Site‐Selective Ligand Exchange on a Heteroleptic TiIV Complex Towards Stepwise Multicomponent Self‐Assembly

A series of heteroleptic [Ti 1 ₂X]^? complexes have been selectively constructed from a mixture of Ti^IV ions, a pyridyl catechol ligand (H₂ 1 ; H₂ 1 =4‐(3‐pyridyl)catechol), and various bidentate ligands (HX) in the presence of a weak base, in addition to a previously reported [Ti 1 ₂(acac)]^? (acac=acetylacetonate) complex. Comparative studies of these Ti^IV complexes revealed that [Ti 1 ₂(trop)]^? (trop=tropolonate) is much more stable than the [Ti 1 ₂(acac)]^? complex, which allows the replacement of acac with trop on the [Ti 1 ₂(acac)]^? complex. This Ti^IV‐centered site‐selective ligand exchange reaction also takes place on a heteronuclear Pd^II? Ti^IV ring complex with the preservation of the Pd^II‐centered coordination structures. Intra‐ and intermolecular linking between two Ti^IV centers with a flexible or a rigid bis‐tropolone bridging ligand provided a tetranuclear and an octanuclear Pd^II? Ti^IV complex, respectively. These higher‐order structures could be efficiently constructed only through a stepwise synthetic route.     

Methoxokomplexe drei-, vier- und fünfwertiger Zentralatome

The complex formation with CH₃O^? of As^III, Sb^III, Ge^IV, Nb^IV, Se^IV, Te^IV, Ti^IV, Sn^IV and Mo^V has been investigated in absolute methanolic solutions containing (CH₃)₄NCl, LiCl, or Lithiumtosylate (μ = 1; 20.0°) by means of pH-titrations. The relations between the stoichiometry of the reactions and the shape of the buffer regions, as well as the concentration-dependance of these buffer regions are discussed.     

SiIV Incorporation into a [28]Hexaphyrin That Triggered Formation of Möbius Aromatic Molecules

Incorporation of Si^IV into an expanded porphyrin has been achieved for the first time. Treatment of [28]hexaphyrin 1 with CH₃SiCl₃ and N,N‐diisopropylethylamine gave Si^IV complex 2 and its N‐fused product 4 that both have Möbius aromatic nature. In both complexes, the coordinated Si atom is satisfied in a typical trigonal bipyramidal coordination. Si^IV incorporation induces conformational rigidification and redshifted absorption profiles due to σ–π conjugation between the Si atom and hexaphyrin macrocycle. Tamao–Fleming oxidation of 2 with H₂O₂ gave β‐hydroxy [28]hexaphyrin 5 , which exists as a ruffled rectangular shape in the solid state, yet it has been revealed to exist predominantly as a twisted Möbius aromatic conformer in CH₂Cl₂.     

Synthesen,IR- und 15N-Kernresonanzspektren isotopen-markierter Nitridokomplexe des Wolframs

Isothermal Section at 1273 K in the System Ti? Si? O The isothermal section at 1273 K of the system Ti? Si? O has been investigated by means of phase analysis in quenched samples as well as by the investigation of the phase sequence in chemical vapour transport experiments. In equilibrium with SiO₂ only TiSi₂, TiSi, and Ti₅Si₃(O), respectively, can coexist as Si-containing compounds. Only Ti₅Si₃(O) can coexist with titanium oxides (Ti₂O₃ or TiO, respectively). Ti₅Si₄ is stable only if oxygen is absent.     

Asymmetric trimethylsilylcyanation of aldehydes catalyzed by chiral salen TiIV complexes with theC 1 symmetry

Asymmetric trimethylsilylcyanation of a number of aromatic and aliphatic aldehydes catalyzed by chiral Ti^IV complexes preparedin situ from Ti(OPrⁱ)₄ and (1S)-[N,N′-bis(2′-hydroxy-3′-tert-butylbenzylidene)]-1,2-diaminoalkanes gives products with (S)-absolute configurations. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2040–2042, November, 1997.     

Cover Feature: How Many O-Donor Groups in Enterobactin Does It Take to Bind a Metal Cation? (Chem. Eur. J. 28/2019)

The E. coli siderophore enterobactin, the strongest Fe^III chelator known to date, forms hexacoordinate complexes with Si^IV, Ge^IV, and Ti^IV. Synthetic protocols have been developed to prepare non-symmetric enterobactin analogues with varying denticities. Various benzoic acid residues were coupled to the macrocyclic lactone to afford a diverse library of ligands. These enterobactin analogues were bound to Si^IV, Ge^IV, and Ti^IV, and the complexes were investigated through experimental and computational techniques. The binding behavior of the synthesized chelators enabled assessment of the contribution of each of the phenolic hydroxy groups in enterobactin to metal-ion complexation. It was found that at least four O-donors are needed for enterobactin derivatives to act as metal binders. Density functional theory calculations indicate that the strong binding behavior of enterobactin can be ascribed to a diminished translational entropy penalty, a common feature of the chelate effect, coupled with the structural arrangement of the three catechol moieties, which allows the triseryl base to be installed without distorting the preferred local metal-binding geometry of the catecholate ligands.     

Crystal structures of lazulite-type oxidephosphates TiTi3O3(PO4)3 and M4Ti27O24(PO4)24 (M=Ti, Cr, Fe)

Single crystals of the oxidephosphates Ti^IIITi^IV₃O₃(PO₄)₃ (black), Cr^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (red-brown, transparent), and Fe^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (brown) with edge-lengths up to 0.3 mm were grown by chemical vapour transport. The crystal structures of these orthorhombic members (space group F2dd ) of the lazulite/lipscombite structure family were refined from single-crystal data [Ti^IIITi^IV₃O₃(PO₄)₃: Z=24, a=7.3261(9) Å, b=22.166(5) Å, c=39.239(8) Å, R₁=0.029, wR₂=0.084, 6055 independent reflections, 301 variables; Cr^III₄Ti^IV₂₇O₂₄(PO₄)₂₄: Z=1, a=7.419(3) Å, b=21.640(5) Å, c=13.057(4) Å, R₁=0.037, wR₂=0.097, 1524 independent reflections, 111 variables; Fe^III₄Ti^IV₂₇O₂₄(PO₄)₂₄: Z=1, a=7.4001(9) Å, b=21.7503(2) Å, c=12.775(3) Å, R₁=0.049, wR₂=0.140, 1240 independent reflections, 112 variables). For Ti^IIITi^IVO₃(PO₄)₃ a well-ordered structure built from dimers [Ti^III,IV₂O₉] and [Ti^IV,IV₂O₉] and phosphate tetrahedra is found. The metal sites in the crystal structures of Cr₄Ti₂₇O₂₄(PO₄)₂₄ and Fe₄Ti₂₇O₂₄(PO₄)₂₄, consisting of dimers [M^IIITi^IVO₉] and [Ti^IV,IV₂O₉], monomeric [Ti^IVO₆] octahedra, and phosphate tetrahedra, are heavily disordered. Site disorder, leading to partial occupancy of all octahedral voids of the parent lipscombite/lazulite structure, as well as splitting of the metal positions is observed. According to Guinier photographs Ti^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (a=7.418(2) Å, b=21.933(6) Å, c=12.948(7) Å) is isotypic to the oxidephosphates M^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (M^III: Cr, Fe). The UV/vis spectrum of Cr₄Ti₂₇O₂₄(PO₄)₂₄ reveals a rather small ligand-field splitting Δ_o=14,370 cm⁻¹ and a very low nephelauxetic ratio β=0.72 for the chromophores [Cr^IIIO₆] within the dimers [Cr^IIITi^IVO₉].     

Synthesis and Structural Characterization of Hexacoordinate Silicon,Germanium, and Titanium Complexes of the E. coli Siderophore Enterobactin

The E. coli siderophore enterobactin, one of the strongest Fe^III chelators known to date, is also capable of binding Si^IV under physiological conditions. We report on the synthesis and structural characterization of the tris(catecholate) Si^IV–enterobactin complex and its Ge^IV and Ti^IV analogues. Comparative structural analysis, supported by quantum‐chemical calculations, reveals the correlation between the ionic radius and the structural changes in enterobactin upon complexation.     

Bemerkungen zum Gebrauch des Silber-Reduktors

Zusammenfassung Es wurde das Verhalten des Ti⁴⁺/Ti³⁺-Systems gegenüber dem Silberreduktor untersucht und festgestellt, daß Ti^IV bei 85° C in dem Medium von 7,3 n Salzsäure und 3,2 n Essigsäure am Silberreduktor quantitativ zu Ti^III reduziert wird. Dieses Ergebnis ist darauf zurückzuführen, daß die Essigsäure, die mit den Ti-Ionen einen stabilen Komplex bildet, das Redoxpotential des Ti⁴⁺/Ti³⁺ Systems erhöht und damit die quantitative Reduktion fördert. Die Reduktion wird durch Eisen in zehnfachem Überschuß sowie durch Co²⁺, Ni²⁺, Mn²⁺, Cr³⁺ und PO₄ ^3– in fünffachem Überschuß nicht gestört. In Anwesenheit von Mo^VI, U^VI, W^VI und Fluoriden ist die Bestimmung nicht durchführbar. Die Reduktionsreaktion zur Titanbestimmung wurde im Ferrotitan angewendet. Das reduzierte Ti^III wurde mit einer Fe₂(SO₄)₃-Maßlösung potentiometrisch titriert. Die Genauigkeit der Bestimmung beträgt± 0,75%.     

Schwingungsspektren einiger Methylmethoxydisilane und des Hexamethoxydisilans

Zusammenfassung Die IR- und Raman-Spektren der MethylmethoxydisilaneI–IV und von Si₂(Ome)₆ [me=CH₃] wurden aufgenommen und zugeordnet. Deuteriumsubstitution der Methoxygruppen dient zur Erkennung von Schwingungskopplungen und liefert Zusatzinformationen für eine Normalkoordinatenanalyse an Si₂(Ome)₆. Die SiSi-Valenzkraftkonstante nimmt ausgehend von Si₂ me ₆ mit steigender Anzahl dermeO-Gruppen zu und erreicht in Si₂(Ome)₆ einen Wert von 2,25 mdyn/Å.

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Vibrational spectra of some methylmethoxydisilanes and of hexamethoxydisilane

The infrared and Raman spectra of the methylmethoxydisilanesI–IV and of Si₂(Ome)₆ [me=CH₃] were reported and assigned. CD₃O-substitution elucidated vibrational couplings and supplied additional data for a normal coordinate analysis of Si₂(Ome)₆. The SiSi-stretching force constant increases with increasing number ofmeO-substituents and amounts to 2.25 mdyn/Å in Si₂(Ome)₆.

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Herrn Prof. Dr. E. Ziegler zum 60. Geburtstag gewidmet.     

A Flexible Photoactive Titanium Metal–Organic Framework Based on a [TiIV3(μ3‐O)(O)2(COO)6] Cluster

The synthesis of titanium–carboxylate metal–organic frameworks (MOFs) is hampered by the high reactivity of the commonly employed alkoxide precursors. Herein, we present an innovative approach to titanium‐based MOFs by the use of titanocene dichloride to synthesize COK‐69, the first breathing Ti MOF, which is built up from trans‐1,4‐cyclohexanedicarboxylate linkers and an unprecedented [Ti^IV₃(μ₃‐O)(O)₂(COO)₆] cluster. The photoactive properties of COK‐69 were investigated in depth by proton‐coupled electron‐transfer experiments, which revealed that up to one Ti^IV center per cluster can be photoreduced to Ti^III while preserving the structural integrity of the framework. The electronic structure of COK‐69 was determined by molecular modeling, and a band gap of 3.77 eV was found.     

Stibene epoxidation with t-butyl hydroperoxide and hydrogen peroxide catalyzed by transition metal substituted heteropolytungstates

Tetra-n-butylammonium salts of transition metal-substituted heteropolytungstates, PW₁₁MO ₃₉ ^n– , catalyze the epoxidation of stilbenes by t-butyl hydroperoxide (M=Co^II, Mn^II, Cu^II, Ti^IV, Ru^IV, V^V, Nb^V) and hydrogen peroxide (M=Zr^IV) in acetonitrile. Epoxidation of cis-stilbene is non-stereospecific.     

Synthetic studies of organodi-π-cyclopentadienyl- titanium (III) derivatives

Two synthetic routes to compounds of the type π-Cp₂Ti^IIIR (R=CH₃, CH₂Si(CH₃)₃, C₆F₅) have been investigated: (a) chemical reduction of π-Cp₂Ti^IV(R)Cl by zinc or aluminum metal in tetrahydrofuran, and (b) conventional organometallic syntheses using organo-lithium or -magnesium reagents and [π-Cp₂Ti^IIICl]₂. The preferred route is via an organolithium reagent, since chemical reduction gives a mixture of products. Green, monomeric complexes (R = CH₂Si(CH₃)₃, C₆F₅) were isolated and characterised. From the reaction of π-Cp₂Ti^IVCl₂ and trimethylsilylmethyllithium in a 1/1 ratio, π-CpTi^IV [CH₂Si(CH₃)₃]₃ was obtained. Unlike π-Cp₂Ti^IIIC₆F₅, π-Cp₂Ti^IIICH₂Si(CH₃)₃ does not form a blue complex with molecular nitrogen.     

Zero-Field Splittings and Redox Potentials in an Isostructural Series of Dinuclear FeIITiIV,FeIIITiIV, and MnIITiIV Complexes with a Face-Sharing Bridging Motive

The ligand H₆ioan has been used to synthesize the three dinuclear complexes [(ioan)Mn^IITi^IV], [(ioan)Fe^IITi^IV], and [(ioan)Fe^IIITi^IV]⁺. The face-sharing bridging mode of the three phenolates provides short M-Ti^IV distances of ≈3.0 Å. Mössbauer spectra of [(ioan)Fe^IIITi^IV]⁺ show a magnetically split six-line spectrum at 3 K in zero magnetic field demonstrating a slow magnetic relaxation. Magnetic measurements provide a zero-field splitting of |D|=5 cm⁻¹ in [(ioan)Fe^IITi^IV]. EPR spectroscopy demonstrates sizable zero-field splittings of the S=5/2 spin systems of [(ioan)Mn^IITi^IV] (D=0.246 cm⁻¹) and [(ioan)Fe^IIITi^IV]⁺ (D<−1 cm⁻¹) that can be related to enforced covalency of the M-O^ph bonds. [(ioan)Fe^IIITi^IV]⁺ exhibits a reversible reduction at −0.26 V vs. Fc⁺/Fc demonstrating the facile accessibility of Fe^III and Fe^II. In contrast to an irreversible oxidation in [(ioan)Ni^IITi^IV] at 0.78 V vs. Fc⁺/Fc, the reversible oxidation at 0.25 V vs. Fc⁺/Fc in [(ioan)Mn^IITi^IV] indicates even the access of Mn^III. These results indicate that pentanuclear complexes [(ioan)FeM¹M²M¹Fe(ioan)]ⁿ⁺ are meaningful targets to access electron delocalization in mixed-valence systems over five ions due to the facile accessibility of both Fe^II and Fe^III in the terminal positions. This study provides important local spin-Hamiltonian and Mössbauer parameters that will be essential for the understanding of the potentially complicated electronic structure in the anticipated pentanuclear complexes.     

A comparative DFT study on the mechanism of olefin epoxidation catalyzed by substituted binuclear peroxotungstates ([SeO4WO(O2)2MO(O2)2]n− (M = TiIV,VV, TaV,MoVI, WVI,TcVII, and ReVII))

The selective epoxidation of olefins catalyzed by substituted binuclear peroxotungstates ([SeO₄WO(O₂)₂MO(O₂)₂]^n? (M = Ti^IV, V^V, Ta^V, Mo^VI, W^VI, Tc^VII, and Re^VII)) are investigated at the density functional theory level. The computational results reveal that the activation barrier corresponding to the oxygen transfer to the ethylene step decreases with M = V > Ti > Ta > Mo > W > Tc > Re. The Re and Tc substituted species can effectively improve the catalytic activity with lower Gibbs free energy barriers of 22.53 and 25.82 kcal/mol relative to the others under normal conditions. This suggests that Re and Tc center peroxo complexes would improve the catalytic performance. The higher activity of the substituted species is directly attributed to the lower energy of the σ*(O? O) orbital. The reaction barriers in epoxidation process are rationalized by analyzing the atomic charge, the O? O bond length, and the interaction between the substituted metal and the peroxo group of the precursor complexes. © 2013 Wiley Periodicals, Inc.     

Synthesis and spectral properties of titanium(iv) polynuclear hydroxo complexes stabilized in solution by the [PW11O39]7− heteropolyanion

Unsaturated heteropolyanions (HPA) [PW₁₁O₃₉]⁷⁻ stabilize Ti^IV hydroxo complexes in aqueous solutions (Ti: PW₁₁ [PW₁₁O₃₉]⁷⁻⪯12, pH 1–3). Spectral studies (optical,¹⁷O and³¹P NMR, and IR spectra) and studies by the differential dissolution method demonstrated that Ti^IV hydroxo complexes are stabilized through interactions of polynuclear Ti^IV hydroxo cations with heteropolyanions [PW₁₁TiO₄₀ ⁵⁻ formed. Depending on the reaction conditions, hydroxo cations Ti _n−1O _x H _y ^m+ either add to oxygen atoms of the W−O−Ti bridges of the heteropolyanions to form the complex [PW₁₁TiO₄₀·Ti _n−1O _x H _y ] ^k− (at [HPA]=0.01 mol L⁻¹) or interact with Ti^IV of the heteropolyanions through the terminal o atom to give the polynuclear complexes [PW₁₁O₃₉Ti−O−Ti _n−1O _x H _y ]^q− (at [HPA]=0.2 mol L⁻¹). When the complexes of the first type were treated with H₂O₂, Ti^IV ions added peroxo groups. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 914–920, May, 1997.     

A computational study and fragment analysis of the back-bonding in Titanocenyl Complexes containing a five-member L,L′-cyclic ligand, L,L′ = O,O′; S,S′ or Se,Se′

A DFT computational study is performed on different Cp₂Ti^IV(L,L′-BID) complexes with L,L′-BID = dioxolene, dithiolene or diselenolene. A fragment analysis of the titanocene-ligand bonding in the DFT optimized geometries showed that out of plane folding for maximum Ti ← L π donation increases Cp₂Ti^IV(O,O′-BID) (35°) < Cp₂Ti^IV(S,S′-BID) (43–49°) < Cp₂Ti^IV(Se,Se′-BID) (48–53°).     

Synthesis,Structures, and Properties of Crystalline Salts with Radical Anions of Metal‐Containing and Metal‐Free Phthalocyanines

Radical anion salts of metal‐containing and metal‐free phthalocyanines [MPc(3?)]^.?, where M=Cu^II, Ni^II, H₂, Sn^II, Pb^II, Ti^IVO, and V^IVO ( 1 – 10 ) with tetraalkylammonium cations have been obtained as single crystals by phthalocyanine reduction with sodium fluorenone ketyl. Their formation is accompanied by the Pc ligand reduction and affects the molecular structure of metal phthalocyanine radical anions as well as their optical and magnetic properties. Radical anions are characterized by the alternation of short and long C?N_imine bonds in the Pc ligand owing to the disruption of its aromaticity. Salts 1 – 10 show new bands at 833–1041 nm in the NIR range, whereas the Q‐ and Soret bands are blue‐shifted by 0.13–0.25 eV (38‐92 nm) and 0.04–0.07 eV (4–13 nm), respectively. Radical anions with Ni^II, Sn^II, Pb^II, and Ti^IVO have S=1/2 spin state, whereas [Cu^IIPc(3?)]^.? and [V^IVOPc(3?)]^.? containing paramagnetic Cu^II and V^IVO have two S=1/2 spins per radical anion. Central metal atoms strongly affect EPR spectra of phthalocyanine radical anions. Instead of narrow EPR signals characteristic of metal‐free phthalocyanine radical anions [H₂Pc(3?)]^.? (linewidth of 0.08–0.24 mT), broad EPR signals are manifested (linewidth of 2–70 mT) with g‐factors and linewidths that are strongly temperature‐dependent. Salt 11 containing the [Na^IPc(2?)]^? anions as well as previously studied [Fe^IPc(2?)]^? and [Co^IPc(2?)]^? anions that are formed without reduction of the Pc ligand do not show changes in molecular structure or optical and magnetic properties characteristic of [MPc(3?)]^.? in 1 – 10 .     

Darstellung und Kristallstruktur von TICu[CuO2]

Investigations on Electronically Conducting Oxide Systems. XVI. Solid Solutions and Conductivity in the System MgTi₂O₅? Ti₃O₅ Solid solution formation is reported for the system Mg_1–xTi_2–x^IVTi_2x^IIIO₅. With increasing x there is at room temperature a transition from the orthorhombic pseudobrookite structure to the monoclinic low-temperature modification of Ti₃O₅. The X-ray diffraction pattern results are supported by DSC measurements, electrical and magnetic investigations. The tendency of Ti? Ti pair formation in the low-temperature Ti₃O₅ structure is accompanied by a drop of the activation energy for electrical conductivity and a decreasing susceptibility at high Ti^III concentrations.     

Magnetische Ordnungsphänomene in den Clusterverbindungen Ti7Cl16 und Ti7Br16

Magnetic Ordering Phenomena in the Cluster Compounds Ti₇Cl₁₆ and Ti₇Br₁₆ The magnetic susceptibilities of Ti₇Cl₁₆ and Ti₇Br₁₆ have been measured between 3.8 and 295 K by the Faraday method. The compounds show magnetic ordering points at 15.9 and 13.5 K, respectively. The determination of the oxidation states of the titanium ions and the exchange interactions between them is complicated by the fact that at room temperature competing antiferro-magnetic intra- and intercluster exchange interactions are already present. Calculations with simple models agree with the assumption that the compounds consist of Ti₃ clusters with Ti^II and isolated Ti^IV ions.