Coordination Sphere Of Titanium Research Articles

INFLUENCE OF SUBSTITUTES ON THE RATE OF THE REACTION OF ORTHOSUBSTITUTED BENZOIC ACIDS WTH ANILINE, CATALYZED BY POLYBUTOXYTITANATES

The polybutoxytitanates catalysis of aniline acylation by orthosubstituted benzoic acids leads to the production of substituted benzanilides. Catalytic rate constants of the second order reaction (the first with respect to aniline and ortho-substituted benzoic acid; boiling ortho=xylene, 145°C) correlate well according to the Hammett and Bronsted equations with straight line segments with ρ=1.93 and α=0.66, in contrast to the reaction of aniline with meta- and parasubstituted benzoic acids and substituted anilines with benzoic acid. This dependence drops out 2=nitrobenzoic and 1=naphthoic acids, which have relatively low reactivity and the greatest steric hindrances both for nucleophilic attack by aniline and for possible coordination with catalytically active centers of the corresponding ortho-substituted titanium polybutoxybenzoates formed in situ.
 Based on these data, the previously proposed mechanism of bifunctional catalysis due to titanium polybutoxybenzoates and their complexes with meta- and parasubstitutedbenzanilides was supplemented by the possibility of the steric inhibition of reaction by the most bulky substituents and chelate structures formation of orthosubstituted benzoic acids and their anilides with individual titanium atoms of the catalyst, as well as the simulta­neous H-bonding of the amino group hydrogen atoms of aniline, which leads to its activation to a nucleophilic attack, with a carbonyl group and an orthopositioned substituent of the orthobenzoate ligand in the coordination sphere of titanium. Taking into account such chelation and steric barriers, as well as inhibition of acid catalysis due to the formation of the imide form of anilides, containing electron-withdrawing substituents, the equations for the rate constants of the catalytic reaction of ortho-substituted benzoic acids with aniline are derived, corresponding to the experimentally obtained Hammett dependence.

Biological Evolution of Titanium(IV) Complex [{(NNO)2Ti}3O3] Bearing Bidentate Heteroditopic Schiff Base Ligand: Synthesis, Structure and Biological Studies

Titanium(IV)-complex of chemical composition [{(NNO)2Ti}3O3] (2) bearing bidentate heteroditopic Schiff base [(C5H4OH)-N=CH-C4H3-NH] (L1) ligand in titanium coordination sphere was reported and its biological significance was evaluated. The in vitro cytotoxicity of L1 and 2 were evaluated by using MTT assay on cancer cell lines (MCF-7 & A549) and observed significant cytotoxicity. Further, the LDH and NO assay studies on both L1 and 2 on cancer cell lines revealed that the enhanced cytotoxicity compared to standard anticancer drug i.e. cisplatin. The DNA binding studies of tested compounds with Ct-DNA molecule by using UV-visible and fluorescence spectra and molecular docking studies revealed that moderate to good binding interactions with test molecules. Thus, the present work contributes and implies the biological significance of Ti-complex (2) and the correlation between the structure and the biological activities of such Ti-complexes supported by Schiff base systems opens up opportunities for further exploitation of similar biologically active titanium systems.

Effects of the Ethoxide in the Coordination Sphere of Titanium on the Performance of MgCl2-Based Ziegler–Natta Catalyst

Traditional formulations of Ziegler–Natta catalysts that are based on magnesium ethoxide tend to generate titanium moieties presenting ethoxide ligand. It is suggested that the ethoxide group in the coordination sphere of titanium affects the catalyst activity and molecular weight distribution of the produced polymer. In the present work, a systematic synthesis of catalyst and chemical characterizations were accomplished with the objective of identifying correlations between the active sites presenting ethoxide as ligand and the performance of the catalyst in terms of activity and average molecular weight. Octahedral and trigonal-bipyramidal titanium moieties were identified as two groups of active sites in the catalyst. The ethoxide group as a ligand of the titanium was found in octahedral moieties only. Trigonal-bipyramidal titanium moieties have preferentially chlorine as ligands.

Titanium Imido Complexes via Displacement of -SiMe3 and C-H Bond Activation in a Ti(III) Amido Complex, Promoted by a Cyclic (Alkyl)(Amino) Carbene (cAAC).

A strong σ-donating cyclic (alkyl)(amino) carbene (cAAC) triggers rearrangement of the silyl(aryl) amido ligand -N(SiMe3)Dipp (Dipp = 2,6-diisopropylphenyl) in the coordination sphere of titanium(III) to afford a novel zwitterionic titanium imido complex with a TiCH2SiMe2[cAAC] linkage. Reduction of this species produces a new DippN=Ti imido complex containing a cAAC-centered radical species, characterized by single crystal diffraction analysis and electron paramagnetic resonance spectroscopy.

Imines in the Titanium Coordination Sphere: η1‐Imine Complexes as Sources of Azavinylidenes and Four‐Membered Imine–Amido‐N,N′ Chelates

In titanium imine complexes the ligand can exhibit several bonding modes. While η2‐imine complexes are intermediates in several catalytic transformations and well investigated, the potential of imines to coordinate through the lone pair of electrons of the nitrogen atom by a dative bond to the titanium center is studied herein. The formation of several bis‐η1 complexes by the reaction of Schiff bases with titanium(IV) chloride was observed. Depending on the substitution pattern of the imine, also complexes with 1:1 stoichiometry are formed. Particular attention is paid to the reaction of imines bearing an SiMe3 group at the nitrogen atom. Titanium complexes of such imines open access to a remarkable N,N′‐bidentate ligand system (4), which can only be obtained in the coordination sphere of the metal atom and cannot be formed by conventional organic synthesis. In this context, imines 2d and 2i were also treated with [CpTiCl3] to yield titanaazavinylidenes 6a and 6b, which may be useful for further modifications.

Imines in the Titanium Coordination Sphere: Highly Reactive Titanaaziridines and Larger Titanacycles Formed by Subsequent C–C Coupling Reactions

AbstractThe reductive complexation of aldimines is one of the promising synthetic tools to obtain titanaaziridines by reaction of the corresponding titanium halides and magnesium as a reducing agent. The effects of the substitution pattern of the imine ligand and the nature of the titanium fragment on the degree of activation of the η2‐coordinated N–C double bond were investigated. With Cp#TiCl3 (Cp# = cyclopentadienyl or pentamethylcyclopentadienyl) as the precursor for the reductive complexation of the imines N‐(4‐methylbenzylidene)aniline (2e) and 2‐methyl‐1‐pyrroline (7), the formation of diazatitanacyclopentanes by McMurry‐like C–C coupling is found. A six‐membered titanacycle 8 is obtained by a Michael‐like coupling reaction of 7. By these insights, it is possible to derive a general reaction pattern for low‐valent titanium centers with imines. Three‐membered titanaaziridines are formed for sterically demanding imines. If such a formation is not possible, coupling reactions occur. Imines that have the opportunity to release a proton at the β‐position to the nitrogen atom undergo Michael‐like reactions, whereas McMurry‐like coupling reactions are found at less‐shielded titanium centers. Although the titanoceneaziridines show the expected reactivity with aldehydes, ketones, and nitriles, the insertion of alkynes into the titanium–carbon bond proceeds with a remarkably inverse regioselectivity compared with that for the methyleneaniline complex [CpAd2Ti(η2‐RN=CH2)] (6; Ad = adamantanyl, R = p‐ClC6H4).

Ammonium-exchanged phase of γ-titanium phosphate

The monoammonium salt of γ-titanium phosphate has been prepared by hydrothermal treatment of π-Ti2O(PO4)2·2H2O in the presence of urea and phosphoric acid, and its crystal structure was obtained by Rietveld analysis using powder X-ray diffraction data. γ-Ti(PO4)(NH4HPO4) crystallizes in the monoclinic space group P21/m with a = 5.0725(3) A, b = 6.3101(3) A, c = 11.2435(5) A, β = 97.980(3)° (Z = 2). The structure consists of 2D titanium phosphate layers in the ab-plane. The titanium atoms and one of the phosphate groups are located nearly in the ab-plane of the layer. All the oxygen atoms of this phosphate group are involved in titanium coordination sphere. The other phosphate group located in the layers edges links two neighboring titanium atoms in the a-direction through two of its oxygen atoms. The remaining two oxygens are pointed toward the interlayer space being involved in hydrogen bond interactions with the ammonium ions. Each ammonium ion is shared by four oxygens belonging to four different phosphate hydroxyl groups. γ-Ti(PO4)(NH4HPO4) is stable until 453 K, while above this temperature, it transforms to γ’-Ti(PO4)(NH4HPO4) high temperature polymorph stable until 573 K. Thermal decomposition of this material leads to cubic TiP2O7 structure, with previous formation of two intermediate pseudo-layered compounds: Ti(PO4)(NH4HP2O7)0.5 and Ti(PO4)(H2P2O7)0.5. The activation energy of thermal decomposition has been calculated as a function of the extent of conversion applying the Kissinger–Akahira–Sunose (KAS) isoconversional method to the thermogravimetric data.

Multidentate Tetrahydrofurfuryloxide Ligand in a Ziegler−Natta Catalyst Studied by Molecular Modeling

The transition from a generation III Ziegler−Natta catalyst with a monodentate Lewis base to a more modern generation IV/V system, containing a tetrahydrofuran derivative, the tetrahydrofurfuryloxide C4H7O−CH2O− bidentate ligand (THFFO), was studied by means of molecular modeling and DFT calculations. This particular ligand was carefully chosen so that it remained in the titanium coordination sphere in the model active site. With such a constraint, the dual role of tetrahydrofurfuryloxide was identified: it was demonstrated how the presence of this ligand limits the number of isomeric active sites as well as enhances the selectivity of the species that can still exist. The results indicate that the catalyst with a bidentate ligand attains good selectivities, albeit at a cost of activity.

TiCl4-Complexation by Mandelic Acid Methylester

The complexes of trinuclear TiCl3-O-TiCl3/TiCl2(O-(R)-mandelic acid methylester)2 I, C18H18Cl8O7Ti3, and dimeric TiCl3O-rac-mandelic acid methylester II, C18H18Cl6O6Ti2, were determined unambiguously by X-ray diffraction. Both crystal structures contain one solvent molecule toluene per complex. In structure I there are five independent complexes in the asymmetric unit cell. The formation of both the crystal structure as well as the coordination sphere of titanium is controlled sensitively by the chirality of mandelic acid methylesters.

Directed reduction of six-membered nitrogen heterocycles--selective formation of polynuclear titanium complexes.

Two, three, four, or eight N-heterocycles react in the coordination sphere of titanium(II) compounds to give polynuclear titanium complexes (see picture, red=TiCp2, blue=N, white=C). Simultaneously occurring CC couplings mark a new strategy for the synthesis of self-assembled compounds of the early transition metals.

Glass Network Evolution with Bi3+/Ti4+ Substitution in Phosphate Glasses Formulated with a Constant Oxygen/Phosphorus Ratio. EXAFS, XANES, and 31P Double Quantum MAS NMR

This paper reports a structural study of the effect of TiO2 substitution for Bi2O3 in xNa2O−xP2O5−yBi2O3−zTiO2 glasses, which were formulated in order to keep a constant average polymerization of the phosphate network. XANES and EXAFS analyses have indicated that the bismuth coordination sphere is similar to that described in other phosphate glasses [Daviero S.; Montagne L.; Palavit G.; Mairesse G.; Belin S.; Briois V. J. Phys. Chem. Solids 2003, 64 (2), 253], and that the titanium coordination sphere is asymmetric, but remains octahedral whatever the substitution degree. 31P double-quantum filtered MAS NMR shows that the Q2 fraction increases with the titanium content in the glasses, thus revealing a repolymerization of the phosphate network. The consideration of charges on oxygens (in terms of valence units) leads to the conclusion that titanium octahedra are coordinated to both Q1 and Q2 sites. The excess charge on these oxygens is compensated by Na+ removed from Q1 sites, which explains the observed repolymerization of the phosphate network. The evolution of glass properties is discussed within the context of this structural model. The increase of glass-transition temperature with titanium substitution for bismuth is due to the repolymerization of the phosphate network. The increase of electrical conductivity with titanium content is attributed to an increase of sodium mobility when it is involved in charge compensation of Ti4+ octahedra.

Preparation of a new type of half-sandwich (alkoxylalkylcyclopentadienyl)titanium trichloride complex and X-ray structural characterization of (CH 3OCH 2CH(CH 3)C 5H 4)TiCl 3

New substituted alkoxylalkylcyclopentadienyl titanium trichloride complexes, CH 3OCH 2CH(CH 3)C 5H 4TiCl 3 ( 3), CH 3OCH(CH 3)CH 2C 5H 4TiCl 3 ( 4) and CH 3OCH 2CH 2CH 2C 5H 4TiCl 3 ( 5) have been synthesized and 3 has been studied by X-ray diffraction. The crystal structure of 3 shows that there is an intramolecular coordination between the ethereal oxygen atom in the side chain on the Cp ring and the titanium atom with an average Ti–O bond length of 2.24 Å. Due to steric limitation around the coordination sphere of titanium, the oxygen atoms in the side chain in complexes 4 and 5 do not coordinate with the central metals.

Interaction of carbon dioxide with the bis(trimethylsilyl)acetylene complex of permethyltitanocene: synthesis and structure of the binuclear carbonate complex of permethyltitanocene (Cp 2∗Ti) 2CO 3

It has been shown that in the interaction of carbon dioxide with the bis(trimethylsilyl)acetylene complex of permethyltitanocene Cp 2 ∗Ti(Me 3SiC 2SiMe 3), full displacement of bis(trimethylsilyl)acetylene from the titanium coordination sphere takes place and carbon dioxide undergoes disproportionation to form Cp 2 ∗Ti(CO) 2 and the binuclear carbonate complex of permethyltitanocene (Cp 2 ∗Ti) 2CO 3. The structure of (Cp 2 ∗Ti) 2CO 3 has been established by X-ray diffraction study. Structural data on the related chlorine-containing carbonate complex Cp 2 ∗Ti(Cl)CO 3TiCp 2 ∗ are also reported.

Titanosilicate Mesoporous Molecular Sieve MCM-41: Synthesis and Characterization

The location and coordination of titanium in the titanosilicate mesoporous molecular sieve MCM-41 prepared from Ti(IV) ethoxide as the source of titanium was studied by XRD, IR spectroscopy, 29Si MAS NMR, and XANES. The results are interpreted on the basis of isomorphous substitution of Ti for Si. XANES shows that titanium is 4-coordinate and that Ti(IV) does not form a regular TiO4 tetrahedron. This is caused by the larger size of the Ti(IV) atom in comparison with Si(IV), resulting in a distortion in the silica matrix, and/or by the presence of H2O in the coordination sphere of titanium. Such distortion is consistent with the line broadening observed in the 29Si MAS NMR spectra, brought about by the wider distribution of the Si−O−Si angles in SiO4 tetrahedra as titanium is progressively incorporated in the silica matrix, and with the changes in the vibrational lattice infrared bands.

ChemInform Abstract: A Sensitive Spectroscopic Probe for Monitoring Changes in the Coordination Sphere of Titanium: Eight‐Membered Dioxatitanacycles and Their Organometallic Derivatives.

AbstractOrganotitanium compounds with oxo ligands are important in organic synthesis and catalytic processes.

Structure of Chloro(cyclopentadienyl)bis(1,2:5,6‐di‐O‐isopropylidene‐α‐D‐glucofuranos‐3‐O‐yl) Titanate, a Novel Titanium‐Carbohydrate Complex

An approach to understanding the enantioselective reactions in the three preceding communications is made possible by the X-ray structure analysis and the 1 H and 13C NM R spectra of the title compound 1. Complex 1 is present as a monomer both in the solid and in solution; its conformation in the two environments is identical. Noteworthy are the different arrangement of the carbohydrate ligands with respect to the Cp ring and the fact that no inversion of the metal center is observed. This allows the formation of a chiral cavity in the coordination sphere of titanium, which might play a key role in the enantioselective reactions of such complexes. (Ti = violet, C1 = green, O = red, C = black).

A Sensitive Spectroscopic Probe for Monitoring Changes in the Coordination Sphere of Titanium: Eight‐Membered Dioxatitanacycles and Their Organometallic Derivatives

In view of the considerable importance of titanium compounds in organic synthesis model studies are especially advantageous. TiCl4 reacts with MBPH2 with evolution of HCl to give [(mbp)TiCl2], an eight-membered heterocycle containing an OTiO unit and oppositely disposed CH2 groups. Its 1 H NMR signals respond sensitively to changes at the Ti atom which are caused, e.g., by alkylations and arylations and by increasing the coordination number.

Thermolysis of di-π-cyclopentadienyl-σ-organotitanium chlorides

The thermolysis of a series of compounds Cp 2(R)TiCl (where Cpπ-cyclopentadienyl and R is a σ-bonded hydrocarbon moiety) was studied. After an initial unsteady period, first-order loss of the R group was observed. The activation energy of bond breaking was approximately 25 kcal/mole for all compounds. The products and kinetics are explained by postulating that the rate-determining step is the promotion of the R group to a non-ionic activated state in which it is still within and influenced by the titanium coordination sphere but mobile enough to migrate from one titanium atom to another.