Titanium Center Research Articles

Stabilization of Ethane‐like Dianionic Diborane(6) in Monometallic Titanium Complexes and its Subsequent B(sp3)‐B(sp3) Bond Cleavage

Treatment of [Cp*TiCl3] with [LiBH4∙THF] followed by thermolysis with [Ph2E2] (E = S or Se) resulted in the formation of classical diborane(6) complexes, [(Cp*Ti)(η4‐B2H4LL')] (L = C6H4E; L' = C6H5E; 1a: E = S, 1b: E = Se), stabilized at titanium template. To the best of our knowledge, they are the first examples of mono‐metallic classical diborane(6) complexes. The bonding analysis and theoretical studies suggest that the stabilization of these diborane(6) species is due to the presence of four bridging ligands in ĸ4‐fashion, where two of them are phenyl thiolates/selenolates that provide more electrons to the electron‐deficient titanium center. Reactions of these diborane(6) species with [M(CO)5∙THF] (M = Mo, W) led to the cleavage of electron‐precise B(sp3)‐B(sp3) bond that yielded ĸ3‐hydridoborato complexes [(Cp*Ti)(ĸ3‐BH3R)(μ‐EPh)2{M(CO)4}] (2a‐c: R = H, 3a‐c: R = Ph). In an attempt to isolate the Te‐analogue of 1a‐b, a similar reaction was performed; however, the complex was too unstable to be isolated. Interestingly, the treatment of this unstable intermediate with [W(CO)5∙THF] yielded [(Cp*Ti)(ĸ3‐BH3R)(μ‐TePh)2{W(CO)4}] (2d: R = H, 3d: R = Ph) that are analogues of 2a‐c and 3a‐c, respectively. Formation of these species provide indirect evidence for existence of unstable [(Cp*Ti)(η4‐B2H4LL')] (L = C6H4Te; L' = C6H5Te; 1c).

Stabilization of Ethane-like Dianionic Diborane(6) in Monometallic Titanium Complexes and its Subsequent B(sp3)-B(sp3) Bond Cleavage.

Treatment of [Cp*TiCl3] with [LiBH4∙THF] followed by thermolysis with [Ph2E2] (E = S or Se) resulted in the formation of classical diborane(6) complexes, [(Cp*Ti)(η4-B2H4LL')] (L = C6H4E; L' = C6H5E; 1a: E = S, 1b: E = Se), stabilized at titanium template. To the best of our knowledge, they are the first examples of mono-metallic classical diborane(6) complexes. The bonding analysis and theoretical studies suggest that the stabilization of these diborane(6) species is due to the presence of four bridging ligands in ĸ4-fashion, where two of them are phenyl thiolates/selenolates that provide more electrons to the electron-deficient titanium center. Reactions of these diborane(6) species with [M(CO)5∙THF] (M = Mo, W) led to the cleavage of electron-precise B(sp3)-B(sp3) bond that yielded ĸ3-hydridoborato complexes [(Cp*Ti)(ĸ3-BH3R)(μ-EPh)2{M(CO)4}] (2a-c: R = H, 3a-c: R = Ph). In an attempt to isolate the Te-analogue of 1a-b, a similar reaction was performed; however, the complex was too unstable to be isolated. Interestingly, the treatment of this unstable intermediate with [W(CO)5∙THF] yielded [(Cp*Ti)(ĸ3-BH3R)(μ-TePh)2{W(CO)4}] (2d: R = H, 3d: R = Ph) that are analogues of 2a-c and 3a-c, respectively. Formation of these species provide indirect evidence forexistence of unstable [(Cp*Ti)(η4-B2H4LL')] (L = C6H4Te; L' = C6H5Te; 1c).

Exploring Dinuclear Titanium Complexes in Titanium(III) Catalysis

AbstractThe synthesis of one achiral and two chiral propylene‐bridged dititanocenes and their evaluation as catalysts in titanium(III) catalyzed ketone‐nitrile coupling reactions are reported. A reaction progress kinetics analysis of the cross‐coupling between acetophenone and benzyl cyanide reveals that, using a dinuclear titanocene catalyst, the order in catalyst is reduced from two to one in comparison to a mononuclear catalyst. Although the obtained coupling yields and enantioselectivities did not reach the results obtained with the latter, these examples constitute a proof of concept for the templated C─C coupling through coordination of ketone and nitrile to the two tethered titanium centers of a dinuclear catalyst.

Titanium (IV) μ-Oxo Complex Supported by Phenoxyimine Ligand: Synthesis, Crystal Structure Characterisation, DFT and Molecular Docking Studies

Background: Most of the transition elements in the 3d series (first row transition metals) have been discovered to be extremely significant and practical in biological systems. Naturally, many of the enzymes that are present in the human body system act as catalysts for biological processes and are made of coordination compounds or complexes. Objective: The complex has been characterised by various spectroscopic and analytic techniques. A suitable crystal analysed by X-ray diffraction establishes the formation of a stable binuclear µ-oxo-complex with a hexacoordinate titanium centre. Methods: A new crystalline complex [Ti{La}] has been synthesised in the reaction of titanium butoxide with a phenoxyimine ligand in a 1:1 stoichiometry in toluene at room temperature under a nitrogen atmosphere. The newly synthesised Ti complex has undergone density functional theory and docking study. Results: The crystal shows a monoclinic system with space group C 1 2/c 1. X-ray crystal structure analysis reveals that this complex has a rhomboidal Ti-O-Ti core and exhibits a C2 symmetric conformation with distorted octahedral geometry. Density Functional Theory (DFT) calculations giving insights into the frontier orbitals and mulliken charge analysis, which showed good correlation with the experimental findings. Additionally, in silico molecular docking of ligand and complex was carried out against the HER2 inhibitor kinase. Conclusion: This complex exhibits a higher binding energy of ΔGb = -19.7 kcal/mol with the active pocket of HER2 (PDB:7JXH) than the ligand ΔGb = -8.5 kcal/mol.

Vinyl-addition copolymerization of norbornene and 1-octene catalyzed by a non-bridged half-titanocene with a tetrazole-phenoxy ligand

A catalyst system comprising Cp*TiCl2(OPhTz) (Cp* = C5Me5, OPhTz = tetrazole-mono-ortho-substituted phenoxy anion), iBu3Al, and [Ph3C][B(C6F5)4] is employed in the vinyl-addition copolymerization of norbornene (NB) and 1-octene (OT) to understand the catalytic effects of the N-donor tetrazole substituent. Copolymerization is accompanied by significant β-hydride elimination, producing poly(norbornene-co-1-octene) (P(NB-co-OT)) with low yield and molecular weight. Although the incorporation of OT into the copolymer is less than expected, competitive incorporation of the two monomers is observed. Increasing the mole fraction of OT in the feed reduces both the yield and molecular weight of the copolymer. Spectroscopic analysis reveals that the catalyst system yields P(NB-co-OT)s that are terminated prior to complete monomer conversion, along with non-isolated cooligomers and OT-derived isomers. The cationic titanium(IV) center stabilized by the N-donor tetrazole substituent facilitates the highly regioselective 2,1-insertion of OT. This slows subsequent monomer insertion, thereby promoting β-hydride elimination.

Coordination-Induced Radical Generation: Selective Hydrogen Atom Abstraction via Controlled Ti-C σ-Bond Homolysis.

A method for the generation of transient alkyl radicals via homolytic Ti-C bond cleavage was developed by employing a tailor-made organotitanium half-cage complex. In contrast to established metal-mediated radical initiation protocols via thermal or photochemical M-C σ-bond homolysis, radical formation is triggered solely by coordination of a solvent molecule (thf) to a titanium(IV) center. During the reaction, the nonstabilized alkyl radical is formed along with a persistent titanium(III) metalloradical, thus taming the former transient radical (persistent radical effect). Radical coupling and hydrogen atom abstraction (HAT) reactions have been explored not only experimentally but also computationally and by means of kinetic analysis. Exploiting these findings led to the development of selective HAT transformations, for example, with 9,10-dihydroanthracene. Deuterium labeling studies using selectively deuterated alkyls and 9,10-dihydroanthracene-d4 confirmed a radical pathway, which was underpinned by developing a radical-radical cross-coupling reaction for transferring the alkyl radical to a stable Sn-centered radical. To set the stage for an application in organic synthesis, a 5-endo-trig radical cyclization based on our methodology was established, and a dihydroxylated sesquiterpene was thus prepared in high diastereomeric excess.

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.

Dimethylformamide Impurities as Propylene Polymerization Inhibitor.

This research study examined how the use of dimethylformamide (DMF) as an inhibitor affects the propylene polymerization process when using a Ziegler-Natta catalyst. Several experiments were carried out using TiCl4/MgCl2 as a catalyst, aluminum trialkyl as a cocatalyst, and different amounts of DMF. Then, we analyzed how DMF influences other aspects of the process, such as catalyst activity, molecular weight, and the number of branches in the polymer chains obtained, using experimental and computational methods. The results revealed that as the DMF/Ti ratio increases, the catalyst activity decreases. From a concentration of 5.11 ppm of DMF, a decrease in catalyst activity was observed, ranging from 45 TM/Kg to 44 TM/Kg. When the DMF concentration was increased to 40.23 ppm, the catalyst activity decreased to 43 TM/Kg, and with 75.32 ppm, it dropped even further to 39 TM/Kg. The highest concentration of DMF evaluated, 89.92 ppm, resulted in a catalyst productivity of 36.5 TM/Kg and lost productivity of 22%. In addition, significant changes in the polymer's melt flow index (MFI) were noted as the DMF concentration increased. When 89.92 ppm of DMF was added, the MFI loss was 75%, indicating a higher flowability of the polymer. In this study, it was found that dimethylformamide (DMF) exhibits a strong affinity for the titanium center of a Ziegler-Natta (ZN) catalyst, with an adsorption energy (Ead) of approximately -46.157 kcal/mol, indicating a robust interaction. This affinity is significantly higher compared to propylene, which has an Ead of approximately -5.2 kcal/mol. The study also revealed that the energy gap between the highest occupied molecular orbital (HOMO) of DMF and the lowest unoccupied molecular orbital (SOMO) of the Ziegler-Natta (ZN) catalyst is energetically favorable, with a value of approximately 0.311 eV.

Nano-Cavities within Nano-Zeolites: The Influencing Factors of the Fabricating Process on Their Catalytic Activities.

Titanium silicalite-1 (TS-1) is a milestone heterogeneous catalyst with single-atom tetrahedral titanium incorporated into silica framework for green oxidation reactions. Although TS-1 catalysts have been industrialized, the strategy of direct hydrothermal synthesis usually produces catalysts with low catalytic activities, which has still puzzled academic and industrial scientists. Post-treatment processes were widely chosen and were proven to be an essential process for the stable production of the high-activity zeolites with hollow structures. However, the reasons why post-treatment processes could improve catalytic activity are still not clear enough. Here, high-performance hollow TS-1 zeolites with nano-sized crystals and nano-sized cavities were synthesized via post-treatment of direct-synthesis nano-sized TS-1 zeolites. The influencing factors of the fabricating processes on their catalytic activities were investigated in detail, including the content of alkali metal ions, the state of titanium centers, hydrophilic/hydrophobic properties, and accessibility of micropores. The post-treatment processes could effectively solve these adverse effects to improve catalytic activity and to stabilize production. These findings contribute to the stable preparation of high-performance TS-1 catalysts in both factories and laboratories.

Monocyclopentadienyltitanium(III) Complexes with Hydridoborato Ligands

The synthesis, properties, and reactivity of monocyclopentadienyltitanium(III) complexes stabilized by hydridoborato (BH3R)− ligands are reported. The reactions of the titanium(IV) trichlorides [Ti(η5-C5H5–nMen)Cl3] with excess LiBH3R (R = H, Me) afford dimeric [{Ti(η5-C5H5–nMen)(BH4)(μ-BH4)}2] (n = 5 (1), 4 (2), 0 (3)) or monomeric [Ti(η5-C5Me5)(BH3Me)2] (4) titanium(III) derivatives. Compound 3 is a thermally unstable oil and decomposes at room temperature forming a mixed-valence TiII/TiIII tetrametallic species [{Ti(η5-C5H5)(BH4)}2{(μ3-B2H6)Ti(η5-C5H5)}2] (5) with dianionic diborane(6) ligands in a rare μ3-κ2:κ2:κ2-B2H6 coordination mode. Density functional theory (DFT) calculations for 5 agree with a triplet ground state with two inner titanium(II) atoms bonded by a single bond and two outer titanium(III) centers. In contrast to 3, the monomeric tetrahydrofuran adduct derivative [Ti(η5-C5H5)(BH4)2(thf)] (6) is a stable solid. Dimeric 1–3 react with 2,6-lutidinium salts (LutH)X (X = BPh4, OSO2CF3) to afford ion pairs, [Ti(η5-C5H5–nMen)(BH4)L2](BPh4) (L = thf, n = 5 (7), 4 (8), 0 (9); L = py, n = 5 (10)), or molecular aggregates, [{Ti(η5-C5Me5)(BH4)(μ-O2SOCF3)}2] (11) and [{Ti(η5-C5H5–nMen)(μ-O2SOCF3)2}x] (n = 5, x = 3 (12); n = 4, x = 4 (13)), via formation of H2 and (Lut)BH3. Diamagnetic titanium(II) derivatives [{Ti(η5-C5Me5)(μ-H)}2{(μ-H)2Al(BH3R)(thf)}2] (R = H (14), Me (15)) were isolated in reactions of complexes 1 and 4 with LiAlH4 in tetrahydrofuran.

Development of ProPhenol/Ti(IV) Catalyst for Asymmetric Hydroxylative Dearomatization of Naphthols

By development of ProPhenol/Ti(IV) catalysts, a catalytic enantioselective hydroxylative dearomatization of naphthols is achieved by using TBHP as a simple oxidative reagent. The side coordinative chain equipped on the C1-position of β-naphthols plays an important role for initiating this asymmetric hydroxylative reaction, which might be a result of the proper cocoordination effects to the titanium center in the catalyst. A reasonable catalytic cycle is proposed, the catalytic system is applied to a reasonable range of this type of phenolic compound, and related concise transformations are carried out.

Targeted construction of a three-dimensional metal covalent organic framework with spn topology for photocatalytic hydrogen peroxide production

A 3D metal covalent organic framework (TiCOF-spn) with unreported spn topology was synthesized for photocatalytic H 2 O 2 production. This work expands the topology of the 3D COFs family and pioneers the application of metal-containing COFs in solar energy conversion. • Metal-containing units overcome the obstacle of limited polyhedral organic molecular for 3D COFs. • A 3D metal covalent organic framework (TiCOF-spn) possesses unreported spn topology. • TiCOF-spn pioneers the application of solar energy conversion with H 2 O 2 photocatalysis. To enrich the topology of three-dimensional covalent organic frameworks (3D COFs) is an appealing challenge. Till now, only 20 types of topologies have been achieved in 3D COFs because of the limited polyhedral building blocks. Herein, we report the first 3D titanium-based COF with spn topology (TiCOF-spn) through [6 + 3] imine condensation of a Ti(IV) complex with six aldehyde groups positioned in a trigonal antiprismatic arrangement and a planar triazine-based amine connector. Interestingly, TiCOF-spn contains two kinds of pores, that is, the linking of the tetrahedral cages by sharing vertices forms the truncated tetrahedral cages. By integrating the crystalline porous framework, photoactive titanium center and triazine component, TiCOF-spn shows strong visible light absorption and efficient photocatalytic activity for producing H 2 O 2 (489.94 μmol g −1 h −1 ). This work expands the topology of the 3D COFs family and pioneers the application of metal-containing COFs in solar energy conversion.

Going Up the Ladder: Stacking Four 4,4'-Bipyridine Moieties within a Ti(IV)-Based Tetranuclear Architecture.

Biphenol-based ligands have proven their ability to bind titanium(IV) centers and generate sophisticated self-assembled structures in which auxiliary nitrogen ligands often complete the coordination sphere of the metal and improve stability. Here, a central 4,4'-bipyridine, which acts as both a spacer and a source of monodentate nitrogen to complete the coordination sphere of the Ti(IV) complex, was incorporated within two bis-2,2'-biphenol strands, 3H4 and 4H4. Both proligands possess structural features that are well adapted to form self-assembled structures built from titanium-oxygen-nitrogen units; however, their different degrees of torsional freedom strongly influenced the nuclearity of the complexes formed. The presence of a phenyl spacer between the bipyridine and the biphenol moieties of 3H4 provided enough flexibility for the ligand to wrap around one titanium(IV) center to form a mononuclear complex Ti(3)(DMF)2 in the presence of dimethylformamide (DMF). Assembly of the more rigid ligand 4H4 with Ti(OiPr)4 afforded a tetranuclear complex Ti4(4)2(4H)2(OEt)2 containing four stacked 4,4'-bipyridine units as shown by the X-ray structure of the complex. Density functional theory studies suggested that the assembly of this tetrametallic complex involves a dimetallic intermediate with TiO6 nodes that is converted to the thermodynamically stable tetranuclear complex with two TiO6 nodes and two TiO5N units with enhanced covalent character.

Effects of Different Concentrations of Arsine on the Synthesis and Final Properties of Polypropylene.

This article studies the effects of arsine on the synthesis and thermal degradation of 4 samples of virgin polypropylene (PP-virgin) and proposes reaction mechanisms that allow understanding of its behaviour. Different points are monitored during the polypropylene synthesis to perform TGA, DSC, FT-IR, RDX, and MFI analyses later. The content of AsH3 in polypropylene varies between 0.05 and 4.73 ppm, and of arsenic in virgin PP residues between 0.001 and 4.32 ppm for PP0 and PP10, increasing in fluidity index from 3.0 to 24.51. The origin of thermo-oxidative degradation is explained by the reaction mechanisms of the Molecule AsH3 with the active titanium center of the ZN catalyst and the subsequent oxidation to form radical complexes. OO-AsH-TiCl4-MgCl2 and (OO-as-OO)2 -TiCl4-MgCl2, which, by radical reactions, give rise to the formation of functional groups aldehyde, ketone, alcohol, carboxylic acid, CO, CO2, PP-Polyol, PP-Polyether, and PP-Isopropylethers. These species caused the TG and DTG curves to increase degradation peaks in pp samples.

A Guide to Low‐Valent Titanocene Complexes as Tunable Single‐Electron Transfer Catalysts for Applications in Organic Chemistry

AbstractLow‐valent titanocene catalysts are a versatile tool for organic synthesis. They promote inter‐ and intramolecular reactions ranging from homolytic bond cleavages to reductive umpolung reactions to additions and cyclizations in single electron steps. These reactions heavily depend on the redox potential of an in situ formed titanium(III) center, which can be adjusted by the choice of appropriate ligands. We herein review various chiral and achiral ligand‐modified titanocene catalysts and their reduction potentials Ep/2 obtained via cyclic voltammetry. The latter are found to correlate with the Hammett parameters σp of the cyclopentadienyl substituents and to the pKa values of the corresponding acids of the Ti−X ligands. For selected examples, we further discuss how the adjustment of the redox properties through modifications of the titanocene ligands can lead to greatly improved reaction outcomes in titanium(III) catalyzed single‐electron transfer reactions.

Homogeneous {Ti2Ni} Heterotrinuclear Catalyst for Ethylene Polymerization and Copolymerization

We synthesized and spectroscopically characterized a new heterotrimetallic {Ti2Ni} ethylene (co)polymerization precatalyst containing one (α-diimine)NiBr2 and two (phenoxy-imine)TiCl4 scaffolds. Its calculated structure was investigated at the DFT B3LYP/LACVP** level. Our calculations showed that the titanium(IV) centers were in a slightly distorted trigonal bipyramidal environment, and the average Ti···Ni distance was 8.76 Å. The precatalyst was used for synthesizing polyethylene and ethylene copolymers. The results of GPC analyses showed that the obtained polyethylenes had the desired bimodal molecular weight distributions. The FTIR spectra revealed that polydispersity decreased as the vinyl end-group content increased. These results suggested that high mechanical resistance can increase the mechanical energy needed for processing the material. All 13C NMR signals were assigned to short-chain branches with specific spatial arrangements along the polymer backbone. The chain walking mechanism of branch formation controls the spacing and conformational arrangements between these short chains.

Structural Modification Engineering of Si Nanoparticles by MIL‐125 for High‐performance Lithium‐ion Storage

AbstractSi‐based anode electrodes stand out for its excellent capacity among the numerous anode electrodes for lithium‐ion batteries. However, there is still a problem that the volume expansion from the alloying reaction of Li and Si often leads to structural collapse and rapidly capacity degradation. Here, Si nanoparticles (Si NPs) are coated via metal‐organic frameworks (MOFs) derived skeleton to buffer its volume expansion, thereby improving electrochemical properties. Scanning electron microscopy was applied to revealed morphology and structure of the composite material. The results demonstrate that the structure of the prepared composite is Si NPs encapsulated in the unique carbon skeleton. The as‐prepared Si@MIL‐125‐500 exhibits excellent electrochemical performances with an excellent reversible capacity of 304.3 mAh g−1 at 5 A g−1 even after 400 cycles. In addition, the initial coulombic efficiency (ICE) reached up to 86 %. The improved electrochemical performance could be attributed to the distinctive structure of the carbon coated Si NPs and stable titanium(IV) center site, which has improved the electrical conductivity and cycling stability of Si NPs. Moreover, the empty space inside the MOF's carbon skeleton can release the volume strain of Si during electrochemical process. There is an improvement of electrochemical properties for LIBs due to Si NPs restricted in MIL‐125.

Titanium Complexes of Salicylbenzoxazole and Salicylbenzothiazole Ligands for the Ring-Opening Polymerization of ε-Caprolactone and Substituted ε-Caprolactones and Their Copolymerizations.

Two series of titanium complexes, including salicylbenzoxazole titanium complexes (1-4) and salicylbenzothiazole titanium complexes (5-8), were successfully synthesized and characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction crystallography (for 2 and 5). The 1H NMR spectra of complexes 7 and 8 reveal fluxional behavior in solution at room temperature, and the activation parameters were determined by lineshape analysis of variable-temperature (VT) NMR spectra in toluene-d8: for 7, ΔH⧧ = 73.0 ± 1.8 kJ mol-1, ΔS⧧ = 22.1 ± 5.5 J mol-1 K-1; for 8, ΔH⧧ = 73.7 ± 1.2 kJ mol-1, ΔS⧧ = 20.3 ± 3.8 J mol-1 K-1. The positive values of ΔS⧧ suggested that the isomerization occurred via a dissociative mechanism. All complexes were active initiators for the ring-opening polymerization of ε-caprolactone (ε-CL) and three substituted ε-CLs: γ-methyl-ε-caprolactone (γMeCL), γ-ethyl-ε-caprolactone (γEtCL), and γ-phenyl-ε-caprolactone (γPhCL). Of all complexes, complex 5 was found to be the most active initiator in this study. The copolymerizations between ε-CL and three substituted ε-CLs produced completely random copolymers. The polymerization was proposed to proceed via a dissociative coordination-insertion mechanism. The catalytic activity of the salicylbenzoxazole titanium complex was lower than that of its closely related salicylbenzothiazole titanium congener. Additionally, DFT calculations unveiled that the ligand decoordination step and the less steric congestion at the titanium center in the salicylbenzothiazole titanium complexes were the key factors in enhancing the catalytic rate.

Ti(IV)-Exchanged Nano-ZIF-8 and Nano-ZIF-67 for Enhanced Photocatalytic Oxidation of Hydroquinone

The metal centres of nano-zeolitic imidazolate framework-8(Zinc) and 67(Cobalt) [nZIF-8(Zn) and nZIF-67(Co)] were partially exchanged with titanium (Ti) centres to form bimetallic nZIF-8(Zn/Ti) (52% Ti4+) and nZIF-67(Co/Ti) (38% Ti4+) respectively, for enhanced photocatalytic performance. A morphological and structural analysis by scanning electron microscopy, energy dispersive spectroscopy (EDS)-mapping and powder X-ray diffraction showed that the particle size, distribution, and the structural integrity of the Sodalite frameworks of the parent ZIFs were retained during the exchange process to form the new bimetallic Ti-ZIFs. Fourier transform infrared spectroscopy confirmed that no additional chemical bonds were formed during the process. X-ray photoelectron spectroscopy binding energies confirmed the preservation of the Zn(II), Co(II) and Ti(IV) oxidation states, as well as the Ti-content, consistent with inductively coupled plasma-optical emission spectrometry and EDS measurements. The Ti-exchanged ZIFs showed higher activity during the photocatalytic oxidation of hydroquinone in comparison with their parent ZIFs. Their kinetic rates were nearly five times faster than those of the parent ZIFs, with the first-order rate constants k = 0.189 min−1 for nZIF-8(Zn/Ti) and k = 0.139 min−1 for nZIF-67(Co/Ti). These catalysts are efficient, stable, and reusable for three photocatalytic cycles without a significant loss of catalytic activity.

Latest News: Reactions of Group 4 Bis(trimethylsilyl)acetylene Metallocene Complexes and Applications of the Obtained Products

Recently published reactions of group 4 metallocene bis(trimethylsilyl)acetylene (btmsa) complexes from the last two years are reviewed. Complexes like Cp’2Ti(η2‐Me3SiC2SiMe3) and Cp2Zr(py)(η2‐Me3SiC2SiMe3) with Cp’ as Cp (cyclopentadienyl) and Cp* (pentamethylcyclopentadienyl) have been considered (py=pyridine). These complexes can liberate a reactive low‐valent titanium or zirconium center by dissociation of the ligands and act as ‘‘masked’’ MII complexes (M=Ti, Zr). They represent excellent sources for the clean generation of the reactive coordinatively and electronically unsaturated complex fragments [Cp’2M]. This is the reason why they were used for many synthetic and catalytic reactions during the last years. As an update to several review articles on this topic, this contribution provides an update with recent examples of preparative organometallic and organic chemistry of these complexes, acting as reagents for a wide range of coordinating and coupling reactions. In addition, applications and investigations concerning reaction products derived from this chemistry are mentioned, too.