Titanyl Complexes Research Articles

Titanyl complexes with 1,10-phenanthroline-based diols

Titanyl complexes with 1,10-phenanthroline-based diols

Terminal Titanyl Complexes of Tri- and Tetrametaphosphate: Synthesis, Structures, and Reactivity with Hydrogen Peroxide.

The synthesis and characterization of tri- and tetrametaphosphate titanium(IV) oxo and peroxo complexes is described. Addition of 0.5 equiv of [OTi(acac)2]2 to dihydrogen tetrametaphosphate ([P4O12H2]2-) and monohydrogen trimetaphosphate ([P3O9H]2-) provided a bis(μ2,κ2,κ2) tetrametaphosphate titanyl dimer, [OTiP4O12]24- (1; 70% yield), and a trimetaphosphate titanyl acetylacetonate complex, [OTiP3O9(acac)]2- (2; 59% yield). Both 1 and 2 have been structurally characterized, crystallizing in the triclinic P1̅ and monoclinic P21 space groups, respectively. These complexes contain Ti≡O units with distances of 1.624(7) and 1.644(2) Å, respectively, and represent rare examples of structurally characterized terminal titanyls within an all-oxygen coordination environment. Complexes 1 and 2 react with hydrogen peroxide to produce the corresponding peroxotitanium(IV) metaphosphate complexes [O2TiP4O12]24-(3; 61% yield) and [O2TiP3O9(acac)]2- (4; 65% yield), respectively. Both 3 and 4 have been characterized by single-crystal X-ray diffraction studies, and their solid-state structures are presented. Complex 3 functions as an oxygen atom transfer (OAT) reagent capable of oxidizing phosphorus(III) compounds (P(OMe)3, PPh3) and SMe2 at ambient temperature to result in the corresponding organic oxide with regeneration of dimer 1.

Structure of a Hydrated Sulfonatotitanyl(IV) Complex in Aqueous Solution and the Dimethylsulfoxide Solvated Titanyl(IV) Ion in Solution and Solid State

The coordination chemistry of oxotitanium(IV) or titanyl(IV), TiO2+, has been studied in solution by X-ray methods. The titanyl(IV) ion hydrolyzes easily in aqueous systems to solid titanium dioxide as long as it is not stabilized through complexation. In this study the structures of the hydrated bissulfatotitanyl(IV) complex and the dimethylsulfoxide (DMSO) solvated titanyl(IV) ions have been determined. In isolated monomeric titanyl complexes titanium(IV) binds strongly to a doubly bound oxo group at ca. 1.64 Å, to four ligands in the equatorial plane almost perpendicular to the Ti=O bond at ca. 2.02 Å, and there is one weakly bound ligand, trans to the Ti=O bond, at ca. 2.22 Å, for oxygen donor ligands; the O=Ti–Oeq bond angles are 95°–100°. The structure of the DMSO solvated titanyl(IV) ion in the solid state is maintained in DMSO solution.

Titanium complexes based on pyridine containing dialcohols: Effect of a ligand

Substituted 2,6-bis(hydroxyalkyl)pyridines, H2L, 1–3 (2,6-Py(CH2(X)OH)(CH2(Y)OH), X=Y=cyclo-C6H10, 1; X=Y=1-Ad, 2; X=CPh2, Y=CH2CPh2, 3), were used as ligands for the synthesis of titanium(IV) complexes, (i-PrO)2Ti(L), 1a–3a. On the contrary, application of related dialcohol based on 2,2′-bipyridine, H2L′, 5 (2,2′-bipy-6,6′-(CH2Ph2OH)2), resulted in titanyl complex, (L′)TiO, 6. The molecular structure of 6 was investigated by X-ray analysis. Compounds 1a and 3a were tested as initiators in ring-opening polymerization of l-lactide and ε-caprolactone showing moderate activity.

NMR and DFT study of chemical bonding of the titanyl ion in pentafluoro complexes (NH4)3TiOF5 and Rb2KTiOF5

19F NMR and DFT methods are used to study the electronic structure and chemical bonding of titanyl ions in pentafluoro titanyl complexes (NH4)3TiOF5 and Rb2KTiOF5. The experimental values of the anisotropy of 19F NMR chemical shifts (CSs) are shown to be consistent with the calculated parameters within the DFT method. At normal temperatures orientational disordering of octahedral [TiOF5]3- anions occurs, fluorine atoms steadily occupying cis- and trans-positions with respect to the O2- ion. In both complexes, trans-position is not fully occupied; the occupation ratio does not exceed ~4:0.9. When the temperature is decreased to 150 K, the value of the CS anisotropy of the fluorine atom resonance line in trans-position is found to be smaller than the dipole-dipole broadening, whereas the line from fluorine atoms in cis-positions transforms into an asymmetric broad line characterized by the triaxial anisotropy of the CS tensor. It is shown that the found anisotropy corresponds to violation of the axial symmetry of Ti—F cis bonds because of strong delocalization of the electron density of Ti—O bonds in the titanyl ion.

Condensation of β‐Diester Titanium Enolates with Carbonyl Substrates: A Combined DFT and Experimental Investigation

The condensation of dialkyl beta-diesters with various aldehydes promoted by TiCl4 has been studied by DFT approaches and experimental methods, including NMR, IR and UV/Vis spectroscopy. Various possible reaction pathways have been investigated and their energy profiles evaluated to find out a plausible mechanism of the reaction. Theoretical results and experimental evidence point to a three-step mechanism: 1) Ti-induced formation of the enolate ion; 2) aldol reaction between the enolate ion and the aldehyde, both coordinated to titanium; and 3) intramolecular elimination that leads to a titanyl complex. The presented mechanistic hypothesis allows one to better understand the pivotal role of titanium(IV) in the reaction.

Effect of aluminum on Ti-coordination in silicate glasses: A XANES study

The structure of glasses in the K2O-Al2O3-TiO2-SiO2 system was investigated using XANES spectroscopy. Glass samples, synthesized by quenching in air from high temperature fusions, represent the addition of Al2O3 to a base of composition K2TiSi4O11 in amounts corresponding to 0.25, 0.50, 0.75, 1.00, 1.25, and 1.50 mol p.f.u. In the Ti-free system, this range of alkali/aluminum ratios crosses the leucite stoichiometry at 1.0. Si K-edge and Al K-edge spectra indicate tetrahedral environments for these elements, and show no variations related to coordination change as a function of Al content. Changes in the relative intensities of peaks in the Al K-edge, however, suggest variation in the intertetrahedral (T-O-T) angle. We associate the decrease of this angle for the glasses of peraluminous composition with the presence of triclusters of tetrahedra. The pre-edge peak absorption features in the Ti K-edge XANES spectra indicate that the average Ti coordination decreases with the addition of Al2O3. We infer depletion of fivefold-coordinated titanium (possibly as alkali titanyl complexes), which are dominant in the Al-free glass, by the formation of fourfold coordinated Ti and alkali aluminate complexes (up to a concentration of 40% in the most peraluminous glass). Significant amounts of [V]Ti remain present, even at peraluminous compositions, in further support of tricluster formation as a mechanism for Al incorporation.

Do titanyl groups exist in titanium silicates? An experimental study

Two synthetic routes have been investigated, aimed at the preparation of silica-supported titanyl (>TiO) and titanol (>Ti(OH) 2) groups, the latter corresponding to the hydrated form of the titanyl group. In the first synthetic route, the titanyl complex TiOCl 2(NMe 3) 2 was reacted with an aerosil, and the resulting material thermally treated to remove residual Cl and NMe 3 ligands. In an alternative route, silica (aerosil and silica-gel) was reacted with Ti(CH 2Ph) 4 to afford mainly anchored >Ti(CH 2Ph) 2 moieties, which were subsequently hydrolysed. Characterization of the resulting materials using a combination of surface analytical techniques revealed that in all cases at least two titania phases were obtained, corresponding to isolated tetrahedral Ti sites, and an amorphous form of TiO 2 containing six-coordinate titanium. For the syntheses based on Ti(CH 2Ph) 4, UV-vis and XPS data indicated that the relative proportion of the two phases formed was dependent on the support employed, aerosil affording predominantly (≡SiO) 2Ti(OH) 2 sites. No evidence was found for the presence of three-coordinate titanyl species, >TiO, even when the aerosil-supported >Ti(OH) 2 sites were calcined at 500°C. It is, therefore, concluded that titanyl groups are unlikely to be present in significant concentrations in titanium silicates. When tested in the epoxidation of 1-octene with tert-butyl hydroperoxide, the model systems were found to display epoxidation activity comparable with that of a wide-pore Ti–zeolite, Ti-MCM-41. The observed turnover frequency was found to increase with increasing dispersion of the titania, consistent with the notion that isolated, Lewis acidic Ti(IV) centres are the most active sites for epoxidation catalysis.

Sulfur dioxide as a chemical probe for titanyl groups in titanium silicalites

The reaction of titanyl (TiO) groups with SO 2, which for molecular titanyl complexes is found to occur readily at room temperature, has been used to test for the presence of titanyl groups in titanium silicalite (TS-1) and Ti-MCM-41. Exposure of samples to SO 2 does not lead to any reduction in the intensity of the characteristic IR band observed at 960 cm −1, implying that this absorption is not associated with the presence of titanyl groups.

New Heterobinuclear μ-Oxo-Bridged Dimer Complexes: Synthesis, Characterization and Structural Studies of a Macrocyclic Titanyl Complex and its Adducts

The titanyl complex, TiO(C22H22N4), a complex of the ligand (I) obtained by the hydrolysis of the corresponding dichloride, has a reactive Ti=O function which readily interacts with other metal species forming μ-oxo heterobinuclear dimers. In these adducts, the Ti=O functions as a base toward oxophilic metal centres such as Fe(lII) and as a π-acid, analogous to the carbonyl group, forming an adduct with a low valent species such as the Mo(CO)5 group, yielding a Ti(IV)-O-Mo linkage. Crystals of the titanyl complex, TiO(C22H22N4).C2O2H6, are monoclinic, P21/C with a = 23.083(3), b = 7.740(7), c = 23.208(5) Å, β = 96.54. (2) and d(calcd) = 1.443 g cm −3 for Z = 4. The Ti=O distance is 1.653(3) Å with a large displacement of 0.754(3) Å for the Ti atom from the N4 macrocyclic coordination plane. The adduct of the titanyl complex with Fe(SALEN)Cl, SALEN = (salicylaldimine)ethylenediamine, in the presence of NaB(C6H5)4 yields a μ-oxo-heterobinuclear complex_of stoichiometry (C22H22N4)Ti-O-Fe- (SALEN)B(C6H5)4. Crystals of the complex are triclinic, P1 with a = 13.122(4), b = 13.883(12), c = 14.539(5) Å, a = 94.21(5), β = 93.08(3), γ = 99.46(3)° with d(calcd) = 1.336gem−3 for Z = 2. In addition to the expected dimeric Ti-O-Fe structure, weak interactions between the SALEN oxygen atoms and the iron atom of the centrosymmetrically related Fe(SALEN) group yields a tetrameric cluster, The Ti-O distance of the Ti-O-Fe linkage is lengthened to 1.706(4) Å and the Fe-O distance is 1.935(6) Å with the Ti-O-Fe angle 160.9(2)°. The Fe-O “intramolecular” interaction distance, 2.178 Å, is indicative of a weak bond.

The oxalato complexes of titanium(IV)—II: Precipitation with lead(II) in 0.5 M NaClO 4 solution

Titration studies of ammonium titanyl oxalate solutions with Pb(NO 3) 2 at an ionic strength of 0.5 M (NaClO 4) have shown that at pH > 1.5 precipitates are formed consisting of three compounds: PbTiO(C 2O 4) 2·4H 2O, PbC 2O 4 and Ti(OH) 4. The solubility product of lead titanyl oxalate (PTO) is (35 ± 2) times the solubility product of lead oxalate, i.e. log K PTO = −6.90 ± 0.03, when log K PO = −8.45 for lead oxalate as found by Klatt. The solubility product [Ti(OH) 2 2+][OH −] 2 was found to have the value log K TH = −30.5 ± 0.25. At low pH lead oxalate and titanium hydroxide dissolve. It is necessary to include a lead titanyl complex of unknown nature in calculation models for simulating equilibrium concentrations during titrations in order to explain the anomalously high dissolved lead(II) concentration. The solubility product calculated for PTO is not very sensitive to the different models. Lead and titanium contents of solutions equilibrated with solid PTO differed from the expected values based on the models for titrations. A satisfactory explanation for the low Ti(IV) and high Pb(II) concentrations can not yet be given.

Synthese et proprietes de quelques porphyrines de titanyle

Titanyl complexes of several porphyrins are obtained in good yield by treating the corresponding free bases with titanium tetrachloride. Rotation of phenyl rings in titanyltetraarylporphyrins has been studied by variable temperature 1H NMR. An electrochemical study shows two anodic and two cathodic electron transfer steps which affect the macrocycle, not the metal ion. The titanyl group in these compounds is inert toward numerous reagents.

Dimethyl sulphoxide complexes of titanyl, zirconyl and thorium perchlorates

TiO·5DMSO(ClO 4) 2, ZrO·8DMSO(ClO 4) 2 and Th·12DMSO(ClO 4) 4 are prepared by reaction of the respective metal perchlorates with an excess of dimethyl sulphoxide. The last two complexes yield ZrO·6DMSO(ClO 4) 2 and Th·6DMSO(ClO 4) 4 on heating around 185°C, while the titanyl complex explodes at 190°C. The extra DMSO molecules in the zirconyl and thorium complexes seem to be held in the lattice. In the parent complexes, the co-ordinated DMSO molecules are bonded by oxygen to the metal atoms while in the DMSO complexes of zirconyl and thorium perchlorates, obtained by heating at 185°C, the bonding involves the sulphur, indicating a change in the bonding during the process of heating.