–300 kg PE(mol Zr·h·bar)−1) even in the absence of any cocatalysts specially added. The addition of the cocatalyst (MAO or TIBA) led to a further increase in the activity of the supported catalysts. Polyethylene obtained with the Cp2Zr(CH3)2/SiO2–TMCS catalyst without any cocatalyst consisted of uniform polymer particles of a spherical shape replicating that of the silica particles, whereas the shapeless aggregates of finely dispersed polymer particles similar to those usually obtained with homogeneous systems were produced with the same supported catalyst in the presence of the MAO cocatalyst.

IRS study of ethylene polymerization catalyst SiO2/methylaluminoxane /zirconocene

Abstract IR spectroscopy has been used to study the interaction of silica with two methylaluminoxane (MAO) samples differed by trimethylaluminium (TMA) content and with TMA. MAO and TMA have been shown to react with silica in a different way. Whereas TMA interacts with terminal hydroxyl groups of silica via the protolysis reaction, MAO mainly adsorbs on the surface hydroxyl groups of silica without noticeable protolytical reaction with them. When silica is treated with commercial grade MAO with significant TMA content, the silica surface hydroxyl groups mainly interacts with TMA and MAO adsorbs on the surface of SiO 2 /TMA sample. Lewis acidic sites (LAS) of silica, modified with TMA and MAO samples differed by TMA content, have been investigated by IR spectroscopy (CO adsorption as probe molecule at 77 K). Two types of LAS were found on the surface of silica modified with MAO and TMA: LAS of moderate strength ( ν CO =2204–2212 cm −1 ) and weak LAS ( ν CO =2194 cm −1 ). The concentration of these acidic sites was estimated. By anchoring of Cp 2 ZrCl 2 on silica, modified with TMA and MAO, the corresponding catalysts SiO 2 /TMA/Cp 2 ZrCl 2 and SiO 2 /MAO/Cp 2 ZrCl 2 were prepared and tested at ethylene polymerization. Some correlations between the amount and strength of surface LAS of supports, catalysts composition and their activity are discussed. It is proposed that the surface active species are formed at zirconocene interaction with the most strong LAS.

1H-, 13C-NMR and ethylene polymerization studies of zirconocene/MAO catalysts: effect of the ligand structure on the formation of active intermediates and polymerization kinetics

Abstract Using 1 H- and 13 C-NMR spectroscopies, cationic intermediates formed by activation of L 2 ZrCl 2 with methylaluminoxane (MAO) in toluene were monitored at Al/Zr ratios from 50 to 1000 (L 2 are various cyclopentadienyl (Cp), indenyl (Ind) and fluorenyl (Flu) ligands). The following catalysts were studied: (Cp-R) 2 ZrCl 2 (R=Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , Me 5 , n -Bu, t -Bu), rac-ethanediyl(Ind) 2 ZrCl 2 , rac-Me 2 Si(Ind) 2 ZrCl 2 , rac-Me 2 Si(1-Ind-2-Me) 2 ZrCl 2 , rac-ethanediyl(1-Ind-4,5,6,7-H 4 ) 2 ZrCl 2 , (Ind-2-Me) 2 ZrCl 2 , Me 2 C(Cp)(Flu)ZrCl 2 , Me 2 C(Cp-3-Me)(Flu)ZrCl 2 and Me 2 Si(Flu) 2 ZrCl 2 . Correlations between spectroscopic and ethene polymerization data for catalysts (Cp-R) 2 ZrCl 2 /MAO (R=H, Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , Me 5 , n -Bu, t -Bu) and rac-Me 2 Si(Ind) 2 ZrCl 2 were established. The catalysts (Cp-R) 2 ZrCl 2 /AlMe 3 /CPh 3 + B(C 6 F 5 ) 4 − (R=Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , n -Bu, t -Bu) were also studied for comparison of spectroscopic and polymerization data with MAO-based systems. Complexes of type (Cp-R) 2 ZrMe + ←Me − -Al≡MAO ( IV ) with different [Me-MAO] − counteranions have been identified in the (Cp-R) 2 ZrCl 2 /MAO (R= n -Bu, t -Bu) systems at low Al/Zr ratios (50–200). At Al/Zr ratios of 500–1000, the complex [L 2 Zr(μ-Me) 2 AlMe 2 ] + [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) 2 ZrCl 2 /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) 2 ZrCl 2 /MAO (R=1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 ) and rac-Me 2 Si(Ind) 2 ZrCl 2 /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.

13C-NMR study of Ti(IV) species formed by Cp*TiMe3 and Cp*TiCl3 activation with methylaluminoxane (MAO)

Abstract Using 13 C- and 1 H-NMR spectroscopy, titanium(IV) species formed in the catalytic systems Cp*TiMe 3 /MAO and Cp*TiCl 3 /MAO (Cp*=C 5 (CH 3 ) 5 ) in toluene and chlorobenzene were studied within the temperature range 253–293 K and at Al/Ti ratios 30–300. It was shown that upon activation of Cp*TiMe 3 with methylaluminoxane (MAO) mainly the ‘cation-like’ intermediate Cp*Me 2 Ti + ←Me − Al(MAO) ( 2 ) is formed. Three types of titanium(IV) complexes were identified in Cp*TiCl 3 /MAO catalytic system. They are methylated complexes Cp*TiMeCl 2 and Cp*TiMe 2 Cl, and the ‘cation-like’ intermediate 2 . Complex 2 dominates in Cp*TiCl 3 /MAO system in conditions approaching to those of practical polymerization (Al/Ti ratios more than 200). According to the EPR measurements, the portion of EPR active Ti(III) species in the Cp*TiCl 3 /MAO system is smaller than 1% at Al/Ti=35, and is about 10% at Al/Ti=700.

Cu(II) and Cu(I) complexes with 2-(3,5-diphenyl-1H-pyrazole-1-yl)-4,6-diphenylpyrimidine: Synthesis and structure. Catalytic activity of Cu(II) compounds in reaction of ethylene polymerization

The Cu(II) and Cu(I) complexes with 2-(3,5-diphenyl-1H-pyrazole-1-yl)-4,6-diphenylpyrimidine (L) of the composition CuLX2 (X = Cl, Br) and CuL(MeCN)Br are synthesized. According to X-ray diffraction data, the complexes have molecular structures. The molecules L are coordinated to the copper atom in bidentate-cyclic mode, i.e., through the N2 atom of pyrazole and N1 atom of pyrimidine rings. The coordination polyhedron of the Cu2+ ion in CuLX2 compounds is completed to a distorted tetrahedron with halide ions, that of the Cu+ ion in CuL(MeCN)Br compounds, with the bromide ion and the nitrogen atom of acetonitrile molecule. The CuLX2 complexes (X = Cl, Br) in combination with cocatalysts (methylaluminoxane and triisobutylaluminium) exhibit catalytic activity in ethylene polymerization.

Ethylene Polymerization in the Presence of Iron(II) 2,6-Bis(imine)pyridine Complex: Structures of Key Intermediates

The structures of intermediates generated by the activation of 2,6-bis[1-(2,6-dimethylphenylimino)ethyl]pyridineiron(II) chloride (1) with various cocatalysts, methylalumoxane (MAO), trimethylaluminum (TMA), and TMA in combination with B(C6F5)3and Ph3CB(C6F5)4, is studied by 1H and 2HNMR spectroscopy. The 1/AlMe3system exhibits a higher catalytic activity in ethylene polymerization than the 1/MAO system. The activity of the latter decreases sharply with a decrease in the amount of AlMe3in MAO. Neutral Fe(II) complexes rather than cationic intermediates are suggested to be active components in both catalytic systems.

Formation and evolution of chain-propagating species upon ethylene polymerization with neutral salicylaldiminato nickel(II) catalysts

Formation of Ni-polymeryl propagating species upon the interaction of three salicylaldiminato nickel(II) complexes of the type [(N,O)Ni(CH3 )(Py)] (where (N,O)=salicylaldimine ligands, Py=pyridine) with ethylene (C2 H4 /Ni=10:30) has been studied by (1) H and (13) C NMR spectroscopy. Typically, the ethylene/catalyst mixtures in [D8 ]toluene were stored for short periods of time at +60 °C to generate the [(N,O)Ni(polymeryl)] species, then quickly cooled, and the NMR measurements were conducted at -20 °C. At that temperature, the [(N,O)Ni(polymeryl)] species are stable for days; diffusion (1) H NMR measurements provide an estimate of the average length of polymeryl chain (polymeryl=(C2 H4 )n H, n=6-18). At high ethylene consumptions, the [(N,O)Ni(polymeryl)] intermediates decline, releasing free polymer chains and yielding [(N,O)Ni(Et)(Py)] species, which also further decompose to form the ultimate catalyst degradation product, a paramagnetic [(N,O)2 Ni(Py)] complex. In [(N,O)2 Ni(Py)], the pyridine ligand is labile (with activation energy for its dissociation of (12.3±0.5) kcal mol(-1) , ΔH(≠) 298 =(11.7±0.5) kcal mol(-1) , ΔS(≠) 298 =(-7±1) cal K(-1)  mol(-1) ). Upon the addition of nonpolar solvent (pentane), the pyridine ligand is lost completely to yield the crystals of diamagnetic [(N,O)2 Ni] complex. NMR spectroscopic analysis of the polyethylenes formed suggests that the evolution of chain-propagating species ends up with formation of polyethylene with predominately internal and terminal vinylene groups rather than vinyl groups.

Cobalt(II) and copper(II) complexes with chiral pyrazolylquinoline, a derivative of terpenoid (+)-3-carene. Catalytic activity in ethylene polymerization reaction

Coordination compounds [CoLCl2] (I), [CuLCl(NO3)] (II), CuL(NO3)2 (III), and CuLCl2 (IV) (where L is a chiral pyrazolylquinoline—a derivative of terpenoid (+)-3-carene) were synthesized. X-ray diffraction data showed that crystal structures I and II are built of mononuclear acentric molecules. In the molecule of complex I, the Co2+ ion coordinates two N atoms of bidentate cycle-forming ligand L and two Cl atoms. The coordination polyhedron of Cl2N2 is a distorted tetrahedron. For complex I, μeff = 4.50 μB, which corresponds to a high-spin configuration d7. In the molecules of II(1), II(2) (which are diastereoisomers of complex II), each Cu2+ ion coordinates two N atoms of bidentate cycle-forming ligand L, the Cl atom, and two O atoms of bidentate cyclic NO3− ion. The ClN2O2 coordination polyhedra are tetragonal pyramids with different degrees of distortion. The structure of complex II consists of supramolecular clusters, i.e., isolated chains incorporating the molecules of II(1) and II(2). The values of μeff for II–IV correspond to the d9 configuration. The results of EPR and IR study suggest that complex III contains the O4N2 polyhedron, whereas complex IV contains the Cl2N2 polyhedron. Complexes I and IV were found to show a high catalytic activity in ethylene polymerization reaction.