Iron and Cobalt Complexes of Tridentate N-Donor Ligands in Ethylene Polymerization: Efficient Shielding of the Active Sites by Simple Phenyl Groups (original) (raw)
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Macromolecular Research, 2005
A series of ethylene polymerization catalysts based on tridentate bis-imine ligands coordinated to iron and cobalt was reported. The ligands were prepared through the condensation of sterically bulky anilines with allyloxy-and benzyloxy-substituted 2,6-acetylpyridines. The pre-catalyst complexes were penta-coordinate species of the general formula {[(ArN=C(Me)) 2 (4-RO-C 5 H 3 N)]MCl 2 } (Ar=ortho dialkyl-substituted aryl ring; R=allyl, benzyl; M=Fe, Co). In the presence of ethylene and methyl alumoxane cocatalysts, these complexes were active for the polymerization of ethylene, with activities lower than those of metal complexes of the general formula {[(2-ArN= C(Me)) 2 C 5 H 3 N]MCl 2 } (Ar=ortho dialkyl-substituted aryl ring; M=Co, Fe), containing no substituents in 2,6acetylpyridine ring. The effects of the catalyst structure and temperature on the polymerization activity, thermal properties, and molecular weight were discussed.
Applied Catalysis A: General, 2005
The complexes Py(PzR 3 ) 2 MCl 2 (R = H, Me; M = Fe, Co) and Py(CH 2 -PzR 3 ) 2 MCl 2 (R = H, Me; M = Fe, Co) have been synthesized, characterized and used in the ethylene polymerization. Treatment of these iron and cobalt complexes with methylaluminoxane (MAO) as cocatalyst leads to active ethylene polymerization catalysts that produced linear polyethylene. In general, iron catalysts were more active than cobalt analogs. The steric and electronic effects of the ligands were study over the catalytic activity toward ethylene polymerization. Complexes with small substituents groups (R = H) on the pyrazolyl ring, increase the catalytic activity in comparison to complexes with bigger substituents groups (R = CH 3 ). Additionally, complexes with methylene groups placed between pyridine and pyrazole rings of ligands have less catalytic activity than complexes without the methylene group (-CH 2 -). The presence of methyl groups (R = CH 3 ) in iron and cobalt complexes allow to obtain polyethylene with molecular weights higher than the one obtained with complexes without these methyl groups. Additionally, complexes with methylene groups present between pyridine and pyrazole rings generate polyethylenes with molecular weight higher than the ones produced with complexes without these methylene groups. #
Iron and Cobalt Ethylene Polymerization Catalysts: Variations on the Central Donor
Inorganic Chemistry, 2003
Three classes of ligands, designed to explore the effect of variations on the central pyridine donor core in bis-(imino)pyridine iron and cobalt ethylene polymerization catalysts of the general formula [LMCl 2 ] (M) Fe or Co), have been prepared. The first class comprises six-membered N-heterocycles (pyrimidine and triazine) and the second class five-membered heterocycles (furan and thiophene) as the central donor core. In the third class of ligands, the imine donor arm has been extended by one carbon to give anionic tridentate ligands based on carbazole and neutral analogues based on dibenzofuran and dibenzothiophene. The coordination behavior of these ligands upon reaction with FeCl 2 or CoCl 2 has been investigated, whereby only in the case of the neutral pyrimidine or the anionic carbazolide unit as the central donor core have stable complexes been obtained. Ethylene polymerization results are compared with the parent bis(imino)pyridine iron and cobalt catalyst systems.
European Polymer Journal, 2005
In the present paper, the synthesis of new pyridine bis(imine) ligands modified with halogens (Cl, Br, CF 3 ) or alkyl groups (Heptyl, tert-butyl, Phenyl, . . .) is reported. When coordinated with iron or cobalt dichloride, they yielded complexes which were associated to methylaluminoxane (MAO) to achieve the polymerization of ethylene. It was shown that cobalt catalysts are generally more sensitive to the ligand substitutions than the iron ones. The addition of a chlorine atom on the ligand frame is generally unfavorable. On the contrary, the presence of a bromine atom seems more favorable. Phenyl rings lead to almost completely inactive catalysts, probably because of a too weak coordination to the metal. It was also demonstrated that a mono-substitution of the aryl groups with an electron-withdrawing group (-CF 3 ) is sufficient to yield polymers, whereas, considering the bulkiness of this substituent only, oligomers would have been expected.
N-Pyrrolyl-[N,N,N]-bis(imino)pyridyl iron(II) and cobalt(II) olefin polymerization catalysts
Applied Organometallic Chemistry, 2002
A series of new [N,N,N] 2,6-bis(imino)pyridyl iron and cobalt halide complexes as precatalysts for the homo-and co-polymerization of ethylene has been synthesized and evaluated for their catalytic performance. The novel key structural feature of these [N,N,N]MCl 2 catalysts is their peripheral substitution with bulky N-heterocyclic groups, including substituted N-pyrrolyl, N-indolyl, Ncarbazolyl, and N-triazolyl moieties. The synthesis starts with the corresponding N-amino-Nheterocycles, which were prepared by a modified Paal±Knorr condensation of 1,4-diketones with mono-protected hydrazines, or by electrophilic amination of benzannelated azoles. Condensation with 2,6-diacetylpyridine or 2,5-diformylthiophene afforded 14 different terdentate ligands, and complex formation with iron(II), iron(III), cobalt(II) yielded 23 different precatalysts. A single crystal structure analysis of one representative showed that these paramagnetic complexes have a distorted trigonal bipyramidal structure with orthogonal sterically shielding N-azolyl groups. All the methylalumoxane-activated iron(II) and cobalt(II) complexes with N-pyrrolyl, N-indolyl, and Ncarbazolyl substituents are highly active catalysts for the homo-and co-polymerization of ethylene, producing polymers with comparatively narrow molecular weight distributions and with a wide range of molecular weights, dependent on the substitution pattern of the peripheral N-azolyl substituents. The observed microstructures of the polymers vary from very highly branched to mostly linear, giving access to oligomers and polymers with an unusual broad spectrum of macroscopic physical properties.
European Journal of Inorganic Chemistry, 2006
In this paper, we describe the synthesis of two new pyridinebis(imine)s {4-chloro-2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine and 2,6-bis[1-(2,6-dimethylcyclohexylimino)ethyl]pyridine} and their complexation with iron and cobalt dichloride. The solid-state structure of the iron complexes was solved and found to be very close to catalysts already described by Brookhart and Gibson. Their ability to polymerize ethylene was investigated after activation with MAO. It was thus shown that the substitution of the pyridine ring of [a]
Bis(imino)pyridine–iron(II) complexes for ethylene polymerization
Polymer Science, Series B
Ethylene polymerization was carried out using new late transition metal 2,6-bis(imino)pyridine catalysts containing different substituents (H, NO 2 , and OCH 3) at the para position of the pyridine ring, activated by methylaluminoxane. Effects of polymerization parameters such as ethylene pressure, reaction temperature, hydrogen concentration and structure variation on the catalysts activities and polymer properties were investigated. Introducing the functionality in the para-position of the pyridine ring of the catalysts had remarkable effect on the polymer properties as well as the catalysts activities.
Journal of Organometallic Chemistry, 2007
An adaptable synthetic methodology for the tridentate dianionic pyridine-2-phenolate-6-aryl [O,N,C] ligand framework, comprising the aromatic r-carbanion moiety as a chelating component, has been developed. A series of non-fluorinated group 4 bis(benzyl) complexes supported by [O,N,C] auxiliaries, with halogen and alkyl groups at the 'R 1 ' position ortho to the metal-C(r-aryl) bond, have been prepared by exploiting the cyclometalation of the ligand. All derivatives have been characterized by NMR spectroscopy, and the spectral features concerning the metal-bound diastereotopic methylene groups have been highlighted. The capabilities of these complexes as catalysts for olefin polymerization have been tested, and comparisons with the recently reported fluorine-containing Ti-[O,N,C] analogues and related Hf-[N,N,C] derivatives are discussed. The titanium catalysts, in conjunction with MAO, displayed moderate to high activities for ethylene polymerization (up to 200 g mmol À1 h À1).
Journal of Organometallic Chemistry, 2015
New (pyrazolyl)-(phosphinoyl)pyridine ligands 2-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-6-((diphenylphosphinoyl)methyl)pyridine (L1b) and 2-((3,5-diphenyl-1H-pyrazol-1-yl)methyl)-6-((diphenylphosphinoyl)methyl)pyridine (L2b) were synthesized in high yields. Reactions of L1b and L2b with Fe(II), Co(II) and Ni(II) salts afforded complexes [NiCl 2 (L1b)] (1), [NiBr 2 (L1b)] (2), [CoCl 2 (L1b)] (3), [FeCl 2 (L1b)] (4), [NiBr 2 (L2b)] (5), and [CoCl 2 (L2b)] (6) in good yields. The compounds were characterized by NMR spectroscopy, mass spectrometry and elemental analyses. Molecular structures of complexes 1, 5 and 6 were confirmed by single crystal X-ray crystallography to contain one tridentate bound N^N^O L1b and L2b ligands. Complexes 1e6 formed active catalysts in ethylene oligomerization reactions upon activation with EtAlCl 2 , methylaluminoxane (MAO) or trimethylaluminium (AlMe 3) as co-catalyst to produce C 4 as the major product as well as C 6 and C 8 oligomers. The nature of solvent and co-catalyst, significantly affected both the activities and product compositions of the resultant catalysts.