Ti Complexes Research Articles

Syntheses and Characterization of Ti(III)/Ti(IV) Triazenido Complexes

AbstractThe syntheses of side‐on Ti(III) triazenido complexes via the ethylene complexes Cp*Ti(η2‐C2H4)(η5‐C5H4CR2H) and side‐on Ti(IV) triazenido complexes via bis(π‐η5 : σ‐η1‐pentafulvene) titanium complexes are reported. The deprotonation of the triazene N−H function occurs under mild conditions either by reduction of the proton to hydrogen mediated via the masked titanocene (II) of the ethylene complex or by the nucleophilic Cexo atom of the pentafulvene moiety. The structures of the paramagnetic Ti(III) complexes were confirmed by single‐crystal X‐ray diffraction, whereas the diamagnetic Ti(IV) complexes were characterized via NMR spectroscopy and additionally, Ti2 c by single‐crystal X‐ray diffraction. The structure of complex Ti2 c reveals one of the smallest bent angles known for titanium pentafulvene complexes.

Radiochemical isolation of 45Ti using ion chromatography

45Ti exhibits favorable decay properties for positron emission tomography (PET) imaging and can be easily produced by the bombardment of natural scandium (Sc) by protons using the 45Sc(p,n)45Ti nuclear reaction. However, separation of 45Ti from irradiated Sc targets is arduous due to the hydrolytic instability of Ti(IV) complexes, making it a significant bottleneck for routine application of this radionuclide. In the present work, we describe the development and optimization of an ion chromatographic separation method based on trapping of 45Ti on a hydroxamate-functionalized chelating resin and subsequent elution with oxalic acid at pH = 2.8. Under optimized conditions, this method enabled 45Ti-recovery of 61 ± 8% within 7 min. Sc contamination in scaled-up experiments was found to be only 3.0 ± 1.8 µg/mL. The resulting 45Ti-solution was directly used for complexation with CDTA as a model chelator, affording the corresponding [45Ti]Ti(cdta) complex with a radiochemical conversion of 73 ± 3%. Conclusively, this promising method could be transferred to automated synthesis modules and should enable the preparation of 45Ti-labeled compounds for PET imaging.

Coordination-induced bond weakening and small molecule activation by low-valent titanium complexes.

Bond activation of small molecules through coordination to low valent metal complexes in M⋯X-H type interactions (where X = O, N, B, Si, etc.) leads to the formation of unusually weak X-H bonds and provides a powerful approach for the synthesis of target compounds under very mild conditions. Coordination of small molecules like water, amides, silanes, boranes, and dinitrogen to Ti(III) or Ti(II) complexes results in the synergetic redistribution of electrons between the metal orbitals and the ligand orbitals which weakens and enables the facile cleavage of the X-H or N-N bonds of the ligands. This review presents an overview of coordination-induced bond activation of small molecules by low valent titanium complexes. In particular, the applications of low valent titanium-induced bond weakening in nitrogen fixation are presented. The review concludes with potential future directions for work in this area including low-valent Ti-based PCET systems, photocatalytic nitrogen reduction, and approaches to tailoring complexes for optimal bond activation.

A comparative study of titanium complexes bearing 2-(arylideneamino)phenolates and 2-((arylimino)methyl)phenolates as catalysts for ring-opening polymerization of ε-caprolactone and L-lactide.

Titanium complexes bearing 2-(arylideneamino)phenolates and 2-((arylimino)methyl)phenolates were synthesized, and their catalytic activities in the polymerization of ε-caprolactone and L-lactide were studied. Among five-membered ring Ti complexes bearing 2-(arylideneamino)phenolates, FCl-Ti exhibited the highest level of catalytic activity ([CL] : [FCl-Ti] = 100 : 1, where [CL] = 2 M, and conv. = 86% at 60 °C after 9 h). For six-membered ring Ti complexes bearing 2-((arylimino)methyl)phenolates, SCl-Ti exhibited the highest level of catalytic activity ([CL] : [SCl-Ti] = 100 : 1, where [CL] = 2 M, and conv. = 88% at 60 °C after 118 h). The five-membered ring Ti complexes bearing 2-(arylideneamino)phenolates exhibited a higher level of catalytic activity (6.1-12.8 fold for the polymerization of ε-caprolactone and 6.2-23.0 fold for the polymerization of L-lactide) than the six-membered ring Ti complexes bearing 2-((arylimino)methyl)phenolates. The density functional theory (DFT) results revealed that the free energy of the first transition state FH-Ti-TS1 is 36.49 kcal mol-1 which is lower than that of SH-Ti-TS1 (46.58 kcal mol-1), which was ascribed to the fact that the Ti-Nim bond (2.742 Å) of FH-Ti-TS1 is longer than that of SH-Ti-TS1 (2.229 Å) and reduces the repulsion between ligands.

Influence of the N–H functionality on activating O,N,N-titanium complexes and controlling polyethylene molecular weights and distributions

Ti complexes supported by O,N,N-ligands show unprecedented activity in ethylene polymerization and produce polymers with unimodal/narrow or bimodal/broad distributions, depending upon amine-N substituents and catalyst pre-activation or not.

Flexible NHC-aryloxido aluminum complex and its zwitterionic imidazolium aluminate precursor in ring-opening polymerization of ε-caprolactone.

Anionic donor-functionalized NHC (N-heterocyclic carbene) complexes of Al are rare. We report one such case here, an NHC-aryloxido AlMe2 complex [Al(L)Me2] (2), following a stepwise synthesis from the proligand [HO-4,6-tBu2-C6H2-2-CH2{CH(NCHCHNAr)}]Br [LH2Br; Ar = 2,6-iPr2-C6H3 (Dipp)] and AlMe3via the zwitterionic intermediate [Al(LH)Me2Br] (1). The ligand's flexibility in 2 is evident from the conformational fluxionality revealed by VT-1H NMR spectroscopic analysis. The ∠O-Al-C (ca. 100.5°) bite angle is also wider than the ∠O-Ti-C (ca. 80.6°) as seen in our recently reported Ti complex [Ti(L)(NMe2)2Br]. DFT analysis showed that the CNHC-Al bond is significantly ionic, as is the CNHC-Ti bond. Both 1 and 2 are active in the ring-opening polymerization (ROP) of ε-caprolactone (CL). 2, similar to [Ti(L)(NMe2)2Br], exhibits bifunctional MLC-type monomer activation, but only at an elevated temperature. However, the 2/BnOH combination is catalytically active at room temperature, likely through a zwitterionic [Al(LH)Me2(OBn)]. The 1/BnOH combination follows a similar mechanism but surprisingly at a faster rate.

Hexacyclotetradecenes as polycyclic fused exo-norbornene monomers: synthesis of cyclic olefin copolymers via Ti-catalyzed controlled polymerization

An isomeric mixture of hexacyclotetradecenes was (co)polymerized (with 1-octene) using a Ti complex catalyst to produce new cyclic olefin copolymers.

Microstructure evolution and fracture behavior of Ti–6Al–4V fabricated by WAAM-LDM additive manufacturing

WAAM and LDM are two typical DED technologies. WAAM-LDM additive manufacturing technology can achieve the purpose of producing large and complex Ti–6Al–4V components, improving processing efficiency and precision. However, there is a lack of in-depth research on the microstructure evolution mechanism and the fracture behavior of WAAM-LDM samples. Therefore, horizontal and vertical WAAM samples were invoked as the substrate for LDM processes in this study, and the mechanical properties and tensile fracture behavior under different load directions were evaluated. The results show that the samples fabricated by WAAM-LDM manufacturing consist of four zones: WAAM zone, heat affected zone (HAZ), remelting zone (RZ) and LDM zone. WAAM zone mainly composed of coarse colony structure, HAZ and RZ are dominated by α colonies and fine basketweave structure, respectively, and LDM zone consists of acicular α phases and fine basketweave structure. The thickness of α laths shows a trend of ‘WAAM > HAZ > LDM > RZ’. The strengths are greatly improved at the interfaces due to the good metallurgical bonding and finer microstructure. All the fractures locate at WAAM zone during tensile test and propagate along the basketweave structure. These strengths of WAAM-LDM samples under the action of horizontal loading are higher than that of WAAM samples, and all the elongations of WAAM-LDM samples are higher than 10 %.

Pyrrole-Based Ti(III) and Ti(IV) PNP Pincer Complexes: Insertion of Ketones into the Ti(IV)-Phosphorus Bond.

The synthesis, characterization, and reactivity of pyrrole-based Ti(III) and Ti(IV) PNP pincer complexes are described. [P(NH)P-iPr] (1) reacts with [TiCl4(THF)2] at room temperature in the presence of NEt3 to afford the Ti(IV) complex [Ti(PNPiPr)(Cl)3]. This complex reacts with acetone and cyclopentanone to give complexes [Ti(PNOacet-iPr)(Cl)3] and [Ti(PNOcyclo-iPr)(Cl)3], respectively. Insertion of the ketone into the Ti(IV)-P bond took place, forming a new tridendate PNO-ligand. Treatment of [TiCl3(THF)3] with the lithium salt of [P(NH)P-iPr] afforded, upon workup, complex [Ti(PNP-iPr)(Cl)2(THF)], a paramagnetic complex with an μeff value of 1.8(1) μB which corresponds to one unpaired electron and a formal oxidation state of +III. This compound does not react with ketones. A mechanistic proposal based on DFT calculations is presented. Ketone insertion proceeds via an associative reaction initiated by ketone coordination at the metal center, followed by the opening of the five-membered chelate ring, and finally an intramolecular nucleophilic attack of the noncoordinated phosphine arm at the carbonyl atom of the ketone. All complexes were characterized by X-ray crystallography.

Ti(IV) Complexes with OSSO-Type Diol Ligands as Catalysts for Synthesis of Ultrahigh-Molecular-Weight Polyethylene and Ethylene–Propylene Copolymers

Ti(IV) Complexes with OSSO-Type Diol Ligands as Catalysts for Synthesis of Ultrahigh-Molecular-Weight Polyethylene and Ethylene–Propylene Copolymers

Synthesis and structural characterization of Ti(III) and Mo(III) complexes supported by PNP pincer ligands

New Ti(III) and Mo(III) complexes of formulae [(PNP-Ph)TiCl3], 1, and [(PNP-iPr)MoCl3], 2, where PNP-Ph = N,N’-bis(diphenylphosphino)-2,6-diaminopyridine and PNP-iPr = N,N’-bis(diisopropylphosphino)-2,6-diaminopyridine were synthesised, in moderate yields, by reaction of MCl3·(THF)3 (M = Ti and Mo) with the suitable ligand precursor. The solid-state molecular structures of complexes 1 and 2 were obtained by single-crystal X-ray diffraction. Crystal data for C37H41Cl3N3O2P2Ti (1·(C4H8O)2): triclinic, space group P-1 (no. 2), a = 10.0945(4) Å, b = 10.3002(4) Å, c = 18.6233(7) Å, α = 92.412(2)°, β = 91.108(2)°, γ = 101.705(3)°, V = 1893.65(13) Å3, Z = 2, µ(MoKα) = 0.559 mm-1, Dcalc = 1.361 g.cm-3, 20760 reflections measured (2.021 ≤ Θ ≤ 27.130), 8327 unique (Rint = 0.0399, Rsigma = 0.0414) which were used in all calculations. The final R1 was 0.0316 (I > σ(I)) and wR2 was 0.0850 (all data). Crystal data for C17H33Cl3MoN3P2 (2): tetragonal, space group I41/a (no. 88), a = b = 19.468(4) Å, c = 31.711(6) Å, α = β = γ = 90°, V = 12019(5) Å3, Z = 16, µ(MoKα) = 0.816 mm-1, Dcalc = 1.202 g.cm-3, 42367 reflections measured (2.569 ≤ Θ ≤ 25.347), 5498 unique (Rint = 0.1408, Rsigma = 0.1293) which were used in all calculations. The final R1 was 0.1005 (I > σ(I)) and wR2 was 0.3194 (all data). The coordination geometry around the titanium and molybdenum centers is best described as octahedral, with three donor atoms of the PNP ligand and one chlorine atom occupying the equatorial plane. The axial positions of the octahedron are occupied by the other two chlorido ligands in both complexes. The NH spacer groups in the PNP ligands have an important role in the establishment of hydrogen bonds between the complexes and molecules of the solvent or neighbouring species.

The Recovery of TiO2 from Ilmenite Ore by Ammonium Sulfate Roasting–Leaching Process

TiO2 production is a key part of Ti metallurgy and Ti recycling, and the process itself has turned out to be energy-consuming and material-consuming. New technologies are needed to utilize complex Ti ores, such as ilmenite, and reduce the carbon footprint of TiO2 extraction. Ammonium sulfate roasting has been revealed as an efficient way to carry out phase transformations of complex minerals. A low-temperature sulfation roasting approach was studied to chemically breaking down the crystal structure of ilmenite and generate metal soluble sulfates simultaneously. These roasted products were introduced to water leaching, then the residue of the water leaching was leached by diluted HCl acid, and the TiO2 product was enriched in the leaching residue. The effects of roasting temperature, roasting time, ilmenite-to-ammonium sulfate mass ratio, ilmenite particle size, and second-stage roasting on iron removal and titanium loss leaching efficiency were systematically studied. The results show that the optimum roasting conditions were a roasting temperature of 500 °C, a roasting time of 210 min, an ilmenite-to-(NH4)2SO4 mass ratio of 1:7, and an ilmenite particle size of below 43 µm. Under optimized conditions, the TiO2 grade in the obtained synthetic rutile reached 75.83 wt.%. Furthermore, the phase transformation and reaction mechanism during roasting are discussed and interpreted.

The spectroscopic properties and capability of a new and selective complex of Ti-Plumbagin for analyzing titanium in sand samples

A novel Ti-PLB compound, a complex of titanium (Ti) and plumbagin (PLB) in acidic medium, has been synthesized for the first time and investigated via fluorescence spectroscopy. This complex's fluorescence demonstrated that it emits and excites light at wavelengths of 605 nm and 500 nm, respectively. It has a stable fluorescence intensity after 3 min, a stable mol ratio of Ti to PLB of 1:2, a pH range of 4–6, binding constants of K = 3.98 × 10+4 and is extremely selective for Ti. It has also been properly stabilized in ethanol. Fluorescence spectroscopy, UV–vis, FT-IR, 1H NMR, 13C NMR, HSQC, HMBC, HR-MS, X-rays, XPS, TGA, SEM-EDX, and TEM have all pointed to a complex structure, Ti (PLB)2. This article invented it to determine the optimal conditions, and the sand sample analysis has also been applied in this project, with conclusions that are compatible with the results of the ICP-OES methodology and the DFT calculation explains the fluorescence mechanism of Ti(PLB)2 complex. Fluorescence spectroscopy has been established as a novel method to analyze Ti that is based on the complex of Ti (PLB)2 in EtOH: H2O = V:V = 7:3 and it has demonstrated advantages such as simplicity, selectivity, high sensitivity, and appropriate solvent. The values of the LOD and LOQ of Ti (IV) at pH of 5.0 are 2 × 10−7 M and 7 × 10−7M. The intermediate precision (relative standard deviation (RSD), %) was 4.09%. The proposed method has the advantages of being very selective, high sensitivity, fluorescence complexes forming instantaneously, and simpler analytical equipment and the results give the same accuracy.

Charge Transfer Kinetics of the Ti(IV)/Ti(III) Redox Couple in the Cesium Chloride-Cesium Fluoride Melt with Addition of Alkaline Earth Metal Cations

The electrochemical behavior of the Ti(IV)/Ti(III) redox couple in the CsCl-CsF(10 wt%)-K2TiF6 melt was studied by cyclic voltammetry. The diffusion coefficients of the Ti(IV) complexes were calculated using the Randles-Sevcik equation. The standard rate constants of charge transfer for the Ti(IV)/Ti(III) redox couple in the CsCl-CsF(10 wt%)-K2TiF6 melt without and with additions of alkaline Earth metal cations (Mg2+, Ca2+, Sr2+, Ba2+) were determined. It was found that the rate constants of charge transfer increase with increasing ionic potential of the addition, reaching a maximum value for complexes with outer-sphere cations of magnesium, and this dependence is rectilinear. The activation energies of the charge transfer process in melts with additions of alkaline Earth metal cations were calculated and these values are significantly lower than the activation energy of the initial system CsCl-CsF(10 wt%)-K2TiF6. The kinetic parameters of the Ti(IV)/Ti(III) redox couple in chloride-fluoride melts with different second coordination sphere composition of the complexes were compared.

Structural Speciation of Ti(IV)-(α-Hydroxycarboxylic Acid) Complexes in Metabolism-Related (Patho)Physiology-In Vitro Approaches to (Pre)Adipocyte Differentiation and Mineralization.

The prospect of developing soluble and bioavailable Ti(IV) complex forms with physiological substrates, capable of influencing (patho)physiological aberrations, emerges as a challenge in the case of metabolism-related pathologies (e.g., diabetes mellitus 1 and 2). To that end, pH-specific synthetic efforts on binary Ti(IV)-(α-hydroxycarboxylic acid) systems, involving natural physiological chelator ligands (α-hydroxy isobutyric acid, D-quinic acid, 2-ethyl-2-hydroxybutyric acid) in aqueous media, led to the successful isolation of binary crystalline Ti(IV)-containing products. The new materials were physicochemically characterized by elemental analysis, FT-IR, TGA, and X-ray crystallography, revealing in all cases the presence of mononuclear Ti(IV) complexes bearing a TiO6 core, with three bound ligands of variable deprotonation state. Solution studies through electrospray ionization mass spectrometry (ESI-MS) revealed the nature of species arising upon dissolution of the title compounds in water, thereby formulating a solid-state-solution correlation profile necessary for further employment in biological experiments. The ensuing cytotoxicity profile (pre-adipocytes and osteoblasts) of the new materials supported their use in cell differentiation experiments, thereby unraveling their structure-specific favorable effect toward adipogenesis and mineralization through an arsenal of in vitro biological assays. Collectively, well-defined atoxic binary Ti(IV)-hydroxycaboxylato complexes, bearing bound physiological substrates, emerge as competent inducers of cell differentiation, intimately associated with cell maturation, thereby (a) associating the adipogenic (insulin mimetic properties) and osteogenic potential (mineralization) of titanium and (b) justifying further investigation into the development of a new class of multipotent titanodrugs.

Oxidation Effects on Short-Term Creep Response in Air of Commercially Pure Titanium (CP-2 Ti)

The creep response in the air of commercially pure titanium was investigated at 550, 600, and 650 °C to assess the effect of oxidation on the mechanical response. Experiments demonstrated that prolonged exposures at high temperatures produced a marked reduction in the minimum creep rate under a given applied stress. Microhardness measurements showed that a hardened zone formed in proximity to the surface due to oxygen penetration into the metal. A simplified composite model was then used to describe the creep response. In this model, the sample consisted of two zones, the hard case that was enriched in oxygen and the soft pure-titanium core, both creeping with similar strain rates. Calculations led to an estimation of the dependence of the minimum creep rate on stress and temperature for the hard high-oxygen zone. The simplified composite model presented here provided a good description of the experimental creep data for pure titanium, tested in its air, and a reliable picture of the effect of oxidation on complex Ti alloys.

Titanium(II) as a Fuel Atom in Energetic Materials.

The energetic content of the compounds MgTp2, FeTp2, MnTp2, and TiTp2 is measured by bomb calorimetry and compared to theoretical calculations (Tp = trispyrazoylborate). TiTp2 had the largest heat of combustion of the four compounds. Comparison of the heat of combustion of the Ti complex to those of Mg and Mn complexes suggests an effective combustion energy of TiII of between 1400 and 3000 kJ/mol, affirming the role of TiII as a strong fuel atom.

General Synthesis of MTiO3 (M = Ba, Sr, Ca, Zn, and Mg) Using Water-soluble Ti complexes

A general and simple approach was developed for the synthesis of nanosized titanium-based perovskites (MTiO3). A water-soluble Ti complex and the acetate of the relevant A-site metal were dissolved in water and dried to obtain a solid precipitate. The low-temperature calcination of the precipitate yielded MTiO3 (M=Ba, Sr, Ca, Zn, and Mg) with specific surface areas as high as those of previously reported MTiO3. A general and simple approach was developed for the synthesis of nanosized titanium-based perovskites (MTiO3) using a water-soluble Ti complex.

Improving a Methane C-H Activation Complex by Metal and Ligand Alterations from Computational Results.

We present results for a series of complexes derived from a titanium complex capable of activating C-H bonds under mild conditions (PNP)Ti═CHtBu(CH2tBu), where PNP = N[2-PiPr2-4-methylphenyl]2-. In addition to the initial activation of methane, a tautomerization reaction to a terminal methylidene is also explored due to methylidene's potential use as a synthetic starting point. Analogous complexes with other low-cost 3d transition metals were studied, such as scandium, titanium, vanadium, and chromium as both isoelectronic and isocharged complexes. Our results predict that V(IV) and V(V) complexes are promising for methane C-H bond activation. The V(V) complex has a low rate-determining barrier for methane activation, specifically 16.6 kcal/mol, which is approximately 12 kcal/mol less than that for the Ti complex, as well as having a moderate tautomerization barrier of 29.8 kcal/mol, while the V(IV) complex has a methane activation barrier of 19.0 kcal/mol and a tautomerization barrier of 31.1 kcal/mol. Scandium and chromium complexes are much poorer for C-H bond activation; scandium has very high barriers, while chromium strongly overstabilizes the alkylidene intermediate, potentially stopping the further reaction. In addition to the original PNP ligand, some of the most promising ligands from a previous work were tested, although (as shown previously) modification of the ligand does not typically have large effects on the activity of the system. Our best ligand modification improves the performance of the V(V) complex via the substitution of the nitrogen in PNP by phosphorus, which reduces the tautomerization barrier by 5 to 24.4 kcal/mol.

An anticancer Ti(IV) complex increases mitochondrial reactive oxygen species levels in relation with hypoxia and endoplasmic-reticulum stress: A distinct non DNA-related mechanism

PhenolaTi is a promising Ti(IV) anticancer complex, with high stability and cytotoxicity, without notable toxic side-effects. Its cellular mechanism was proposed to relate to ER stress. Herein, we investigated the downstream effects of this mode of action in two cancer cell lines: ovarian carcinoma A2780 and cervical adenocarcinoma HeLa. First, although Ti(IV) is a non-redox metal, the formation of mitochondrial reactive oxygen species (ROS) was detected with live-cell imaging. Then, we inspected the effect of the mitochondrial ROS on cytotoxicity, using two methods: (a) addition of compounds that either elevate or reduce the mitochondrial glutathione concentration, thus affecting the oxidative state of the cells; and (b) scavenging mitochondrial ROS. Unlike the results observed for cisplatin, neither method influenced the cytotoxicity of phenolaTi, implying that ROS formation was a mere side effect of its activity. Additionally, live cell imaging displayed the hypoxia induced by phenolaTi, which can be associated with ROS formation. Overall, the results support the notion that ER-stress is the main cellular mechanism of phenolaTi, leading to hypoxia and mitochondrial ROS. The distinct mechanism of phenolaTi, which is different from that of cisplatin, combined with its stability and favorable anticancer properties, altogether make it a strong chemotherapeutic drug candidate.