Ti(AlBr4)2

Ti(AlBr₄)₂ The solid Ti(AlBr₄)₂ is prepared and its crystal structure is determined. The discussion is concerned with the change of the structure of the gaseous compound during its conversion into the solid state.     

Radical trifluoromethylation of Ti ate enolate: possible intervention of transformation of Ti(IV) to Ti(III) for radical termination

The radical trifluoromethylation of ketone Ti ate enolates gave α-CF₃ ketones in good yields. The use of excess amount of LDA and Ti(OⁱPr)₄ in the preparation of Ti ate enolates is the key to the efficient radical trifluoromethylation. Theoretical studies on the spin density of the Ti(IV) ate ketyl radical intermediate suggest the involvement of transformation from Ti(IV) ate ketyl radical intermediates to Ti(III) species in a radical termination step.     

Gas-phase interaction of thiophene with the Ti(8)C(12)(+) and Ti(8)C(12) met-car clusters

The reactivity of the Ti(8)C(12)(+) met-car cation toward thiophene was investigated using density functional theory (DFT) and mass selective ion chemistry. It is shown that the experimentally observed mass spectrum can be well described by the DFT calculations. In contrast to the weak bonding interactions seen for thiophene on a TiC(001) surface, the Ti(8)C(12)(+) met-car cation is able to interact strongly with up to four thiophene molecules with the cluster staying intact. In the most stable conformation, the thiophene molecules bond to the four low-coordinated Ti(0) sites of Ti(8)C(12)(+) via a eta(5)-C,S coordination. The stability and the activity of the Ti(8)C(12)(+) met-car is observed to increase with an increasing number of attached thiophene molecules at the Ti(0) sites, which is associated with a significant transfer of electron density from thiophene to the cluster. The additional electron density on the Ti(8)C(12)(+) cation cluster, however, is not sufficient to cleave the C-S bonds of thiophene and the dissociation reaction of thiophene is predicted to be a highly activated process. By contrast, DFT calculations for the neutral Ti(8)C(12) met-car predict that the dissociation reaction leading to adsorbed S and C(4)H(4) fragments is energetically favorable for the first thiophene molecule. The binding behavior for subsequent addition of thiophene molecules to the neutral met-car is also presented and compared to that of the cation.     

Ti(IV)-centered dynamic interconversion between Pd(II), Ti(IV)-containing ring and cage molecules

Heteronuclear, supramolecular ring and cage complexes have been constructed from a pyridyl catechol ligand, TiO(acac)2, and PdCl2(CH3CN)2. These two complexes are quantitatively interconvertible, in which Ti4+-centered coordination changes take place between a well-known Ti(catecholato)3 and a newly established TiH(catecholato)2(acetylacetonato) structures. The Ti4+-centered structural changes arise from the changes in the component fraction and basicity condition.     

Aqueous Ti(IV)-catalyzed Diels-Alder reaction

The aqueous Diels-Alder reaction of 1,3-cyclohexadiene with 1,4-benzoquinone was compared and contrasted to the same reaction catalyzed with Flextyl P, a novel Ti(IV) performance catalyst. The catalyst improved conversion by 22% versus the uncatalyzed reaction and represents a rare example of a Ti(IV) catalyzed Diels-Alder reaction in water.     

Reactivity of boranes with a titanium(IV) amine tris(phenolate) alkoxide complex; formation of a Ti(IV) tetrahydroborate complex, a Ti(III) dimer and a Ti(IV) hydroxide Lewis acid adduct

Treatment of the titanium(IV) alkoxide complex [Ti(Oi Pr)(OC6Me2H(2)CH2)3N] (2) with BH3.THF, as part of a study into the utility and reactivity of (2) in the metal mediated borane reduction of acetophenone, results in alkoxide-hydride exchange and formation of the structurally characterised titanium(iv) tetrahydroborate complex [Ti{BH4}(OC6Me2H2CH2)3N] (3). Complex (3) readily undergoes reduction to form the isolable titanium(III) species [Ti(OC6Me2H2CH2)3N]2 (4). Reaction of (2) with B(C6F5)3 results in formation of the Lewis acid adduct [Ti(OC6Me2H2CH2)3N][HO.B(C6F5)3] (5). In comparison, treatment of the less sterically encumbered alkoxide Ti(Oi Pr)4 with B(C6F5)3 results in alkoxide-aryl exchange and formation of the organometallic titanium complex [Ti(Oi Pr)3(C6F5)]2 (6). The molecular structures of 3, 4, 5 and 6 have been determined by X-ray diffraction.     

Reconsideration of serum Ti(IV) transport: albumin and transferrin trafficking of Ti(IV) and its complexes

The trafficking of titanium(IV) by human serum transferrin (HsTf) has been implicated in the physiology of this hydrolysis-prone metal. The current work broadens to include the further interactions of Ti(IV) in serum that bear on this model. Ti2HsTf (2 equiv) binds the transferrin receptor TfR1 with Kd1 = 6.3 +/- 0.4 nM and Kd2 = 410 +/- 150 nM, values that are the tightest yet measured for a metal other than iron but weaker than the corresponding ones for Fe2HsTf due to both slightly slower on rates and slightly faster off rates. Comparing the affinities of metals for HsTf with the affinities of the resulting M2HsTf species for TfR1, we speculate that the formation of an M2HsTf complex of high affinity may predict a lobe-closed conformation that leads to a favorable interaction with TfR1. Human serum albumin (HSA), an important serum competitor for metal binding, can bind up to 20 equiv of Ti(IV) supplied in several forms. With some ligands, Ti(IV) may bind to the N-terminal metal binding site of albumin, forming a ternary complex. However, the dominant type of HSA binding is via Ti(IV) in complex form, probably at surface sites. Notably, HSA greatly stabilizes the titanocene moiety of the drug candidate Cp2TiCl2 with respect to hydrolysis and precipitation. HSA binds Ti(IV) citrate supplied as a hydrolyzed or unhydrolyzed source, with 1 equiv of citrate remaining bound. Titanium(IV) monocitrate neither competes with the binding of reporter molecules known to dock at canonical drug sites I or II nor binds at the N-terminus. HsTf outcompetes HSA for soluble Ti(IV) in a direct competition, but once bound to albumin, the transfer of Ti(IV) from HSA to HsTf is quite slow. Each of these findings has implications for the metabolism of Ti(IV) in human serum.     

Platium Film Electrodes (1) Platium Film on Ti or TiO2-Covered Ti

A platium film was formed on a Ti(Pt-Ti) and on a TiO₂(Pt-TiO₂-Ti) substrate by the conventional electroplating method (ELP) and by the electroless plating technique (ELSP). The effective minimum film thickness was found to be 0.5 μm judging from the maximum electrocatalytic capablity in alkaline (1 M NaOH) water electrolysis. The film obtained from ELP is superior to that obtained from ELSP, being more tightly bound to the substrate, showing better coverage of the subsrate surface, and also being mechanically stronger. Comparisons with bright Pt and with Pt-black electrodes were made and it is concluded that the electrodes newly prepared using ELP will work as well as Pt-black electrods. The electrodes from ELSP are useful only as cathodes, and are not suitable as anodes.     

Cationic Ti(IV) and neutral Ti(III) titanocene-phosphinoaryloxide frustrated Lewis pairs: hydrogen activation and catalytic amine-borane dehydrogenation

Titanium-phosphorus frustrated Lewis pairs (FLPs) based on titanocene-phosphinoaryloxide complexes have been synthesised. The cationic titanium(IV) complex [Cp(2)TiOC(6)H(4)P((t)Bu)(2)][B(C(6)F(5))(4)] 2 reacts with hydrogen to yield the reduced titanium(III) complex [Cp(2)TiOC(6)H(4)PH((t)Bu)(2)][B(C(6)F(5))(4)] 5. The titanium(III)-phosphorus FLP [Cp(2)TiOC(6)H(4)P((t)Bu)(2)] 6 has been synthesised either by chemical reduction of [Cp(2)Ti(Cl)OC(6)H(4)P((t)Bu)(2)] 1 with [CoCp*(2)] or by reaction of [Cp(2)Ti{N(SiMe(3))(2)}] with 2-C(6)H(4)(OH){P((t)Bu)(2)}. Both 2 and 6 catalyse the dehydrogenation of Me(2)HN·BH(3).     

Ion pairing in Ti(IV) trisamidotriazacyclononane compounds

[Ti[N(Ph)SiMe2]3-tacn]X complexes (X = Cl, 1; I, 2; PF6, 3; BPh4, 4) were studied by NMR and electron absorption and emission methods, which showed that these compounds exist in bromobenzene and dichloromethane solutions as ion pairs. The significant modifications observed in the proton resonances of tacn in C6D5Br, which follow the sequence BPh(4-) > or = PF(6-) > or = I- approximately Cl-, are a qualitative indication of the strength of the interactions that depend on the anion. The reaction of 2 with LiNMe2 led to [Ti(NPh)[NPh(SiMe2)]2-tacn], 5, that forms upon attack of Me2N- at one SiMe2 group. The formation of 5 is discussed on the basis of the interactions identified in solution.     

双异丙烯基二茂金属(Sn,Ti)的合成

虽然,廿多年来各同学者对二茂铁衍生物进行了深入的研究,但却极少报道合成二茂锡衍生物,仅见1959年Wilkinson等合成双甲熬二茂锡以及Cowley等合成(Me₃SiC₅H₄)₂Sn和[(i-Pr₂N)₂PC₅H₄]₂sn,二茂钛衍生物的报道较多,但除Rausch等报道过合成低产率的乙烯基二氯二茂钛(Ⅳ)外,几乎没有报道过类似的烯烃二茂钛(Ⅳ)的合成。     

Titanium(II) and titanium(III) tetrahydroborates. Crystal structures of [Li(Et2O)2][Ti2(BH4)5(PMe2Ph)4], Ti(BH4)3(PMe2Ph)2, and Ti(BH4)3(PEt3)2

The molecular structures of the titanium(III) borohydride complexes Ti(BH4)3(PEt3)2 and Ti(BH4)3(PMe2Ph)2 have been determined. If the BH4 groups are considered to occupy one coordination site, both complexes adopt distorted trigonal bipyramidal structures with the phosphines in the axial sites; the P-Ti-P angles deviate significantly from linearity and are near 156 degrees. In both compounds, two of the three BH4 groups are bidentate and one is tridentate. The deduced structures differ from the one previously described for the PMe3 analogue Ti(BH4)3(PMe3)2, in which two of the tetrahydroborate groups were thought to be bound to the metal in an unusual "side-on" (eta(2)-B,H) fashion. Because the PMe3, PEt3, and PMe2Ph complexes have nearly identical IR spectra, they most likely have similar structures. The current evidence strongly suggests that the earlier crystal structure of Ti(BH4)3(PMe3)2 was incorrectly interpreted and that these complexes all adopt structures in which two of the BH4 groups are bidentate and one is tridentate. The synthesis of the titanium(III) complex Ti(BH4)3(PMe2Ph)2 affords small amounts of a second product: the titanium(II) complex [Li(Et2O)2][Ti2(BH4)5(PMe2Ph)4]. The [Ti2(BH4)5(PMe2Ph)4]- anion consists of two Ti(eta(2)-BH4)2(PMe2Ph)2 centers linked by a bridging eta(2),eta(2)-BH4 group that forms a Ti...(mu-B)...Ti angle of 169.9(3) degrees. Unlike the distorted trigonal bipyramidal geometries seen for the titanium(III) complexes, the metal centers in this titanium(II) species each adopt nearly ideal tbp geometries with P-Ti-P angles of 172-176 degrees. All three BH4 groups around each Ti atom are bidentate. One of the BH4 groups on each Ti center bridges between Ti and an ether-coordinated Li cation, again in an eta(2),eta(2) fashion. The relationships between the electronic structures and the molecular structures of all these titanium complexes are briefly discussed.     

Wasserstoffaufnahme und magnetisches Verhalten der intermetallischen Phasen Ti2(Ni,Co) und Ti2(Ni,Fe)

Hydrogen absorption by the intermetallic compounds Ti₂(Ni,Co) and Ti₂(Ni,Fe) with Ti₂Ni-structure (O _h ⁷ -Fd3m) is accompanied by an increase of the volume of the unit cell without any structural change, while the maximum value of absorbed hydrogen is practically independent of the alloy composition. By taking up hydrogen, the intermetallic compounds, showingPauli spin paramagnetism with complex temperature dependence, become either temperature independent paramagnetic [hydrides of Ti₂(Ni,Co)] or strongly temperature dependent paramagnetic, following a modifiedCurie-Weiss-Law [hydrides of Ti₂(Ni,Fe)], respectively.

Herrn Prof. Dr.H. Bittner zum 60. Geburtstag gewidmet.     

Synthesis and Anti-inflammatory Action of(η-C5H5)2Ti(Sal)2 and (η-C5H5)2Ti(Clo)2

Two new complexes (Cp)2Ti(Sal)2 and(Cp)2Ti(Clo)2(Cp=Cyclopentadienyl η5-C5H5), have been synthesized in anhydrous THF by the reaction of Hsal(o-hydroxybenzoic acid, salicylate acid) or Hclo[N-(m-chloro-phe-nyl) anthranili acid, acidum clofenamicum] with (Cp)2TiCl2 and characterized by means of elemental analyses, IR, 1H NMR, 13C NMR, UV and molar conductivity. In complex (Cp)2Ti(Sal)2 or (Cp)2Ti(Clo)2, the oxygen atom of the carboxyl group coordinates to Ti(IV) in a monodentate manner. The inhibitory action of the complexes on mouse ear tumefaction caused by croton oil and rat foot granulation growth caused by cotton balls is higher than that of the corresponding ligands Hsal, Hclo and [(Cp)2TiCl2], whereas their toxicity is lower than those of the free ligands.     

Tetrakis(triphenylphosphaniminato)titan, [Ti(NPPh3)4]

Tetrakis(triphenylphosphoraneiminato)titanium, [Ti(NPPh₃)₄] The title compound has been prepared by the reaction of [TiCl₂(NPPh₃)₂] with methyllithium and cyclopentadienyllithium, respectively, in hexane solution. [Ti(NPPh₃)₄] · 3 C₇H₈ crystallizes from toluene solution to form colourless, only slightly moisture sensitive crystals which were characterized by a crystal structure determination. Space group I4₁/a, Z = 8, lattice dimensions at ?80°C: a = b = 2160.7(2), c = 3334.2(3) pm, merohedral (110) twin, R = 0.077. The compound forms monomeric molecules with tetrahedrally coordinate titanium atoms and bonding parameters of TiN = 187.3 pm, PN = 155.1 pm, TiNP 150.4° in average.     

Electrochemical amination. Ti(IV)/Ti(III) mediator system in aqueous solutions of sulfuric acid

As a result of polarographic and spectrophotometric studies, and mathematical modeling, the dependence of electrochemical properties of the Ti(IV)/Ti(III) pair on the composition of the Ti(IV) complexes is established in sulfuric acid solutions. It is found that Ti(IV) in 1–17 M H₂SO₄ at the metal ion concentrations used in the process of amination of aromatic compounds can exist in the form of twelve basic complex forms, of which seven, including the binuclear and two tetranuclear ones, are observed for the first time. Ten forms are electrochemically active. An increase in the overall amount of reversibly reducing cationic mononuclear hydrosulfate complexes of Ti(IV) among these at a growing H₂SO₄ concentration results in an increase in the redox potential of the Ti(IV)/Ti(III) mediator system and therefore in an increase in the yield of the electrochemical amination products.     

Dampfdruckmessungen und Protonenresonanzuntersuchung an Hydriden der intermetallischen Phasen Ti2(Ni,Co) und Ti2(Ni,Fe)

NMR and hydrogen equilibrium pressure measurements were performed on hydrides of the intermetallic compounds Ti₂(Ni, Co) and Ti₂(Ni, Fe). The following values of enthalpy H and entropy S for the formation of the hydrides of the intermetallic phases Ti₂Co and Ti₂Ni were found: H(Ti₂CoH _y )=–47.6 kJ/mol H₂, H(Ti₂NiH _y )=–53.7 kJ/mol H₂; S(Ti₂CoH _y )=–119.8 J/(K·mol H₂), S(Ti₂NiH _y )=–127.5 J/(K·mol H₂). By substitution of Ni or Co by Fe, the values of H and S of the corresponding quaternary hydrides become less negative. An interpretation of the experimental results is tried by the model ofShaltiel and coworkers.Proton diffusion was investigated in a series of the intermetallic hydrides Ti₂(Ni, Co)H _x and Ti₂(Ni, Fe)H _x . The diffusion rate is lowered by increased Ni/Fe substitution. Substitution of Ni by Co scarcely effects the hopping process. The activation energies were found to be smaller for the Ti₂Ni-hydrides compared with the Ti₂Co-hydrides.

Herrn Prof. Dr.H. Nowotny zum 70. Geburtstag gewidmet.     

Synthesen und Strukturen der Titan(III)‐siloxane [Ti(OSiPh3)3(thf)2] und [Ti(OSiPh3)3(py)2]

Syntheses and Structures of the Titanium(III) Siloxanes [Ti(OSiPh₃)₃(thf)₂] and [Ti(OSiPh₃)₃(py)₂] The new titaniumtrioxysilanes [Ti(OSiPh₃)₃(thf)₂] ( 1 ) and [Ti(OSiPh₃)₃(py)₂] ( 2 ) have been obtained from the reaction of titaniumtrichloride with LiOSiPh₃ in the presence of the corresponding bases tetrahydrofurane (thf) and pyridine (py). From the crystal structures of both compounds it is evident that the titanium atoms are in the centres of trigonal‐bipyramidal coordination figures, with the donor atoms in axial positions. The compounds 1 and 2 have slightly different structures (mean values: 1 : Ti‐O(Si) 1.897(9), Ti‐O(C) 2.136(8) Å; 2 : Ti‐O 1.902(9), Ti‐N2.252(8) Å) and have a single absorption band in the visible region of the UV‐spectrum. The exchange of the thf‐ligands in 1 by pyridine (in high molar excess) seems to be hindered as deduced from UV‐spectroscopy.     

Atom transfer reactions of (TTP)Ti(eta 2-3-hexyne): synthesis and molecular structure of trans-(TTP)Ti[OP(Oct)3]2

Atom and group transfer reactions were found to occur between heterocumulenes and (TTP)Ti(eta 2-3-hexyne), 1 (TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion). The imido derivatives (TTP)Ti=NR (R = iPr, 2; tBu, 3) were produced upon treatment of complex 1 with iPrN=C=NiPr, iPrNCO, or tBuNCO. Reactions between complex 1 and CS2, tBuNCS, or tBuNCSe afforded the chalcogenido complexes, (TTP)Ti=Ch (Ch = Se, 4; S, 5). Treatment of complex 1 with 2 equiv of PEt3 yielded the bis(phosphine) complex, (TTP)Ti(PEt3)2, 6. Although (TTP)Ti(eta 2-3-hexyne) readily abstracts oxygen from epoxides and sulfoxides, the reaction between 1 and O=P(Oct)3 did not result in oxygen atom transfer. Instead, the paramagnetic titanium(II) derivative (TTP)Ti[O=P(Oct)3]2, 7, was formed. The molecular structure of complex 7 was determined by single-crystal X-ray diffraction: Ti-O distance 2.080(2) A and Ti-O-P angle of 138.43(10) degrees. Estimates of Ti=O, Ti=S, Ti=Se, and Ti=NR bond strengths are discussed.     

Li,Ti(III), and Ti(IV) trisamidotriazacyclononane complexes. Syntheses,reactivity, and structures

The preparations of 1,4,7-(NHPhSiMe(2))(3)-1,4,7-triazacyclononane (H(3)N(3)-tacn) and its lithium and sodium derivatives are described. The X-ray structure of the THF adduct of the lithium derivative, Li(3)N(3)-tacn(THF)(2), shows that one of the macrocycle pendant arms is bent to allow the coordination of the its lithium ion to two tacn amines. In solution, a fluxional process makes all the pending arms magnetically equivalent. The reactions of Li(3)N(3)-tacn or Na(3)N(3)-tacn with either TiCl(4) and TiCl(3)(THF)(3) led to the formation of [Ti(N(3)-tacn)], 5. The oxidation of 5 with various oxidizing reagents gave cationic complexes [Ti(N(3)-tacn)]X, 6 (X = I, Cl, SCN, PF(6), BPh(4)), that exist as a pair of enantiomers, lambda(lambdalambdalambda)/delta(deltadeltadelta), which interconvert in solution. The molecular structures of 5 and 6 (X = I, BPh(4)) show the coordination of the six nitrogen donor set to the titanium. Due to the short length of the tacn pendant arms, the hexadentate bonding mode of the ligand is mainly achieved through the sharpening of the N-Si-N angles. The reaction of [Ti(N(3)-tacn)]I, 6a, with W(CO)(6) led to the synthesis of [Ti(N(3)-tacn)][W(CO)(5)I], 7.