Victoria Volkis - Academia.edu (original) (raw)
Papers by Victoria Volkis
Journal of The American Chemical Society, 2009
In the presence of LiCB(11)Me(12) catalyst and a nonoxidizing radical initiator, isobutylene unde... more In the presence of LiCB(11)Me(12) catalyst and a nonoxidizing radical initiator, isobutylene undergoes radical chain polymerization in an inert solvent at ambient temperature and pressure to give a new highly branched form of polyisobutylene. Copolymerization with ethyl acrylate is also possible.
Macromolecules, 2011
The radical homopolymerization of isobutylene (IB) is unusual but can be accomplished under catal... more The radical homopolymerization of isobutylene (IB) is unusual but can be accomplished under catalysis with LiCB 11 (CH 3 ) (1) in poorly coordinating solvents at ambient pressure and temperature. 1-3 It yields a novel highly branched form of polyisobutylene (b-PIB) with molecular weights in the thousands (up to ∼2.5 Â 10 4 ) according to GPC relative to polystyrene standards. Presently we examine the use of the LiCB 11 (CH 3 ) 12 catalyst with azo-tertbutane (ATB) radical initiator for the copolymerization of IB with ethyl acrylate (EA), as previously briefly mentioned in a short communication. We find that it leads to an unusual somewhat branched nonalternating high molecular weight copolymer with up to ∼56 mol % of IB.
Radical polymerization of selected 1-alkenes, (1-hexene, 1-octene and 2-methyl-1-heptene), initia... more Radical polymerization of selected 1-alkenes, (1-hexene, 1-octene and 2-methyl-1-heptene), initiated with classical radical initiators and catalyzed by lithium salts of selected carboranes was studied. In accordance with recently published results it was found that the use of radical initiators under catalysis by ''naked'' lithium cation of carboranes promotes the radical polymerization of 1-alkenes, otherwise nonpolymerizable by the radical mechanism. However, although in our experiments rela-tively high monomers conversions are reached for some of the thermal initiators used, only low-molecular-weight oligomers with M n < 1000 are formed, regardless of the initiator and carborane anion used.
European Journal of Inorganic Chemistry, 2006
The ansa-indene ligands {1-Me2Si(3-C9H6R)2} [R = Me (1), nPr (2), nBu (3), and Bz (4)] were prepa... more The ansa-indene ligands {1-Me2Si(3-C9H6R)2} [R = Me (1), nPr (2), nBu (3), and Bz (4)] were prepared by alkylation of the unsubstituted ansa-indene. These ligands were converted, by reaction with nBuLi, to the di-lithium compounds [Li2{1-Me2Si(3-C9H5R)2}] [R = Me (5), nPr (6), nBu (7), and Bz (8)]. ansa-Zirconocenes, [Zr{1-Me2Si(3-η5-C9H5R)2}Cl2] [R = Me (9), nPr (10), nBu (11), and Bz (12)], have been prepared by the reaction of ZrCl4 with 5–8 in diethyl ether/toluene at–78 °C. The molecular structure of meso-[Zr{1-Me2Si[3-η5-C9H5(CH3)]2}Cl2] (9) and rac-[Zr{1-Me2Si[3-η5-C9H5(CH2CH2CH3)]2}Cl2] (10) have been determined by single-crystal X-ray diffraction studies. Ethylene polymerization catalysis has been studied for complexes 9–12 as a mixture of meso and rac isomers in the presence of methylaluminoxane (MAO) as cocatalyst. Complexes 9–12 exhibit high activities and give rise to polyethylene with low molecular weights without the introduction of molecular hydrogen. In addition, active species from these complexes were found to be very stable in comparison with unsubstituted analogues.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Israel Journal of Chemistry, 2002
The polymerization of ethylene and propylene were studied using an anchored dimethyl benzamidinat... more The polymerization of ethylene and propylene were studied using an anchored dimethyl benzamidinate zirconium complex. As supports, mesoporous silicas MCM-41 and HMS were utilized. These inorganic materials were reacted with methylalumoxane to serve as the cocatalyst and to avoid the deactivation of the active cationic complex. The reaction of the octahedral benzamidinate zirconium complex with the supported cocatalysts results in the formation of active catalytic systems for the polymerization of olefins. The polymer properties were found to depend on the nature of the supports. The activity of the heterogeneous catalysts and the polymer characteristics were compared with those obtained with the homogeneous catalyst.
Organometallics, 1998
This communication reports the synthesis and activity of four racemic mixtures of bis (benzamidin... more This communication reports the synthesis and activity of four racemic mixtures of bis (benzamidinate) group-4 complexes, cis-[p-R′C 6 H 4 ) as precatalysts for the stereoregular polymerization of propylene. These complexes catalyze the stereoregular polymerization of propylene only under pressure in CH 2 Cl 2 , producing polypropylene with very large isotacticities (mmmm % ) ∼95-98), high melting points (140-154°C ).
Inorganica Chimica Acta, 2002
Methylalumoxane (MAO) is an active pre-catalyst for the polymerization of isobutylene and the cop... more Methylalumoxane (MAO) is an active pre-catalyst for the polymerization of isobutylene and the copolymerization of isobutylene with isoprene at ambient temperature. The absence of any proton-containing substances suggests that the solvent dichloromethane reacts with the MAO forming the active cationic species. In the presence of toluene, as the solvent, the reaction rate is extremely low. The increase of the MAO concentration in the reaction mixture causes a large increase in the isobutylene conversion, although the molecular weight of the polymers sharply decreases. The use of CD 2 Cl 2 as a solvent induces a large kinetic isotope effect (KIE 0/7). In the copolymerization of isobutylene with large amounts of isoprene a cross-linkage copolymer is formed. The polymerization and copolymerization reactions were also studied in the presence of a mixture of MAO with the complex (acac) 2 TiCl 2 (acac 0/ acetylacetonate). # (M.S. Eisen).
Acta Crystallographica Section A, 2002
Macromolecular Research, 2010
A new epimerization mechanism was introduced for the polymerization of propylene obtained by octa... more A new epimerization mechanism was introduced for the polymerization of propylene obtained by octahedral benzamidinate complexes. Deuterium labeling showed that deuterium is transferred from a methyne to a methylene position in the polymer inducing a stereoerror and an elastic material. In addition, two active species are formed during the polymerization of propylene promoted by the octahedral bis(benzamidinate) titanium dialkyl complexes.
Polyhedron, 2005
The following ansa-ligand precursors, Et(H)Si(C 5 H 5 ) 2 (1), Et(H)Si(C 5 } (15) have been prepa... more The following ansa-ligand precursors, Et(H)Si(C 5 H 5 ) 2 (1), Et(H)Si(C 5 } (15) have been prepared. The group 4 metal complexes, [M{Et(H)Si(g 5 -C 5 H 4 ) 2 }Cl 2 ] (M = Ti (16a), Zr (16b), Hf (16c)), [M{Et(H)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (M = Ti (17a), Zr (17b), Hf (17c)), [M{Ph(H)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (M = Ti (18a), Zr (18b), Hf (18c)), [M{Ph(H)Si(g 5 -C 5 Me 4 ) 2 }Cl 2 ] (M = Ti (19a), Zr (19b), Hf (19c)), M{CH 2 @CHCH 2 (H)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (M = Ti (20a), Zr (20b)) and [M{CH 2 @CHCH 2 (H)Si(g 5 -C 5 Me 4 ) 2 }Cl 2 ] (M = Ti (21a), Zr (21b), Hf (21c)) were synthesized from the reaction of the lithium ansa-derivatives and the tetrachloride salts of the transition metal. The reactivity of the group 4 metal complexes in hydrosilylation processes has been studied. The reaction of 16b, 17a and 17b with tetravinylsilane gave [Zr{(CH 2 @CH) 3 SiCH 2 CH 2 (Et)Si(g 5 -C 5 H 4 ) 2 }Cl 2 ] (22b) and [M{(CH 2 @CH) 3 SiCH 2 CH 2 (Et)-Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (M = Ti (23a), Zr (23b)), respectively. The reaction of 17a and 17b with dimethyldivinylsilane yielded the hydrosilylation products [M{(CH 2 @CH)Me 2 SiCH 2 CH 2 (Et)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (M = Ti (24a), Zr (24b)), respectively. 23b and 24b reacted with the silane reagent HSiEt 3 to form, via hydrosilylation, [Zr{(Et 3 SiCH 2 CH 2 ) 3 SiCH 2 CH 2 (Et)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (25b) and [Zr{(Et 3 SiCH 2 CH 2 )Me 2 SiCH 2 CH 2 (Et)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (26b), respectively.
Polymers for Advanced Technologies, 2002
This study reports the synthesis and activity as precatalysts for the polymerization of propylene... more This study reports the synthesis and activity as precatalysts for the polymerization of propylene of five racemic group 4 complexes, cis-[p-R′C6H4C(NR)2]2MX2 (R′ = CH3, R = SiMe3, M = Ti, X = Cl (1); R′ = CH3, R = SiMe3, M = Zr, X = Cl (2); R′ = H, R = i-pr, M = Zr, X = Cl (3); R′ = CH3, R = SiMe3, M = Zr, X = CH3 (4)) and (acac)2MCl2 (M = Ti (5), M = Zr (6)) (acac = acetylacetone). The hydrocarbyl complex 4 was prepared by the alkylation of the corresponding complex 2 with MeLi·LiBr. Reaction of complex 4 with B(C6F5)3 or all complexes with MAO (MAO = methylalumoxane) results in the formation of a “cationic” intermediate complex which rapidly reacts with the incoming monomer. Some of the complexes catalyze the stereoregular polymerization of propylene only under pressure in either toluene or CH2Cl2, producing polypropylene with very large isotacticities (mmmm % = ∼95–98), high melting points (140–154 °C) and similar molecular weights as compared with cyclopentadienyl complexes, whereas complex 5 is active for the polymerization of elastomeric polypropylene. Copyright © 2003 John Wiley & Sons, Ltd.
Studies in Surface Science and Catalysis, 2006
The influence of the number of ancillary ligations and the corresponding structural features of t... more The influence of the number of ancillary ligations and the corresponding structural features of three titanium benzamidinate complexes 1–3, in the polymerization of propylene, has been investigated. These complexes produce similar polymers indicating the formation of similar active species. The activation process was followed via 29Si-NMR spectroscopy.
Organometallics, 2006
ABSTRACT
Organometallics, 2006
A new mechanism for the formation of stereoerrors during the polymerization of propylene, promote... more A new mechanism for the formation of stereoerrors during the polymerization of propylene, promoted by the C 2symmetric benzamidinate titanium complex 1, has been obserVed at low and high pressure using unlabeled and 2-d-labeled propylene. The use of deuterated propylene induces higher tacticities and molecular weights of the resulting polymers. At high pressure, the polymerization of the deuterated propylene induces faster insertion and termination processes. The new epimerization mechanism, which may be accompanied by a CH 2 / CD(Me) exchange, is presented.
Journal of Polymer Science Part A-polymer Chemistry, 2005
The effect of solvents (toluene, dichloromethane, and hexane) was studied on the polymerization o... more The effect of solvents (toluene, dichloromethane, and hexane) was studied on the polymerization of propylene with the octahedral complexes bis(trimethylsilyl)benzamidinate titanium dichloride(a), bis(acetylacetonate) titanium dichloride(b), and bis(diethylamino) titanium di-2-(diphenylphosphanylamino)pyridine as catalytic precursors and methylalumoxane as the cocatalyst. For comparison, the polymerization was also performed in plain liquid propylene without the addition of any solvent. The obtained polymers were fractionated by refluxing hexane. The activity of the complexes and the molecular weights and tacticities of the whole polymers and their different fractions were the studied parameters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4505–4516, 2005
Journal of The American Chemical Society, 2003
The synthesis and structural X-ray diffraction studies for some benzamidinate ligations and sever... more The synthesis and structural X-ray diffraction studies for some benzamidinate ligations and several group 4 benzamidinate complexes are presented. The use of the cis-octahedral C(2)-symmetry compounds was studied to shed light on the conceptual applicability of these complexes as potential catalysts for the stereoregular polymerization of propylene. We demonstrate that the stereoregular polymerization of propylene catalyzed by early-transition metal octahedral benzamidinate complexes, activated with either MAO or B(C(6)F(5))(3) as cocatalysts, can be modulated by pressure (from atactic to isotactic through elastomers). The different effects in the polymerization process such as the nature of solvent or cocatalyst, temperature, pressure, molar ratio catalyst:cocatalyst, and the relationship between the symmetry of the complex and the polymer microstructure have been investigated. When the complex [4-CH(3)-C(6)H(4)C(NTMS)(2)](2)ZrMe(2) (9) was activated with MAO, it was found to be a good catalyst for the polymerization of propylene, at atmospheric pressure, producing an oily polymer resembling an atactic polypropylene. Being activated with B(C(6)F(5))(3), complex 9 produces a highly isotactic (mmmm = 98%) product. Likewise, when the polymerization of propylene was performed with complex 9 and MAO at high pressure (liquid propylene), a highly stereoregular polymer was also obtained. Larger activities and stereoregularities were achieved by performing the reaction in CH(2)Cl(2) as compared to toluene. Contrary to complex 9, at atmospheric pressure the complex [4-CH(3)-C(6)H(4)C(NTMS)(2)](2)TiMe(2) (10) is not active either in CH(2)Cl(2) or in toluene. At high pressure, complex 10 produces elastomeric polypropylene. Activities of the isolobal complexes [C(6)H(4)C(NTMS)(2)](2)ZrMe(2) (11) and [C(6)H(4)C(NTMS)(2)](2)TiMe(2) (12) were found to be larger than those of complexes 9 and 10, respectively. Contrary to the structures of the elastomeric polypropylenes described in the literature, the obtained elastomers are characterized by frequent alternation of the isotactic domains with stereodefects. The stereoregular errors are formed by the intramolecular epimerization of the growing chain at the last inserted unit. The epimerization reaction was corroborated through the isomerization of alkenes.
Organometallics, 2006
The zirconium benzamidinate dimethyl complex [PhC(NSiMe 3 ) 2 ] 2 Zr(Me) 2 (1) was actiVated by a... more The zirconium benzamidinate dimethyl complex [PhC(NSiMe 3 ) 2 ] 2 Zr(Me) 2 (1) was actiVated by a mixture of trityl tetrakispentafluorophenylborate (TTPB) and a small amount of methylalumoxane (MAO) (Zr:B:Al ) 1:1:50), forming an extremely actiVe catalytic system for the polymerization of olefins, producing high-density polyethylene and elastomeric polypropylene with a narrow MWD. This catalytic system riVals the actiVity of the best nonmetallocene systems and approaches the actiVities of the best metallocene complexes. Single actiVe sites are obtained only after the addition of propylene. A plausible actiVation mechanism is proposed, which is corroborated by NMR, ESR spectroscopy, radical trapping on fullerene, and MALDI-TOF mass spectroscopy experiments.
Journal of Organometallic Chemistry, 2007
Zirconium and titanium bis(benzamidinate) dimethyl complexes were found to be active catalytic pr... more Zirconium and titanium bis(benzamidinate) dimethyl complexes were found to be active catalytic precursors for the oligomerization of mono-and bis-substituted silanes. The activation of such complexes, by an excess of MAO or by an equimolar amount of B(C 6 F 5 ) 3 , increases the catalytic activity of the complexes and the molecular weight of the obtained oligosilanes. The maximum polymerization index that was accomplished (n = 90) is by far the largest obtained with other organometallic complexes. In addition, the activated benzamidinate catalysts were also found to be active for the polymerization of 1,5-hexadiene producing poly(methyl-1,3-cyclopentane). For the latter, the results obtained with C 2 -symmetry bis(benzamidinate) dimethyl complexes were compared with a chiral complex bearing a myrtanyl group at the benzamidinate ligand.
Journal of Organometallic Chemistry, 2008
The reaction of Li2[1,2-{N(PMes2)}2C6H4], formed in situ from n-BuLi and the corresponding amines... more The reaction of Li2[1,2-{N(PMes2)}2C6H4], formed in situ from n-BuLi and the corresponding amines, with 1equiv. of [NiBr2(DME)] gives [Ni{1-N(PMes2)-2-N(μ-PMes2)C6H4-κ3N,N′,P-κ1P′}]2 (1). After activation by methylalumoxane (MAO), 1 is a highly active catalyst in the oligomerization and isomerization of α-olefins such as ethene, propene, isobutene, 1-hexene and 1,5-hexadiene. For ethene oligomerization turnover frequencies (TOFs) range from 3000 to 79015h−1, depending on the
Macromolecular Symposia, 2007
A series of dimethyl titanium benzamidinate complexes has been prepared containing various functi... more A series of dimethyl titanium benzamidinate complexes has been prepared containing various functional groups at the aromatic ring. These functional groups were selected to study their electronic or steric effects at the cationic metal center in the polymerization of propylene. Quantitative structure activity relationship (QSAR) studies showed that a linear relationship is observed only for the Taft Parameter (Es). Mono-and bis-benzamidinate complexes were found to produce similar polymers indicating that alike active species are obtained regardless of the starting complex. Deuterium labeled 2-D-propene showed that a new epimerization mechanism for this type of complexes is operative.
Journal of The American Chemical Society, 2009
In the presence of LiCB(11)Me(12) catalyst and a nonoxidizing radical initiator, isobutylene unde... more In the presence of LiCB(11)Me(12) catalyst and a nonoxidizing radical initiator, isobutylene undergoes radical chain polymerization in an inert solvent at ambient temperature and pressure to give a new highly branched form of polyisobutylene. Copolymerization with ethyl acrylate is also possible.
Macromolecules, 2011
The radical homopolymerization of isobutylene (IB) is unusual but can be accomplished under catal... more The radical homopolymerization of isobutylene (IB) is unusual but can be accomplished under catalysis with LiCB 11 (CH 3 ) (1) in poorly coordinating solvents at ambient pressure and temperature. 1-3 It yields a novel highly branched form of polyisobutylene (b-PIB) with molecular weights in the thousands (up to ∼2.5 Â 10 4 ) according to GPC relative to polystyrene standards. Presently we examine the use of the LiCB 11 (CH 3 ) 12 catalyst with azo-tertbutane (ATB) radical initiator for the copolymerization of IB with ethyl acrylate (EA), as previously briefly mentioned in a short communication. We find that it leads to an unusual somewhat branched nonalternating high molecular weight copolymer with up to ∼56 mol % of IB.
Radical polymerization of selected 1-alkenes, (1-hexene, 1-octene and 2-methyl-1-heptene), initia... more Radical polymerization of selected 1-alkenes, (1-hexene, 1-octene and 2-methyl-1-heptene), initiated with classical radical initiators and catalyzed by lithium salts of selected carboranes was studied. In accordance with recently published results it was found that the use of radical initiators under catalysis by ''naked'' lithium cation of carboranes promotes the radical polymerization of 1-alkenes, otherwise nonpolymerizable by the radical mechanism. However, although in our experiments rela-tively high monomers conversions are reached for some of the thermal initiators used, only low-molecular-weight oligomers with M n < 1000 are formed, regardless of the initiator and carborane anion used.
European Journal of Inorganic Chemistry, 2006
The ansa-indene ligands {1-Me2Si(3-C9H6R)2} [R = Me (1), nPr (2), nBu (3), and Bz (4)] were prepa... more The ansa-indene ligands {1-Me2Si(3-C9H6R)2} [R = Me (1), nPr (2), nBu (3), and Bz (4)] were prepared by alkylation of the unsubstituted ansa-indene. These ligands were converted, by reaction with nBuLi, to the di-lithium compounds [Li2{1-Me2Si(3-C9H5R)2}] [R = Me (5), nPr (6), nBu (7), and Bz (8)]. ansa-Zirconocenes, [Zr{1-Me2Si(3-η5-C9H5R)2}Cl2] [R = Me (9), nPr (10), nBu (11), and Bz (12)], have been prepared by the reaction of ZrCl4 with 5–8 in diethyl ether/toluene at–78 °C. The molecular structure of meso-[Zr{1-Me2Si[3-η5-C9H5(CH3)]2}Cl2] (9) and rac-[Zr{1-Me2Si[3-η5-C9H5(CH2CH2CH3)]2}Cl2] (10) have been determined by single-crystal X-ray diffraction studies. Ethylene polymerization catalysis has been studied for complexes 9–12 as a mixture of meso and rac isomers in the presence of methylaluminoxane (MAO) as cocatalyst. Complexes 9–12 exhibit high activities and give rise to polyethylene with low molecular weights without the introduction of molecular hydrogen. In addition, active species from these complexes were found to be very stable in comparison with unsubstituted analogues.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Israel Journal of Chemistry, 2002
The polymerization of ethylene and propylene were studied using an anchored dimethyl benzamidinat... more The polymerization of ethylene and propylene were studied using an anchored dimethyl benzamidinate zirconium complex. As supports, mesoporous silicas MCM-41 and HMS were utilized. These inorganic materials were reacted with methylalumoxane to serve as the cocatalyst and to avoid the deactivation of the active cationic complex. The reaction of the octahedral benzamidinate zirconium complex with the supported cocatalysts results in the formation of active catalytic systems for the polymerization of olefins. The polymer properties were found to depend on the nature of the supports. The activity of the heterogeneous catalysts and the polymer characteristics were compared with those obtained with the homogeneous catalyst.
Organometallics, 1998
This communication reports the synthesis and activity of four racemic mixtures of bis (benzamidin... more This communication reports the synthesis and activity of four racemic mixtures of bis (benzamidinate) group-4 complexes, cis-[p-R′C 6 H 4 ) as precatalysts for the stereoregular polymerization of propylene. These complexes catalyze the stereoregular polymerization of propylene only under pressure in CH 2 Cl 2 , producing polypropylene with very large isotacticities (mmmm % ) ∼95-98), high melting points (140-154°C ).
Inorganica Chimica Acta, 2002
Methylalumoxane (MAO) is an active pre-catalyst for the polymerization of isobutylene and the cop... more Methylalumoxane (MAO) is an active pre-catalyst for the polymerization of isobutylene and the copolymerization of isobutylene with isoprene at ambient temperature. The absence of any proton-containing substances suggests that the solvent dichloromethane reacts with the MAO forming the active cationic species. In the presence of toluene, as the solvent, the reaction rate is extremely low. The increase of the MAO concentration in the reaction mixture causes a large increase in the isobutylene conversion, although the molecular weight of the polymers sharply decreases. The use of CD 2 Cl 2 as a solvent induces a large kinetic isotope effect (KIE 0/7). In the copolymerization of isobutylene with large amounts of isoprene a cross-linkage copolymer is formed. The polymerization and copolymerization reactions were also studied in the presence of a mixture of MAO with the complex (acac) 2 TiCl 2 (acac 0/ acetylacetonate). # (M.S. Eisen).
Acta Crystallographica Section A, 2002
Macromolecular Research, 2010
A new epimerization mechanism was introduced for the polymerization of propylene obtained by octa... more A new epimerization mechanism was introduced for the polymerization of propylene obtained by octahedral benzamidinate complexes. Deuterium labeling showed that deuterium is transferred from a methyne to a methylene position in the polymer inducing a stereoerror and an elastic material. In addition, two active species are formed during the polymerization of propylene promoted by the octahedral bis(benzamidinate) titanium dialkyl complexes.
Polyhedron, 2005
The following ansa-ligand precursors, Et(H)Si(C 5 H 5 ) 2 (1), Et(H)Si(C 5 } (15) have been prepa... more The following ansa-ligand precursors, Et(H)Si(C 5 H 5 ) 2 (1), Et(H)Si(C 5 } (15) have been prepared. The group 4 metal complexes, [M{Et(H)Si(g 5 -C 5 H 4 ) 2 }Cl 2 ] (M = Ti (16a), Zr (16b), Hf (16c)), [M{Et(H)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (M = Ti (17a), Zr (17b), Hf (17c)), [M{Ph(H)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (M = Ti (18a), Zr (18b), Hf (18c)), [M{Ph(H)Si(g 5 -C 5 Me 4 ) 2 }Cl 2 ] (M = Ti (19a), Zr (19b), Hf (19c)), M{CH 2 @CHCH 2 (H)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (M = Ti (20a), Zr (20b)) and [M{CH 2 @CHCH 2 (H)Si(g 5 -C 5 Me 4 ) 2 }Cl 2 ] (M = Ti (21a), Zr (21b), Hf (21c)) were synthesized from the reaction of the lithium ansa-derivatives and the tetrachloride salts of the transition metal. The reactivity of the group 4 metal complexes in hydrosilylation processes has been studied. The reaction of 16b, 17a and 17b with tetravinylsilane gave [Zr{(CH 2 @CH) 3 SiCH 2 CH 2 (Et)Si(g 5 -C 5 H 4 ) 2 }Cl 2 ] (22b) and [M{(CH 2 @CH) 3 SiCH 2 CH 2 (Et)-Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (M = Ti (23a), Zr (23b)), respectively. The reaction of 17a and 17b with dimethyldivinylsilane yielded the hydrosilylation products [M{(CH 2 @CH)Me 2 SiCH 2 CH 2 (Et)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (M = Ti (24a), Zr (24b)), respectively. 23b and 24b reacted with the silane reagent HSiEt 3 to form, via hydrosilylation, [Zr{(Et 3 SiCH 2 CH 2 ) 3 SiCH 2 CH 2 (Et)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (25b) and [Zr{(Et 3 SiCH 2 CH 2 )Me 2 SiCH 2 CH 2 (Et)Si(g 5 -C 5 Me 4 )(g 5 -C 5 H 4 )}Cl 2 ] (26b), respectively.
Polymers for Advanced Technologies, 2002
This study reports the synthesis and activity as precatalysts for the polymerization of propylene... more This study reports the synthesis and activity as precatalysts for the polymerization of propylene of five racemic group 4 complexes, cis-[p-R′C6H4C(NR)2]2MX2 (R′ = CH3, R = SiMe3, M = Ti, X = Cl (1); R′ = CH3, R = SiMe3, M = Zr, X = Cl (2); R′ = H, R = i-pr, M = Zr, X = Cl (3); R′ = CH3, R = SiMe3, M = Zr, X = CH3 (4)) and (acac)2MCl2 (M = Ti (5), M = Zr (6)) (acac = acetylacetone). The hydrocarbyl complex 4 was prepared by the alkylation of the corresponding complex 2 with MeLi·LiBr. Reaction of complex 4 with B(C6F5)3 or all complexes with MAO (MAO = methylalumoxane) results in the formation of a “cationic” intermediate complex which rapidly reacts with the incoming monomer. Some of the complexes catalyze the stereoregular polymerization of propylene only under pressure in either toluene or CH2Cl2, producing polypropylene with very large isotacticities (mmmm % = ∼95–98), high melting points (140–154 °C) and similar molecular weights as compared with cyclopentadienyl complexes, whereas complex 5 is active for the polymerization of elastomeric polypropylene. Copyright © 2003 John Wiley & Sons, Ltd.
Studies in Surface Science and Catalysis, 2006
The influence of the number of ancillary ligations and the corresponding structural features of t... more The influence of the number of ancillary ligations and the corresponding structural features of three titanium benzamidinate complexes 1–3, in the polymerization of propylene, has been investigated. These complexes produce similar polymers indicating the formation of similar active species. The activation process was followed via 29Si-NMR spectroscopy.
Organometallics, 2006
ABSTRACT
Organometallics, 2006
A new mechanism for the formation of stereoerrors during the polymerization of propylene, promote... more A new mechanism for the formation of stereoerrors during the polymerization of propylene, promoted by the C 2symmetric benzamidinate titanium complex 1, has been obserVed at low and high pressure using unlabeled and 2-d-labeled propylene. The use of deuterated propylene induces higher tacticities and molecular weights of the resulting polymers. At high pressure, the polymerization of the deuterated propylene induces faster insertion and termination processes. The new epimerization mechanism, which may be accompanied by a CH 2 / CD(Me) exchange, is presented.
Journal of Polymer Science Part A-polymer Chemistry, 2005
The effect of solvents (toluene, dichloromethane, and hexane) was studied on the polymerization o... more The effect of solvents (toluene, dichloromethane, and hexane) was studied on the polymerization of propylene with the octahedral complexes bis(trimethylsilyl)benzamidinate titanium dichloride(a), bis(acetylacetonate) titanium dichloride(b), and bis(diethylamino) titanium di-2-(diphenylphosphanylamino)pyridine as catalytic precursors and methylalumoxane as the cocatalyst. For comparison, the polymerization was also performed in plain liquid propylene without the addition of any solvent. The obtained polymers were fractionated by refluxing hexane. The activity of the complexes and the molecular weights and tacticities of the whole polymers and their different fractions were the studied parameters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4505–4516, 2005
Journal of The American Chemical Society, 2003
The synthesis and structural X-ray diffraction studies for some benzamidinate ligations and sever... more The synthesis and structural X-ray diffraction studies for some benzamidinate ligations and several group 4 benzamidinate complexes are presented. The use of the cis-octahedral C(2)-symmetry compounds was studied to shed light on the conceptual applicability of these complexes as potential catalysts for the stereoregular polymerization of propylene. We demonstrate that the stereoregular polymerization of propylene catalyzed by early-transition metal octahedral benzamidinate complexes, activated with either MAO or B(C(6)F(5))(3) as cocatalysts, can be modulated by pressure (from atactic to isotactic through elastomers). The different effects in the polymerization process such as the nature of solvent or cocatalyst, temperature, pressure, molar ratio catalyst:cocatalyst, and the relationship between the symmetry of the complex and the polymer microstructure have been investigated. When the complex [4-CH(3)-C(6)H(4)C(NTMS)(2)](2)ZrMe(2) (9) was activated with MAO, it was found to be a good catalyst for the polymerization of propylene, at atmospheric pressure, producing an oily polymer resembling an atactic polypropylene. Being activated with B(C(6)F(5))(3), complex 9 produces a highly isotactic (mmmm = 98%) product. Likewise, when the polymerization of propylene was performed with complex 9 and MAO at high pressure (liquid propylene), a highly stereoregular polymer was also obtained. Larger activities and stereoregularities were achieved by performing the reaction in CH(2)Cl(2) as compared to toluene. Contrary to complex 9, at atmospheric pressure the complex [4-CH(3)-C(6)H(4)C(NTMS)(2)](2)TiMe(2) (10) is not active either in CH(2)Cl(2) or in toluene. At high pressure, complex 10 produces elastomeric polypropylene. Activities of the isolobal complexes [C(6)H(4)C(NTMS)(2)](2)ZrMe(2) (11) and [C(6)H(4)C(NTMS)(2)](2)TiMe(2) (12) were found to be larger than those of complexes 9 and 10, respectively. Contrary to the structures of the elastomeric polypropylenes described in the literature, the obtained elastomers are characterized by frequent alternation of the isotactic domains with stereodefects. The stereoregular errors are formed by the intramolecular epimerization of the growing chain at the last inserted unit. The epimerization reaction was corroborated through the isomerization of alkenes.
Organometallics, 2006
The zirconium benzamidinate dimethyl complex [PhC(NSiMe 3 ) 2 ] 2 Zr(Me) 2 (1) was actiVated by a... more The zirconium benzamidinate dimethyl complex [PhC(NSiMe 3 ) 2 ] 2 Zr(Me) 2 (1) was actiVated by a mixture of trityl tetrakispentafluorophenylborate (TTPB) and a small amount of methylalumoxane (MAO) (Zr:B:Al ) 1:1:50), forming an extremely actiVe catalytic system for the polymerization of olefins, producing high-density polyethylene and elastomeric polypropylene with a narrow MWD. This catalytic system riVals the actiVity of the best nonmetallocene systems and approaches the actiVities of the best metallocene complexes. Single actiVe sites are obtained only after the addition of propylene. A plausible actiVation mechanism is proposed, which is corroborated by NMR, ESR spectroscopy, radical trapping on fullerene, and MALDI-TOF mass spectroscopy experiments.
Journal of Organometallic Chemistry, 2007
Zirconium and titanium bis(benzamidinate) dimethyl complexes were found to be active catalytic pr... more Zirconium and titanium bis(benzamidinate) dimethyl complexes were found to be active catalytic precursors for the oligomerization of mono-and bis-substituted silanes. The activation of such complexes, by an excess of MAO or by an equimolar amount of B(C 6 F 5 ) 3 , increases the catalytic activity of the complexes and the molecular weight of the obtained oligosilanes. The maximum polymerization index that was accomplished (n = 90) is by far the largest obtained with other organometallic complexes. In addition, the activated benzamidinate catalysts were also found to be active for the polymerization of 1,5-hexadiene producing poly(methyl-1,3-cyclopentane). For the latter, the results obtained with C 2 -symmetry bis(benzamidinate) dimethyl complexes were compared with a chiral complex bearing a myrtanyl group at the benzamidinate ligand.
Journal of Organometallic Chemistry, 2008
The reaction of Li2[1,2-{N(PMes2)}2C6H4], formed in situ from n-BuLi and the corresponding amines... more The reaction of Li2[1,2-{N(PMes2)}2C6H4], formed in situ from n-BuLi and the corresponding amines, with 1equiv. of [NiBr2(DME)] gives [Ni{1-N(PMes2)-2-N(μ-PMes2)C6H4-κ3N,N′,P-κ1P′}]2 (1). After activation by methylalumoxane (MAO), 1 is a highly active catalyst in the oligomerization and isomerization of α-olefins such as ethene, propene, isobutene, 1-hexene and 1,5-hexadiene. For ethene oligomerization turnover frequencies (TOFs) range from 3000 to 79015h−1, depending on the
Macromolecular Symposia, 2007
A series of dimethyl titanium benzamidinate complexes has been prepared containing various functi... more A series of dimethyl titanium benzamidinate complexes has been prepared containing various functional groups at the aromatic ring. These functional groups were selected to study their electronic or steric effects at the cationic metal center in the polymerization of propylene. Quantitative structure activity relationship (QSAR) studies showed that a linear relationship is observed only for the Taft Parameter (Es). Mono-and bis-benzamidinate complexes were found to produce similar polymers indicating that alike active species are obtained regardless of the starting complex. Deuterium labeled 2-D-propene showed that a new epimerization mechanism for this type of complexes is operative.