Binuclear Titanium Complexes Research Articles

Significant cooperative effects in binuclear titanium complexes based on trifluoromethyl substituted bis-β-carbonylenamine ligands for ethylene (co)polymerization

The binuclear cooperative effect could greatly improve the catalytic performances for olefin polymerization but has rarely been utilized in early transition nonmetallocene binuclear complexes. Here a series of m- and p-phenylene-bridged bis-β-carbonylenamine ligands and the corresponding binuclear titanium complexes (Ti2mLa-Ti2mLc, Ti2pLa) were synthesized and characterized, with the molecular structure of ligand mLa further characterized by single crystal X-ray diffraction, which indicated that methylthio aniline reacted with the carbonyl next to trifluoromethyl group, thus led to relatively short metal-metal separation in binuclear complexes. Activated by MAO, the binuclear complex Ti2mLa exhibited the highest activity for ethylene polymerization and ethylene/α-olefins copolymerization, and the highest comonomer incorporation, relative to other binuclear Ti2mLb, Ti2mLc and Ti2pLa and mononuclear Ti1La. For ethylene polymerization, the activity of complex Ti2mLa was almost 4 and 2.6 times those of p-phenylene-bridged derivative Ti2pLa and mononuclear Ti1La, and the activity of complex Ti2mLa for ethylene/1-hexene copolymerization was 2 and 4.8 times those of Ti2pLa and Ti1La. Furthermore, the incorporation of comonomer for ethylene/1-hexene copolymerization produced by Ti2mLa was more than twice that of Ti2pLa and triple that of Ti1La. All these results clearly showed that stronger bimetallic cooperative effect existed in binuclear titanium complex Ti2mLa due to shorter metal-metal distance.

Phenyl-bridged bis-salicylaldiminato binuclear titanium complexes for ethylene (co)polymerization

Phenyl-bridged bis-salicylaldiminato binuclear titanium complexes for ethylene (co)polymerization

Fixation of Dinitrogen at an Asymmetric Binuclear Titanium Complex.

A new type of dititanium dinitrogen complex supported by a triphenolamine (TPA) ligand is reported. Analysis by single-crystal X-ray diffraction and Raman and NMR spectroscopy reveals different coordination geometries for the two titanium centers. Hence, coordination of TPA and a nitrogen ligand results in trigonal-bipyramidal geometry, while an octahedral titanium center is obtained upon additional coordination of an ethoxide generated upon C-O bond cleavage in a diethyl ether solvent molecule. The titanium complex successfully generates ammonia in the presence of an excess amount of PCy3HI and KC8 in 154% yield (per titanium atom). A titanium complex with a bulkier TPA does not form a dinitrogen complex, and mononuclear titanium dinitrogen complexes were not accessible, presumably because of the high tendency of early transition metals to form binuclear dinitrogen complexes.

Asymmetric bis-salicylaldiminato binuclear titanium complexes for ethylene polymerization and copolymerization

Asymmetric binuclear Ti complexes were synthesized, which exhibited excellent activity for ethylene homopolymerization and copolymerization with 1-hexene or norbornene and high comonomer insertion efficiency under MMAO activation.

Synthesis, characterization, DNA-binding and biological studies of novel titanium (IV) complexes

A series of novel binuclear titanium (IV) complexes, [Ti(sal)LI–V(OBu)(μ-OBu)]2, was synthesized by the reaction of salicylic acid (H2sal) and substituted indoles (LI = Tryptophol, LII = 5-Methoxyindole, LIII = Indole-5-Carboxaldehyde, LIV = 5-Cyanoindole, LV = 6-Nitroindole) with titanium(IV) tetrabutoxide in predetermined molar ratios under stirring and refluxing conditions in THF solvent. The chemical structure of synthesized complexes was found to be binuclear based on the FTIR, IH (proton) NMR and ESI-Mass (Electron-spray ionization) spectroscopic data. Each titanium metal was surrounded by two bridged butoxy groups and one terminal butoxy group along with bidentate salicylic acid and coordinated substituted indoles. These complexes were investigated for antioxidant potential using DPPH (2,2-diphenyl-1-picrylhydrazyl) assay where they exhibited moderate to good antioxidant activity. Gel electrophoresis method was employed to study the ct-DNA (calf thymus DNA) cleavage efficiency of complexes using an agarose gel. Antimicrobial results stated that most of the complexes were ineffective against selected bacterial and fungal strains. Complexes were investigated for anticancer activity against two selected cancerous cell lines (L6 and L929). From MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay, it has been inferred that complexes 1 and 2 have better anticancer properties than their respective indoles. The DNA binding study of synthesized complexes studied in order to check their efficacy to hinder DNA replication/transcription using electronic absorption and fluorescence spectroscopy revealed them as electrostatic/groove binder. The synthesized complexes were also evaluated for antidiabetic properties using alpha-amylase inhibition assay and complex 5 possessed better alpha-amylase inhibition activity than other complexes. Synopsis: The synthesis, structural characterizationand biological activities of a novel binuclear titanium(IV) complexes [Ti(sal)LI–V(OBu)(μ-OBu)]2 is reported.

Binuclear titanium complexes coordinated by rigid p‐phenylene linked bis‐β‐carbonylenamine: Synthesis, structure, ethylene polymerization and copolymerization with 1,5‐hexadiene

Binuclear complexes for olefin polymerization have attracted great attention due to their unique catalytic properties compared with their mononuclear counterparts. Here a series of p‐phenylene‐bridgedbis‐β‐carbonylenamine ligands and their binuclear Ti complexes Ti2L1–Ti2L3 were prepared and characterized by 1H NMR, 13C NMR, Fourier transform infrared spectroscopy, and elemental analysis. The binuclear complex Ti2L3 bearing an octylthio sidearm was further investigated by single‐crystalX‐ray diffraction, which revealed that the ligand was of β‐imino enol form, with one titanium atom ligated with six other atoms, forming a deformed octahedral configuration. Furthermore, the ligand in Ti2L3 adopted a cis configuration, which was different from the trans configuration of its m‐phenylene‐bridged derivatives. These binuclear complexes (Ti2L1–Ti2L3) could catalyze ethylene polymerization and copolymerization with 1,5‐hexadiene(1,5‐HD) efficiently under modified methylaluminoxane activation. Compared with the mononuclear complex TiL5, the binuclear catalysts were thermally more stable and showed higher activity for ethylene polymerization at higher temperatures. The activity of these titanium complexes for the copolymerization of ethylene with 1,5‐HD were over 106 g/mol Ti.h.atm, almost twice as high as for homopolymerization. Compared with the mononuclear analogue TiL5 and the m‐substituted binuclear derivative Ti2L4, binuclear catalyst Ti2L2 showed higher activity and insertion rate of the comonomer. The activity of Ti2L2 was two to three times higher than that of TiL5 and Ti2L4, indicating that p‐substituted binuclear catalysts generate clear bimetallic synergistic effect for the copolymerization of ethylene and 1,5‐HD. Meanwhile, 1,5‐HD takes 1,3‐cyclopentyl form in the polymer by 1,3‐insertion. The copolymer prepared by binuclear catalysts had higher molecular weight and wider molecular weight distribution than that prepared by the mononuclear catalyst.

Chiral Discrimination of Varied Ammonium Compounds through 1H NMR Using a Binuclear Ti Complex Sensor.

A simple chiral binuclear titanium complex ((S)-Ti2L3Na4) was first prepared and served as an excellent chiral sensor for discriminating a variety of chiral ammoniums by 1H NMR. In the presence of trifluoroacetic acid, the in-situ-generated ammoniums of varied amines can be effectively resolved by (S)-Ti2L3Na4. The different binding forces between (S)-Ti2L3Na4 and two enantiomers of analytes generate different shielding effects on two enantiomers, resulting in a split in the distinguishable chemical shift.

Methylene-Bridged Tridentate Salicylaldiminato Binuclear Titanium Complexes as Copolymerization Catalysts for the Preparation of LLDPE through [Fe]/[Ti] Tandem Catalysis.

A novel tandem catalysis system consisted of salicylaldiminato binuclear/mononuclear titanium and 2,6-bis(imino)pyridyl iron complexes was developed to catalyze ethylene in-situ copolymerization. Linear low-density polyethylene (LLDPE) with varying molecular weight and branching degree was successfully prepared with ethylene as the sole monomer feed. The polymerization conditions, including the reaction temperature, the Fi/Ti molar ratio, and the structures of bi- or mononuclear Ti complexes were found to greatly influence the catalytic performances and the properties of obtained polymers. The polymers were characterized by differential scanning calorimetry (DSC), high temperature gel permeation chromatography (GPC) and high temperature 13C NMR spectroscopy, and found to contain ethyl, butyl, as well as some longer branches. The binuclear titanium complexes demonstrated excellent catalytic activity (up to 8.95 × 106 g/molTi·h·atm) and showed a strong positive comonomer effect when combined with the bisiminopyridyl Fe complex. The branching degree can be tuned from 2.53 to 22.89/1000C by changing the reaction conditions or using different copolymerization pre-catalysts. The melting points, crystallinity and molecular weights of the products can also be modified accordingly. The binuclear complex Ti2L1 with methylthio sidearm showed higher capability for comonomer incorporation and produced polymers with higher branching degree and much higher molecular weight compared with the mononuclear analogue.

Enantioselective Epoxidation of β,γ-Unsaturated Carboxylic Acids by a Cooperative Binuclear Titanium Complex

Enantioselective epoxidation of β,γ-unsaturated carboxylic acids with a cooperative binuclear titanium complex has been developed to provide single diastereomer γ-lactones in high yields and enantioselectivities via intramolecular cyclization. For the success of the reaction, the proper distance between the carboxylic acid and alkene is quite important, offering the regioselective epoxidation of unsaturated carboxylic acids bearing two similar alkenes.

Binuclear and Hexanuclear Ti(IV) Complexes Supported by [OOOO]4–-type Ligand for Preparing Disentangled UHMWPE

Binuclear and hexanuclear titanium complexes stabilized by tetradentate [OOOO]4–-type ligand were active in ethylene polymerization in the presence of Et2AlCl/Bu2Mg binary co-catalyst, giving high molecular weight polyethylene. The binuclear complex showed significantly higher catalytic activity and thermal stability in comparison to mononuclear analogue. Ultra high molecular weight polyethylene (UHMWPE) samples were processed by a solid-state uniaxial deformation into high-strength (up to 2.5 GPa) and highmodulus (over 100 GPa) oriented film tapes, which indirectly indicates a low degree of entanglements between the macromolecular chains.

A Methylene-bridged salicylaldiminato tridentate [ONS] binuclear titanium complex for ethylene-norbornene copolymerization

ABSTRACTA binuclear titanium complex Ti2La with methylene-bridged salicylaldiminato tridentate [ONS] ligand bearing octylthio sidearm was synthesized and used for the copolymerization of ethylene and norbornene (E-NB). The complex exhibited activity over 106 g/mol(Ti).h.atm and high degree incorporation of co-monomer (up to 49.9 mol %), affording high-molecular-weight copolymers with narrow molecular weight distribution. The E-NB copolymers produced by Ti2La/MMAO contained NN dyad and NNN triad sequences even at low norbornene feeds, in contrast to the observation of such sequences only at high level of NB incorporation for most other catalyst systems. The monomer reactivity ratios were calculated to be rE = 14.62 and rN = 0.08, of which the rN value was much larger than that from non-metallocene titanium catalyst systems. The catalytic performances of the binuclear complex Ti2La and its mononuclear analogue TiLb were also compared, with the binuclear complex exhibiting higher catalytic activity and NB incorporation ratio due to the binuclear cooperative effect, and producing much higher molecular weight copolymer due to the increased steric hindrance caused by close proximity of two growing chains. To the best of our knowledge, this is one of the few examples of binuclear catalyst for E-NB copolymerization with high activity and efficient incorporation of norbornene.

Synthesis, characterization and olefin polymerization behaviors of phenylene-bridged bis-β-carbonylenamine binuclear titanium complexes

Binuclear and multinuclear complexes have attracted much attention due to their unique catalytic performances for olefin polymerization compared with their mononuclear counterparts. In this work, a series of phenyl-bridged bis-β-carbonylenamine [O−NSR] (R = alkyl or phenyl) tridentate ligands and their binuclear titanium complexes (Ti2L1–Ti2L5) were synthesized and characterized by 1H NMR, 13C NMR, FTIR and elemental analysis. The molecular structure of ligand L2 (R = nPr) and its corresponding Ti complex Ti2L2 were further investigated by single-crystal X-ray diffraction, which showed that each titanium coordinated with six atoms to form a distorted octahedral configuration along with the conversion of the ligand from β-carbonylenamine to β-imino enol form. Under the activation of MMAO, these complexes catalyzed ethylene polymerization and ethylene/α-olefin copolymerization with extremely high activity (over 106 g mol (Ti)−1 h−1 atm−1) to produce high molecular weight polyethylene. At the same time, wider polydispersity as compared with the mononuclear counterpart TiL6 was observed, indicating that two active catalytic centers may be present, consistent with the asymmetrical crystal structure of the binuclear titanium complex. Furthermore, these complexes possessed better thermal stability than their mononuclear analogues. Compared with the complexes bearing alkylthio sidearms, the complex Ti2L5 bearing a phenylthio sidearm exhibited higher catalytic activity towards ethylene polymerization and produced polyethylene with much higher molecular weight, but with an appreciably lower 1-hexene incorporation ratio. Nevertheless, these bis-β-carbonylenamine-derived binuclear titanium complexes showed much higher ethylene/1-hexene copolymerization activity and 1-hexene incorporation ratios as compared with the methylene-bridged bis-salicylaldiminato binuclear titanium complexes, and the molecular weight and 1-hexene incorporation ratio could be flexibly tuned by the initial feed of α-olefin commoners and catalyst structures.

A novel tridentate [ONS] binuclear titanium complex bearing oxo-bridged macrocyclic structure for ethylene polymerization

A novel xanthene-bridged bissalicylaldiminato tridentate [ONS] ligand ligated binuclear titanium complex Ti2L bearing oxo-bridged macrocyclic structure were synthesized and characterized by 1H NMR, IR and elemental analysis. This binuclear complex Ti2L was also investigated by single-crystal X-ray diffraction, which demonstrated C2 symmetric structure with each titanium coordinated with six atoms and formed a distorted octahedral configuration. The two titanium centers were also bridged by an oxygen atom to form a relatively stable macrocyclic structure. The binuclear complex exhibited excellent activity up to 1.99 × 106 g/molTi·h for ethylene polymerization upon activation with modified methylaluminoxane (MMAO), producing high molecular weight polyethylene with bimodal distribution. The reaction conditions, such as ethylene pressure, Al/Ti molar ratios and reaction temperatures, were found to have great influence on catalytic activity and polymer properties. Compared with the corresponding mononuclear analogue TiL′, Ti2L showed similar catalytic activity towards ethylene polymerization but produced polymer with lower molecular weight and much wider polydispersities (6.74–20.88), suggesting that two different active centers were present in this binuclear complex.

Binuclear Titanium Catalysts Based on Methylene-Bridged Tridentate Salicylaldiminato Ligands for Ethylene Homo- and Copolymerization

A series of methylene-bridged salicylaldiminato tridentate [ONS] ligands bearing different alkylthio sidearms and the corresponding binuclear titanium complexes (Ti 2 a , Ti 2 b , Ti 2 c ) were synthesized and characterized by elemental analysis, ESI-MS, FT IR, 1H and 13C NMR. To the best of our knowledge, these were the first non-metallocene tridentate binuclear Ti complexes reported. When activated by modified methylaluminoxane (MMAO), these binuclear Ti complexes displayed extremely high activities in the range of 106 g mol−1 h−1 atm−1 for ethylene polymerization and ethylene/α-olefins copolymerization at atmospheric pressure, producing high molecular weight polymers with narrow polydispersity. Both the catalytic behavior and the spectroscopic characterization indicated that the catalysts assumed symmetric structure and contained single-site active species. Most importantly, the catalytic activities towards ethylene (co)polymerization as well as comonomer incorporation ratios were much higher than that of the corresponding mononuclear complexes. Meanwhile, the properties of polymers and the comonomer incorporation ratios can be effectively tuned by the reaction conditions and the alkylthio side group on ligands. Complex Ti 2 c bearing the long octylthio sidearm showed significantly higher activity for ethylene polymerization than the methylthio functionalized Ti 2 a , presumably due to the increased solubility of the catalyst in the reaction medium. While for copolymerization, complex Ti 2 a demonstrated the highest catalytic activity and comonomer incorporation ratio, due the small steric hindrance of the methylthio side group.

ChemInform Abstract: Design of a New Bimetallic Catalyst for Asymmetric Epoxidation and Sulfoxidation.

A new chiral tethered 8-quinolinol-based ligand class is developed. The binuclear titanium complex of the ligand operates through a novel mechanism allowing for the regio- and stereoselective epoxidation of primary and tertiary homoallylic alcohols (up to 98% ee), as well as first examples of 2-allylic phenols (up to 92% ee). The new catalyst system also promotes the asymmetric oxidation of γ-hydroxypropyl sulfides giving an important class of chiral sulfoxides that have been inaccessible to date (up to 95% ee).

Design of a New Bimetallic Catalyst for Asymmetric Epoxidation and Sulfoxidation.

A new chiral tethered 8-quinolinol-based ligand class is developed. The binuclear titanium complex of the ligand operates through a novel mechanism allowing for the regio- and stereoselective epoxidation of primary and tertiary homoallylic alcohols (up to 98% ee), as well as first examples of 2-allylic phenols (up to 92% ee). The new catalyst system also promotes the asymmetric oxidation of γ-hydroxypropyl sulfides giving an important class of chiral sulfoxides that have been inaccessible to date (up to 95% ee).

ChemInform Abstract: Asymmetric Ring Opening of Epoxides with Cyanides Catalyzed by Chiral Binuclear Titanium Complexes.

AbstractTitanium(IV) catalysts generated in situ from Ti(OiPr)4 and BINOL‐based bis salen‐compounds are developed and successfully used as recyclable catalysts for the asymmetric ring‐opening reaction of epoxides with TmsCN.

Asymmetric ring opening of epoxides with cyanides catalysed by chiral binuclear titanium complexes

A series of Schiff bases obtained from salicylaldehydes and 3,3′-diformyl-BINOL were synthesized. The complexes of these Schiff bases with Ti(IV) were active for the asymmetric ring opening of epoxides with TMSCN. A mixture of unpurified ligands was found to be as effective as the best one. The influence of temperature, solvent polarity and structural modification of the pre-catalysts on the enantioselectivity of the process has also been investigated.

Ethylene polymerization using catalysts based on binuclear phenoxyimine titanium halide complexes

Nine new binuclear titanium halide complexes were obtained on the basis of first synthesized tetradentate bis-phenoxyimine ligand precursors with different bridge linkages, including sterically hindered ones, between imine groups. Their binuclear character is confirmed by molecular weights, measured using vapor phase osmometry, MALDI–ToF and diffusion coefficients as determined by NMR–DOSY method. Catalytic activities of catalytic systems on the basis of the binuclear bis-salicylaldimine titanium complexes in ethylene polymerization were investigated. The studied catalytic systems appeared to be rather highly active, (10–70 kg(PE)/[mmol(Ti)·MPa·h]) and considerably more thermostable as compared to mononuclear analogs and made it possible to obtain polyethylenes of high and superhigh molecular weights. The effects of the bridge linkage between imine nitrogens and o-, p-substituents in the phenoxy-group were established.

Fully automated incremental evaluation of MP2 and CCSD(T) core, core-valence and valence correlation energies

A recently proposed coupled cluster evaluation of core–core and core-valence correlation effects within the incremental scheme has been extended to perturbative treatments. The accuracy of the approach is demonstrated at the MP2 and CCSD(T) level of theory for various systems from different areas of chemistry, i.e. a binuclear titanium complex, a diallylmagnesium compound, a Hg 4 cluster and various hydration complexes of the sodium cation. Besides the convergence of individual correlation contributions arising from the core and/or valence electron systems the basis set dependence of the contributions was also monitored. Results within chemical accuracy of 1 kcal/mol in the total energies are typically obtained at third order of the incremental expansion. Furthermore a few reasonable simplifications of the incremental core-valence treatment are proposed, which allow a large number of individual calculations to be omitted a priori without a significant loss of accuracy.