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Titanium Complexes (titanium + complex)
Selected AbstractsChemInform Abstract: Asymmetric Synthesis of ,-Hydroxy-,,,-acetylenic Esters Catalyzed by Oxazolidine,Titanium Complex.CHEMINFORM, Issue 3 2010Jincheng Mao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Chelating Dialkoxide Titanium Complex: A Versatile Building Block for the Construction of Heterometallic DerivativesCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2007Rosa Fandos Dr. Abstract The heterometallic complex [TiCp*(O2Bz)2AlMe2] (2) has been synthesised by reaction of [TiCp*(O2Bz)(OBzOH)] (1) with AlMe3 (Cp*=,5 -C5Me5; Bz=benzyl). Complex 1 reacts with HOTf to yield the cationic derivative [TiCp*(OBzOH)2]OTf (3) (HOTf=HSO3CF3). Compound 3 reacts with [{M(,-OH)(cod)}2] (M=Rh, Ir; cod=cyclooctadiene) to render the early,late heterometallic complexes [TiCp*(O2Bz)2{M(cod)}2]OTf (M=Rh (4); Ir (5)). The molecular structure of complex 4 has been established by single-crystal X-ray diffraction studies. [source] Enantioselective Sulfide Oxidation Catalyzed by 2,10-Camphanediol Derived Titanium Complex and Its MechanismCHINESE JOURNAL OF CHEMISTRY, Issue 8 2008Qing-Le ZENG Abstract Cumyl hydroperoxide (CHP) and tert -butyl hydroperoxide (TBHP) produced (R)- and (S)-sulfoxide in 2,10-camphanediol-titanium catalyzed sulfoxidation, respectively. During kinetic resolution, the sulfoxide configuration was reversed with CHP, but kept with TBHP. Based on these results and the ESI-MS data, the mechanism of sulfoxidation was proposed to be intramolecular nucleophilic oxygen transfer to a coordinated sulfide. [source] Monocyclopentadienyl Phenoxido,Amino and Phenoxido,Amido Titanium Complexes: Synthesis, Characterisation, and Reactivity of Asymmetric Metal Centre DerivativesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 29 2008Giuseppe Alesso Abstract Reduction of phenol,imine derivatives R,N=CH(3,5-R2C6H2 -2-OH) (R = tBu; R, = C6H51a, p -MeC6H41b, Cy 1c, tBu 1d, 2,6-Me2C6H31e; R = H; R, = p -MeC6H41f; Cy = cyclohexyl) with MBH4 (M = Li, Na) or AlLiH4 in ethyl ether or thf at room temperature affords the phenol,amine compounds R,NHCH2(3,5-R2C6H2 -2-OH) 2a,c and 2e,f. The N -R-[2,4-di- tert -butyl]benzo-1-oxa-3-azine species (R = tBu 2d1, 2,6-Me2C6H32e1) are obtained by Mannich reaction of 2,4-di- tert -butylphenol with RNH2 in refluxing methanol. Intermediate 2d1 is converted in ethanol at room temperature into N - tert -butyl[2-hydroxy-3,5-di- tert -butyl]benzylamine (2d), whereas 2e is not obtained from 2e1 by using this procedure.N -alkyl,N - tert -butyl[2-hydroxy-3,5-di- tert -butyl]benzylaminecompounds tBuN(R)CH2(3,5- tBu2C6H2 -2-OH) (R = Me 2g, Et 2h, nPr 2i, CH2Ph 2j) are also prepared by the appropriate synthetic method. Treatment of 2a,c with 1 equiv. of TiCpCl3 in the presence of 2.5 equiv. of NEt3 in hexane at room temperature gives the monocyclopentadienyl phenoxido,amido monochloride complexes TiCp[R,NCH2(3,5- tBu2C6H2 -2-O)]Cl (R, = C6H53a, R, = p -MeC6H43b, R, = Cy 3c). The analogous complex Ti(,5 -C5H4SiMe2Cl)[C6H5NCH2(3,5- tBu2C6H2 -2-O)]Cl (4a) results from the reaction of 2a with Ti(,5 -C5H4SiMe2Cl)Cl3. Nevertheless, 2d reacts with TiCpCl3 in hexane in the presence of NEt3 at room temperature yielding the monocyclopentadienyl phenoxido dichloride compound TiCp[tBuNHCH2(3,5- tBu2C6H2 -2-O)]Cl2 (5), whereas in ethyl ether and in the absence of NEt3 adduct 5·HCl is obtained, which is further converted into TiCp[tBuNCH2(3,5- tBu2C6H2 -2-O)]Cl (3d) by addition of a NEt3/ethyl ether solution. The reaction of TiCpCl3 with 2a in the presence of 2.5 equiv. of NEt3 in a polar solvent (thf, CH2Cl2 or toluene) at room temperature affords TiCp[Ph(H)NCH2(3,5- tBu2C6H2 -2-O)]Cl (6a) as a mixture of two stereoisomers. All the reported compounds were characterised by the usual analytical and spectroscopic methods and the molecular structures of 2a, 2d, 2e and 3d were determined by X-ray diffraction analysis from suitable single crystals. Preliminary studies of catalytic activity for ethylene polymerisation by using solid methylaluminoxane as cocatalyst were performed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Structure,Catalytic Activity Relationship in Bridging Silacycloalkyl Ring Conformations of Constrained Geometry Titanium ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2008Eugene Kang Abstract A series of cyclic silylene-bridged (amidocyclopentadienyl)dichlorotitanium(IV) complexes [TiCl2{,5 -1-(CySitBuN- ,N)-2,3,4,5-R4 -C5}] was prepared, where CySi = silacyclobutyl (a), silacyclopentenyl (b), silacyclopentyl (c), and silacyclohexyl (d); R = H (4), Me (5). The starting silane, dichlorosilacycloalkane CySiCl2 (1), was treated with NaCp (LiCp*), followed by LiNHtBu to yield the cyclic silylene-bridged ligands (R4C5)CySi(NHtBu) [R = H (2); Me (3)]. Subsequent deprotonation with n -butyllithium, followed by transmetalation with TiCl4 yielded the desired constrained geometry complexes (CGCs) (CpCySiNtBu)TiCl2 (4) and (Cp*CySiNtBu)TiCl2 (5). The structures of the resulting cyclopentadienyl- (4b and 4c) and tetramethylcyclopentadienyl(silacycloalkyl)amidotitanium(IV) dichloride (5a, 5c, and 5d) species were studied by using X-ray crystallography to obtain geometrical information on cyclic silylene-modified CGCs. The ethylene polymerization by the cyclic silylene-bridged CGCs 4 and 5 was examined to verify the structure,catalytic activity relationship derived from variation of the size of a cyclic silylene ring. Indeed, the size of the cyclic silylene ring at the 1,1,-position of 4 and 5 affected the catalytic activities through the ethylene polymerization. Systematic increase in the catalytic activities was observed as the cyclic silylene-bridging unit was expanded from a four- to six-membered ring. In the present study, we found that CGCs of TiIV with a six-membered silylene-bridged ligand (5d) produced active catalytic species for the formation of polyethylene with Mw = 42.7,×,10,4 g,mol,1 and Mw/Mn = 2.1 with excellent catalytic activities (20.9 kg,polymer per mmol of Ti). When titanium(IV) dimethyl complex (6d) was applied in continuous polymerization process, impressive high catalytic activity on copolymerization with 1-octene was observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Facile Formation of Hexacyclic [Al3O2Cl] Aluminum and Alkoxide-Bridged Titanium Complexes: Reactions of AlMe3 with [Ti(L)Cl2] [L = 2,2,-Methylenebis(6- tert -butyl-4-methylphenolato)]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2007Dao Zhang Abstract The titanium dichloride complex [(L)TiCl2] [L = 2,2,-methylenebis(6- tert- butyl-4-methylphenolato)] (1) reacted with trimethylaluminum (AlMe3) in a 1:2 ratio to give a trimetallic aluminum complex of the composition [(L)(AlMe2)3(,-Cl)] (2) with a symmetric six-membered ring [Al3(,2 -O)2(,2 -Cl)] and a four-coordinate aluminum center in the solid state. The reaction of 1 equiv. AlMe3 gave [(L)TiMeCl] (3), which could absorb O2 gas to afford the oxygen-insertion product [{(L)TiCl}2(,-OMe)2] (4) with a five-coordinate metal center. Upon reaction of H2L with AlMe3, the binuclear, four-coordinate adduct [{(L)AlMe}2] (5) was formed. Complex 4 supported on MgCl2 and activated with aluminum alkyls reveals high catalytic activity for ethylene polymerization to produce polymers with molecular weight distributions of ca. 3.1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] ChemInform Abstract: New Chiral Titanium Complexes for Enantioselective Reductive Cyclizations of Diimines to trans-2,3-Diarylpiperazines.CHEMINFORM, Issue 24 2008Pothiappan Vairaprakash Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Ligand-Bridged and Bis-Ligand-Coordinated Titanium Complexes: Synthesis, Structure and Relevance to Phenylacetylene Hydroanilination Catalysis.CHEMINFORM, Issue 5 2008Xiao-Yu Han Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Hydroamination/Hydrosilylation Sequence Catalyzed by Titanium Complexes.CHEMINFORM, Issue 4 2006Andreas Heutling Abstract For Abstract see ChemInform Abstract in Full Text. [source] Stereofacial Control in Asymmetric Cyanosilylation of Aldehydes Catalyzed by Novel S-Proline-Derived Titanium Complexes.CHEMINFORM, Issue 1 2006Yun Bong Kim Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Asymmetric Trialkylaluminum Addition to Aldehydes Catalyzed by Titanium Complexes of N-Sulfonylated Amino Alcohols with Two Stereogenic Centers.CHEMINFORM, Issue 52 2001Jing-Song You Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Titanium complexes with sulfur-linked bis(phenolate) ligandsACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2009Thomas S. Dols High-quality crystals of two bis(phenolate)titanium complexes, namely dichlorido{4,4,-dimethyl-2,2,-[cyclohexane-1,2-diylbis(sulfanediyl)]diphenolato}titanium(IV), [Ti(C20H22O2S2)Cl2], (I), and dichlorido{2,2,-[cyclohexane-1,2-diylbis(sulfanediyl)]diphenolato}titanium(IV), [Ti(C18H18O2S2)Cl2], (II), were obtained by reactive crystallization. Depending on the solvent, compound (II) was obtained as unsolvated (IIa) or as the toluene hemisolvate, [Ti(C18H18O2S2)Cl2]·0.5C7H8, (IIb). These systems without bulky substituents on the aromatic phenolate rings serve as ideal model compounds for precatalysts. The excellent X-ray diffraction data will help clarify the nature of the mismatched interactions between the soft S atoms within the ligand and the hard titanium center. Molecule (I) has crystallographic C2 symmetry. [source] Studies of the Nature of the Catalytic Species in the ,-Olefin Polymerisation Processes Generated by the Reaction of Diamido(cyclopentadienyl)titanium Complexes with Aluminium Reagents as CocatalystsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2005Vanessa Tabernero Abstract The reaction of the diamido(chloro)cyclopentadienyltitanium compounds TiCpRx[1,2-C6H4(NR,)2]Cl [CpRx = ,5 -C5H5, ,5 -C5(CH3)5, ,5 -C5H4(SiMe3); R, = CH2tBu, Pr] with the Grignard reagent MgClR (R = Me, CH2Ph) affords the monomethyl and monobenzyl derivatives TiCpRx[1,2-C6H4(NR,)2]R. Upon addition of methylaluminoxane (MAO), the chloro- and alkyltitanium complexes show low activity towards the polymerisation of ethylene and styrene. However, no methylation was observed during the treatment of trimethylaluminium with the chloro compounds TiCpRx[1,2-C6H4(NR,)2]Cl. Instead, these reactions give the dinuclear aluminium complexes Al2[1,2-C6H4(NR,)2]Me4 (R, = CH2tBu, Pr) through transmetallation of the diamido ligand, suggesting a deactivation process of the catalysts in the olefin polymerisation reactions. In an additional effort to model the catalytic species, stoichiometric reactions between the methyl derivatives TiCpRx[1,2-C6H4(NR,)2]Me and solid methylaluminoxane (MAO) were studied by NMR spectroscopy. Monitoring of these reactions revealed the formation of zwitterionic species depending on the nature of the solvent. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Bis(oxazoline)titanium Complexes as Chiral Catalysts for Enantioselective Hydrosilylation of Ketones , A Combined Experimental and Theoretical Investigation.CHEMINFORM, Issue 47 2003Marco Bandini Abstract For Abstract see ChemInform Abstract in Full Text. [source] Asymmetric Synthesis of anti-Homopropargylic Alcohols from Aldehydes and Chiral Sulfonimidoyl Substituted Bis(allyl)titanium Complexes Through Generation and Elimination of Novel Chiral Alkylidenecarbene (Dimethylamino)sulfoxonium Ylides.CHEMINFORM, Issue 2 2003Leleti Rajender Reddy Abstract For Abstract see ChemInform Abstract in Full Text. [source] Titanium dioxide nanoparticles-coated column for capillary electrochromatographic separation of oligopeptidesELECTROPHORESIS, Issue 21 2005Yi-Ling Hsieh Abstract A novel column made through the condensation reaction of TiO2 nanoparticles (TiO2,NPs) with silanol groups of the fused-silica capillary is described. EOF measurements under various buffer constitutions were used to monitor the completion of reactions. The results indicated that the EOF was dependent on the interactions between buffers and the bonded TiO2,NPs. With formate/Tris buffer, EOF reversal at pH below,5 and cathodic EOF at pH above,5 were indicated. The pI of the bonded TiO2,NPs was found at ,ph,5. Only cathodic EOF was illustrated by substituting the mobile phase with either glutamate or phosphate buffer. It was elucidated that both glutamate and phosphate buffer yield a negative charge layer on the surface of TiO2,NPs attributable to the formation of a titanium complex. The CEC performance of the column was tested with angiotensin-type oligopeptides. Some parameters that would affect the retention behavior were investigated. The interactions between the bonded phases and the analytes were explicated by epitomized acid,base functional groups of the oligopepetides and the speciation of the surface oxide in different pH ranges. The average separation efficiencies of 3.1×104,plates/m is readily achieved with a column of 70,cm (50,cm)×50,,m,ID under an applied voltage of 15,kV, phosphate buffer (pH,6.0, 40,mM), and UV detection at 214,nm. [source] Dinuclear Titanium(IV) Complexes Bearing Phenoxide-Tethered N-Heterocyclic Carbene Ligands with cisoid Conformation through Control of HydrolysisEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 30 2007Dao Zhang Abstract In situ generated N-heterocyclic carbene salt derivative Na2(L) of 1,3-bis(4,6-di- tert -butyl-2-hydroxybenzyl)imidazolium bromide, [H3(L)]Br, reacted with 1 equiv. of TiBr4 at ,78 °C to give a titanium complex of the composition [(L)TiBr2(thf)] (1), while the reaction in a 2:1 ratio under the same conditions afforded bisligand titanium complex [(L)2Ti] (2). Two oxygen-bridged titanium dimers, {[(L)TiBr]2(,-O)} (4) and {[(L)Ti(,-O)]2} (5), were obtained by control of hydrolysis of 1 and [(L)Ti(CH2Ph)2] (3) in tetrahydrofuran and diethyl ether. The molecular structures of 2, 4, and 5 have been confirmed by X-ray single-crystal analysis. The phenoxide-functionalized NHC ligand adopts transoid conformation in mononuclear complex 2 but rare cisoid conformation in dinuclear complexes 4 and 5. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Enantioselective Cyanosilylation of Ketones Catalyzed by a Nitrogen-Containing Bifunctional CatalystADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2006Yan Xiong Abstract An efficient and optically active, bifunctional tetraaza ligand (2S)- N -{(1R,2R)-2-[(S)-pyrrolidine-2-carboxamido]-1,2-diphenylethyl}pyrrolidine-2-carboxamide has been developed for the addition of trimethylsilyl cyanide (TMSCN) to ketones. The bifunctional catalyst system based on a monometallic titanium complex was found to be a highly enantioselective catalyst to provide O -TMS cyanohydrins with up to 94% ee. A possible transition state has been proposed to explain the origin of the activation and asymmetric inductivity. [source] Copolymerization of ethylene with styrene catalyzed by a linked bis(phenolato) titanium catalystJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2006Carmine Capacchione Abstract Copolymerization of ethylene with styrene, catalyzed by 1,4-dithiabutanediyl-linked bis(phenolato) titanium complex and methylaluminoxane, produced exclusively ethylene,styrene copolymers with high activity. Copolymerization parameters were calculated to be rE = 1.2 for ethylene and rS = 0.031 for styrene, with rErS = 0.037 indicating preference for alternating copolymerization. The copolymer microstructure can be varied by changing the ratio between the monomers in the copolymerization feed, affording copolymers with styrene content up to 68%. The copolymer microstructure was fully elucidated by 13C NMR spectroscopy revealing, in the copolymers with styrene content higher than 50%, the presence of long styrene,styrene homosequences, occasionally interrupted by isolated ethylene units. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1908,1913, 2006 [source] Synthesis of ,-conjugated polymers via regioregular organometallic polymers 2.APPLIED ORGANOMETALLIC CHEMISTRY, Issue 8 2010Transformation of titanacyclopentadiene- containing polymer into poly(p -phenylene) derivative Abstract The transformation of a regioregular organometallic polymer possessing titanacyclopentadiene-2,5-diyl units into a poly(p -phenylene) derivative by means of a novel polymer reaction method is described. The organotitianium polymer was prepared by the polymerization of 1,4-diethynyl-2,5-dioctyloxybenzene and a low-valent titanium complex, generated in situ from titanium(IV) isopropoxide and isopropylmagnesium chloride, and was subjected to the reaction with 3-bromo-1-propyne followed by the protonation. Consequently, a polymer consisting of the substituted phenylene-1,4-diyl units could be produced in a high yield, which is soluble in organic solvents such as chloroform. The number-average molecular weight and the molecular weight distribution of the polymer were estimated as 4800 and 1.8, respectively (GPC, polystyrene). The UV,vis absorption spectrum of the polymer exhibited the absorption maximum (,max) at 329 nm, which was bathochromically shifted by 53 nm compared with that of a model compound, 1,4-bis(2-methoxyphenyl)-2-methylbenzene (,max = 276 nm). Copyright © 2010 John Wiley & Sons, Ltd. [source] Synthesis of a new salphen-type titanium complex and its application in ethylene polymerization and copolymerizationAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2010Xiaojing Wen Abstract TiCl2[salphen(di- tBu)] was synthesized, characterized and employed as pre-catalyst in ethylene homo- and copolymerization with propylene, 1-octene and 10-undecen-1-ol. X-ray diffraction study on the titanium complex revealed a distorted octahedral coordination of the central metal with a trans -Cl, cis -O, cis -N arrangement. The complex combined with MAO afforded moderate catalytic activities in ethylene polymerization. Furthermore the catalyst not only copolymerized ethylene with apolar monomer (propylene and 1-octene), but also possessed significant capability of incorporation with polar monomer (10-undecen-1-ol). Only single insertion of 1-octene unit in ethylene- co -1-octene polymer was detected by 13C NMR spectrum. Copyright © 2010 John Wiley & Sons, Ltd. [source] Bis-Chelated Imine-Alkoxytitanium Complexes: Novel Chiral Dopants with High Helical Twisting Power in Liquid CrystalsCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2005Manfred Braun Prof. Dr. Abstract Enantiomerically and diastereomerically pure bis-chelated imine-alkoxytitanium complexes 6 and 7 have been synthesized and used as chiral dopants for converting nematic into cholesteric phases. The dopants were tested in mainly commercially available nematic liquid crystalline compounds or mixtures: LC1 (BASF), ZLI-1695 and ZLI-1840 (Merck), as well as N -(4-methoxybenzylidene)-4,-butylaniline (MBBA). The values of the helical twisting power (HTP) were determined by the Grandjean,Cano method. Exceptionally high helical twisting powers were obtained. Thus, the titanium complex 6,h displayed a HTP value of 740 ,m,1 in MBBA, the highest HTP value reported. The helical twisting power has been found to depend strongly on the structure of the nematic phase and the substitution pattern of the chiral ligand in the titanium complexes 6 and 7. Crystal structure analysis of 6,f confirmed the A,R,R configuration of the metal complex. The chiral imine ligands 4 and 5 were derived from the regioisomeric amino alcohols 1 and 2. [source] Novel, Sensitive Voltammetric Methods for Titanium Determination Using Chromotropic Acid and Azo-Compounds as Complexing AgentsELECTROANALYSIS, Issue 12 2003Marcin Gawrys Abstract Voltammetric behavior of titanium(IV) complexes with chromotropic acid, its azo-derivatives: 2-(4-sulfophenylazo)-1,8-dihydroxy-3,6-naphthalenedisulfonic acid (SPANDS), chromotrope 2B, sulfonazo III and other azo-compounds: calmagite, tropeoline O and kalces was investigated at a hanging mercury drop electrode. These complexes strongly adsorb onto the electrode, thus can be determined by an adsorptive stripping voltammetry (optimal pH about 6). At pH about 3 reduction current enhancement for Ti-kalces complex was observed in the presence of chlorate ions. It is a rare example of a catalytic process with azo-compound as a complexing agent. Signal for Fe-calmagite complex reduction was also observed. Influence of foreign ions and the optimal conditions for titanium determination are described in detail. Additionally, a connection between obtained results and a structure of titanium complexes is discussed. [source] Bulky-Hindrance-Controlled Ligand Transformation from Linked Bis(amidinate) to Linked Imido-Amidinate Promoted by a Mono(cyclopentadienyl)titanium GroupEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2006Sheng-Di Bai Abstract A novel class of silyl-linked bis(amidinate) ligands [SiMe2{NC(Ph)N(2,6-R2Ph)Li}2] [L1 (R = H), L2 (R = Me), and L3 (R = iPr)] reacted with TiCl3(C5H5) to produce the half-sandwich titanium complexes 1, 2, and 3. The molecular structures of 1,3 were confirmed successfully by X-ray crystallography. An unprecedented intramolecular ligand transformation from the linked bis(amidinate) configuration to the linked imido-amidinate configuration took place in the cases of L1 and L2. It was found that the rearrangement process was related to the steric hindrance of the terminal substituents. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Bis(salicylaldiminato)titanium Complexes Containing Bulky Imine Substituents: Synthesis, Characterization and Ethene Polymerization StudiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2005Antti Pärssinen Abstract A series of titanium complexes bearing two anionic [N, O,] bidentate salicylaldiminato ligands, namely bis[(N -salicylidene)anilinato]titanium(IV) dichloride (1), bis[(N -salicylidene)-2,6-dimethylanilinato]titanium(IV) dichloride (2), bis[(N -salicylidene)-2,6-di- i - propylanilinato]titanium(IV) dichloride (3), bis[(N -salicylidene)-(1-naphthalenylimino)]titanium(IV) dichloride (4), bis[(N -salicylidene)-2,6-difluoroanilinato]titanium(IV) dichloride (5), and bis[(N -3-fluorosalicylidene)-2,6-difluoroanilinato]titanium(IV) dichloride (6) have been synthesized with good yields by a two-step procedure. The X-ray structure analysis reveals that in complex 2, titanium has a distorted octahedral coordination sphere in which the oxygen atoms and the chloride ligands form the basal plane. Both the chloride and the phenoxy moieties have a cis orientation and the angle between the chloride ligands is 93.05°. The imine nitrogen atoms complete the octahedral coordination of the Ti center by occupying the axial positions. The newly synthesized (2 and 4,6) and already known complexes (1 and 3) were introduced in detailed ethene-polymerization studies. The activities achieved were low to moderate depending on the size and nature of the imino substituents. The polyethenes (PEs) produced had high molar masses, and the modalities of the molecular weight distributions varyied with polymerization temperature. Based on the results of ab initio calculations and on the experimental data obtained, an explanation for uni- and bimodal polymerization behavior and the differences in catalytic activities are given. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Computational study of titanium (IV) complexes with organic chromophoresINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2006Ivan Kondov Abstract A computational study of small titanium complexes with the chromophores catechol, alizarin, and coumarin 343 is presented. Employing density functional theory (DFT), the ground-state geometries, energies, and harmonic frequencies of the different compounds are calculated. Furthermore, time-dependent DFT and the configuration interaction singles (CIS) method are used to determine excitation energies and excited-state gradients. Based on these results, the character of the excited states as well as electronic-vibrational coupling strengths are analyzed, and the implications for electron-transfer reactions at dye,semiconductor interfaces are discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Facile, Efficient Copolymerization of Ethylene with Bicyclic, Non-Conjugated Dienes by Titanium Complexes Bearing Bis(,-Enaminoketonato) LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Jing-yu Liu Abstract Copolymerizations of ethylene with 5-vinyl-2-norbornene or 5-ethylidene-2-norbornene under the action of various titanium complexes bearing bis(,-enaminoketonato) chelate ligands of the type, [R1NC(R2)CHC(R3)O]2TiCl2 (1, R1=Ph, R2=CF3, R3=Ph; 2, R1=C6H4F- p, R2=CF3, R3=Ph; 3, R1=Ph, R2=CF3, R3=t- Bu; 4, R1=C6H4F- p, R2=CF3, R3=t- Bu; 5, R1=Ph, R2=CH3, R3=CF3; 6, R1=C6H4F- p, R2=CH3, R3=CF3), have been shown to occur with the regioselective insertion of the endocyclic double bond of the monomer into the copolymer chain, leaving the exocyclic vinyl double bond as a pendant unsaturation. The ligand modification strongly affects the copolymerization behaviour. High catalytic activities and efficient co-monomer incorporation can be easily obtained by optimizing the catalyst structures and polymerization conditions. [source] Titanium-mediated [CpTiCl2(OEt)] ring-opening polymerization of lactides: A novel route to well-defined polylactide-based complex macromolecular architecturesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2010Nikolaos Petzetakis Abstract Among three cyclopentadienyl titanium complexes studied, CpTiCl2(OEt), containing a 5% excess CpTiCl3, has proven to be a very efficient catalyst for the ring-opening polymerization (ROP) of L -lactide (LLA) in toluene at 130 °C. Kinetic studies revealed that the polymerization yield (up to 100%) and the molecular weight increase linearly with time, leading to well-defined PLLA with narrow molecular weight distributions (Mw/Mn , 1.1). Based on the above results, PS- b -PLLA, PI- b -PLLA, PEO- b -PLLA block copolymers, and a PS- b -PI- b -PLLA triblock terpolymer were synthesized. The synthetic strategy involved: (a) the preparation of OH-end-functionalized homopolymers or diblock copolymers by anionic polymerization, (b) the reaction of the OH-functionalized polymers with CpTiCl3 to give the corresponding Ti-macrocatalyst, and (c) the ROP of LLA to afford the final block copolymers. PMMA- g -PLLA [PMMA: poly(methyl methacrylate)] was also synthesized by: (a) the reaction of CpTiCl3 with 2-hydroxy ethyl methacrylate, HEMA, to give the Ti-HEMA-catalyst, (b) the ROP of LLA to afford a PLLA methacrylic-macromonomer, and (c) the copolymerization (conventional and ATRP) of the macromonomer with MMA to afford the final graft copolymer. Intermediate and final products were characterized by NMR spectroscopy and size exclusion chromatography, equipped with refractive index and two-angle laser light scattering detectors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1092,1103, 2010 [source] Homo- and copolymerization of ethylene and norbornene with bis(,-diketiminato) titanium complexes activated with methylaluminoxaneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2008Yongfei Li Abstract Homo- and copolymerization of ethylene and norbornene were investigated with bis(,-diketiminato) titanium complexes [ArNC(CR3)CHC(CR3)NAr]2TiCl2 (R = F, Ar = 2,6-diisopropylphenyl 2a; R = F, Ar = 2,6-dimethylphenyl 2b; R = H, Ar = 2,6-diisopropylphenyl 2c; R = H, Ar = 2,6-dimethylphenyl 2d) in the presence of methylaluminoxane (MAO). The influence of steric and electric effects of complexes on catalytic activity was evaluated. With MAO as cocatalyst, complexes 2a,d are moderately active catalysts for ethylene polymerization producing high-molecular weight polyethylenes bearing linear structures, but low active catalysts for norbornene polymerization. Moreover, 2a,d are also active ethylene,norbornene (E,N) copolymerization catalysts. The incorporation of norbornene in the E,N copolymer could be controlled by varying the charged norbornene. 13C NMR analyses showed the microstructures of the E,N copolymers were predominantly alternated and isolated norbornene units in copolymer, dyad, and triad sequences of norbornene were detected in the E,N copolymers with high incorporated content of norbornene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 93,101, 2008 [source] Ethylene/,-olefin copolymerization with bis(,-enaminoketonato) titanium complexes activated with modified methylaluminoxaneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2005Li-Ming Tang Abstract Copolymerizations of ethylene with ,-olefins (i.e., 1-hexene, 1-octene, allylbenzene, and 4-phenyl-1-butene) using the bis(,-enaminoketonato) titanium complexes [(Ph)NC(R2)CHC(R1)O]2TiCl2 (1a: R1 = CF3, R2 = CH3; 1b: R1 = Ph, R2 = CF3; and 1c: R1 = t -Bu, R2 = CF3), activated with modified methylaluminoxane as a cocatalyst, have been investigated. The catalyst activity, comonomer incorporation, and molecular weight, and molecular weight distribution of the polymers produced can be controlled over a wide range by the variation of the catalyst structure, ,-olefin, and reaction parameters such as the comonomer feed concentration. The substituents R1 and R2 of the ligands affect considerably both the catalyst activity and comonomer incorporation. Precatalyst 1a exhibits high catalytic activity and produces high-molecular-weight copolymers with high ,-olefin insertion. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6323,6330, 2005 [source] |