Titanium Oxo Research Articles

Synthesis and reactivity of hydrazido(2-) and imido derivatives of titanium(IV) tetratolylporphyrin.

Titanium porphyrin hydrazido complexes (TTP)Ti = NNR2 (TTP = meso-tetra-p-tolylporphyrinato dianion; R = Me (1), Ph (2)) were synthesized by treatment of (TTP)TiCl2 with 1,1-disubstituted hydrazines H2NNR2 (R = Me, Ph) in the presence of piperdine. The nucleophilic character of the hydrazido moiety was demonstrated in the reactions of complexes 1 and 2 with p-chlorobenzaldehyde, which yielded the titanium oxo complex (TTP)-Ti = O and the respective hydrazones. Protonation of complexes 1 and 2 with phenol or water produced the 1,1-disubstituted hydrazine along with (TTP)Ti(OPh)2 or (TTP)Ti = O, respectively. Similar reactivity of p-chlorobenzaldehyde and phenol with (TTP)Ti = NiPr, 3, was observed. The reaction of complex 3 with nitrosobenzene cleanly formed the azo compound iPrN = NPh and the terminal oxo product (TTP)Ti = O.

Preparation of a mesoporous high surface area titanium oxo phosphate via a non-ionic surfactant route

Abstract Since the development of the first mesoporous silica materials by scientists of Mobil Oil [J.S. Beck, US Patent (Mobil Oil Corporation) 5, 057 (1991) 296], the synthesis principle has been applied to other metal oxides. Here, we report a new mesoporous titanium oxo phosphate, which is synthesized by a non-ionic template route (N 0 I 0 ). The formation of the mesoporous structure is dominated by hydrogen bonding between self-assembled surfactant micelles and inorganic precursors. A low-cost industrial polyethylenoxide named Dodecanol +5 EO (BASF) was used as a non-ionic surfactant. The N 2 -adsorption isotherm reveals the existence of mesoporosity in these titanium oxo phosphates with a type IV isotherm and a BET-surface area of 350 m 2 g −1 , with pore sizes calculated to be approximately 4.5 nm. The materials are thermally stable up to 550°C, among the highest temperatures reported for very high surface area mesoporous oxides so far.

Surface and bulk characterisation of titanium–oxo clusters and nanosized titania particles through 17O solid state NMR

For the first time, titanium–oxo based nano-objects have been probed using 17 O MAS and 3Q-MAS NMR. Three titanium oxo–organo clusters {[Ti 12 O 16 (OPr i ) 16 ], [Ti 16 O 16 (OEt) 32 ] and [Ti 18 O 22 (OBu n ) 26 (acac) 2 ]}, and monodisperse nanoparticles of titania anatase having 20 and 30 A oxide core diameters, have been characterised by 17 O NMR. This study shows that in titanium oxo-based compounds, the µ 2 -O sites are dominated by a significant chemical shift anisotropy, an interaction that is much weaker for the other µ n -O sites (n = 3, 4, 5). For all µ n -O sites (n = 2, 3, 4 or 5), the 17 O NMR linewidths are dominated by chemical shift distribution with a minor contribution from second order quadrupolar broadening. However, depending on the degree of distortion from tetrahedral geometry, the µ 3 -O sites can also be sensitive to second order quadrupolar effects. Bulk µ 3 -O and surface oxo species (µ 3 -O, µ 2 -O and acac–Ti) present in titania anatase nanoparticles are identified and clearly assigned. The ratio between bulk and surface species decreases as the particle size is increased. The surface reconstruction of the nanoparticles in the presence of 17 OH 2 enriched moist air, at room temperature, is demonstrated by 17 O MAS NMR experiments. From these experiments the µ 3 -O, µ 2 -O, Ti–OH, acac–Ti and H 2 O → Ti surface species were identified.

Syntheses and single-crystal structures of novel soluble phosphonato- and phosphinato-bridged titanium oxo alkoxides

The reactions of PhP(O)(OH)2 or Ph2P(O)OH with Ti(OPri)4 in DMSO give the soluble tetranuclear complexes [Ti4(µ3-O)(OPri)5(µ-OPri)3(PhPO3)3]·DMSO 1 or [Ti(µ3-O)(OPri)(Ph2PO2)]4·0.5DMSO 2, the first examples of phosphonato- and phosphinato-bridged titanium oxo alkoxides, which have been characterised by single-crystal X-ray diffraction.

Cycloaddition reactions of titanium and zirconium imido, oxo and hydrazido complexes supported by tetraaza macrocyclic ligands ‡

The tetraaza macrocycle-supported titanium and zirconium imido complexes [Ti(NR)(Mentaa)] [R = But, Ph, Tol or 4-C6H4NO2; n = 4 or 8 where H2Mentaa = tetra- or octa-methyldibenzotetraaza[14]annulene, respectively] and [Zr(NC6H3Pri2-2,6)(py)(Me4taa)] react with isocyanates or carbon dioxide to form cycloaddition products generally of the type [M{N(R)C(O)E}(Mentaa)] (M = Ti or Zr, R = aryl or tert-butyl, E = O, NBut or N–aryl). The complex [Zr{N(C6H3Pri2-2,6)C(O)N(But)}(Me4taa)] is also formed by reaction of the bis(arylimide) [Zr(NHC6H3Pri-2,6)2(Me4taa)] with ButNCO. The crystal structures of [Ti{N(Tol)C(O)O}(Me4taa)] (Tol = p-tolyl) and [Zr{N(C6H3Pri2-2,6)C(O)N(But)}(Me4taa)] are described. The tert-butyl imido complexes [Ti(NBut)(Mentaa)] (n = 4 or 8) react with Ph2NNH2 to give the corresponding terminal N,N-diphenylhydrazido derivatives [Ti(NNPh2)(Mentaa)] and these yield the cycloaddition products [Ti{N(NPh2)C(O)O}(Mentaa)] or [Ti{N(NPh2)C(O)N(Tol)}(Me4taa)] with CO2 or TolNCO, respectively. The related titanium oxo complexes [Ti(O)(Mentaa)] (n = 4 or 8) react with p-tolyl isocyanate to form the N,O-carbamate products [Ti{N(Tol)C(O)O}(Mentaa)], and with ditolylcarbodiimide to form the N,N-ureate derivative [Ti{N(Ph)C(O)N(Ph)}(Mentaa)] in which complete rupture of the TiO linkage has occurred. Reaction of the N-phenyl-N-tolyl (asymmetric) ureate [Ti{N(Ph)C(O)N(Tol)}(Me4taa)] with an excess of PhNCO gave quantitative conversion to the N,N-symmetric product [Ti{N(Ph)C(O)N(Ph)}(Me4taa)] and TolNCO. Crossover NMR tube experiments suggest that this reaction occurs via an associative mechanism.

Synthesis through an in situ esterification process and characterization of oxo isopropoxo titanium clusters

Three titanium oxo-isopropoxo clusters Ti 6O 4(OOCCH 3) 4(OPr 1) 12 ( 1), Ti 12O 16(OPr 1) 16 ( 2) and Ti 12O 16(OPr 1) 16·1.4CH 2Cl 2 ( 3) are obtained by refluxing Ti(OPr 1) 4 with 1.2 equivalents of carboxylic acids over two days. The molecular structures of Ti 6O 4(OOCCH 3) 4(OPr 1) 12 ( 1) and Ti 12O 16(OPr 1) 16· 1.4CH 2Cl 2 ( 3) have been resolved by single crystal X-ray diffraction. The titanium oxo organo cores of these clusters are also characterized in solution by 17O NMR spectroscopy and in solid-state by 13C CP MAS NMR spectroscopy.

Characterisation of sol–gel derived titanium oxopolymers: first evidence of Ti–OH groups through1H–17O CP NMR experiments

Titanium oxo based xerogels obtained through hydrolysis of titanium tetrabutoxide in acidic conditions have been characterised through FTIR,17O MAS and 1H–17O static CP NMR experiments. This latter technique allows the separation of the 17O NMR resonances corresponding to the protonated titanium oxo sites from those of the titanium oxo unprotonated sites, by varying the 1Hto 17O contact time in a cross-polarisation sequence. These experiments clearly evidence the presence of Ti–OH groups. Their characteristic 17O NMR resonance, in titanium based xerogels, is located at about 200 ppm.

Preparation, solution behaviour and electrical properties of octasubstituted phthalocyaninato and 2,3-naphthalocyaninato oxotitanium(IV) complexes

The octasubstituted oxo(phthalocyaninato)titanium(iv) complexes TiO[Pc′(CH2OC5H11)8 ] (Pc′=2,3,9,10,16,17,23,24-octasubstituted phthalocyaninate) and TiO[Pc″(OC4H9)8 ] (Pc″=1,4,8,11,15,18,22,25-octasubstituted phthalocyaninate) and the first 2,3,-naphthalocyaninato titanium complex TiO[Nc′(C6H13)8 ] (Nc′=2,5,11,14,20,23,29,32-octasubstituted naphthalocyaninate) have been prepared by treating the corresponding dicyano-benzenes or -naphthalene with titanium(iv) ethoxide and urea in n-pentanol. These compounds and their analogues TiO[Pc′(R)8 ] (R=C7H15 , OC5H11) tend to form molecular aggregates in solutions and the effects of solvent and concentration on their aggregation behaviour were investigated by UV–VIS and 1H NMR spectroscopy. The electrochemistry and electrical properties of these compounds were also studied.

Binding of a meso-Octaethyl Tris(pyrrole)−Mono(pyridine) Ligand to Titanium(III) and Titanium(IV): A Monomeric Titanium(IV) Oxo Bis(pyridine)−Bis(pyrrole) Complex Derived from the C−O Bond Cleavage of Carbon Monoxide

The reaction of a TiMe species with carbon monoxide occurred with the complete cleavage of the CO bond and formation of the TiO unit, while the [MeC] fragment homologated a pyrrole to a 4-methylpyridine ring within the meso-octaethyl tris(pyrrole)−mono(pyridine) macrocycle.

Titania–Silica Mixed Oxides: V. Effect of Sol-Gel and Drying Conditions on Surface Properties

Mesoporous titania–silica aerogels have been prepared by an alkoxide–sol-gel process with ensuing supercritical drying which involved either semicontinuous extraction using supercritical CO2or transferring the solution–sol-gel liquid directly into the supercritical state. Surface properties of these materials were compared to those of conventionally dried titania–silica xerogel. The influence of several important preparation parameters (hydrolysis route, Ti-content, and drying method) on surface properties of the gels were investigated by temperature-programmed reaction and desorption (TPRD) of isopropanol and X-ray photoelectron spectroscopy (XPS). The information gained by these surface-sensitive methods was interpreted in the light of previous bulk structural investigations, i.e., X-ray diffraction, FTIR, FTRaman, and UV–vis spectroscopy. Up to 723 K, three TPRD peaks were identified and assigned to the different surface species in titania–silica mixed oxides found in previous structural investigations: inactive silica domains, titania domains, and highly dispersed Ti in silica (Si–O–Ti linkages). The Ti-containing surface species catalyzed dehydration of isopropanol to propene at different temperatures. Depending on the dispersion and nature of titanium oxo species on the surface of the titania–silica sol-gel mixed oxides (Si–O–Ti heteroconnectivity), significant differences in the reaction-desorption profiles were observed. Prehydrolysis of the silicon alkoxide had no influence on the relative abundance of Si–O–Ti connectivity inferred from FTIR. However, XPS and TPRD revealed that the Ti-concentration on the surface increased when prehydrolysis had been applied. An increase in the bulk titania content of the mixed oxides resulted in a concomitant rise in both the surface Ti/Si ratio and the relative contribution of Si–O–Ti linkages. All titania–silica gels showed enrichment of the surface with silica. This behavior strongly depended on the drying procedure applied. Low-temperature supercritical drying and evaporative drying yielded higher titania surface concentration (lower Si enrichment) compared to high-temperature supercritical drying.

Utilization of a Cobalt Carbonyl Cluster Carboxylic Acid in the Isolation of Novel Titanium(IV) Oxo Alkoxy Carboxylates

The reaction of (CO)9Co3(μ3-CCOOH) with Ti(OR)4 results in the formation of Ti(IV) oxo alkoxy carboxylates exhibiting new structural forms: R = Et, Ti6(μ3-O)4(μ-OEt)4(OEt)8{μ-(CO)9Co3(μ3-CCO2)}4 (1); R = Pri, Ti4(μ3-O)4(OPri)4{μ-(CO)9Co3(μ3-CCO2)}4 (3); R = Ph, Ti4(μ3-O)4(OPh)4{μ-(CO)9Co3(μ3-CCO2)}4 (5); reaction with Ti(OPri)2(1,2-O2C6H4) yields Ti6(μ3-O)2(μ-O)2(μ-OPri)2(OPri)2(O2C6H4)4{μ-(CO)9Co3(μ3-CCO2)}4 (4). Observed stoichiometries and structures reflect the effects of a metal cluster relative to organic substituents.

Room temperature perovskite production from bimetallic alkoxides by ketone assisted oxo supplementation (KAOS)

Barium titanate has been prepared at room temperature from a well-characterized crystalline barium titanium oxo alkoxide by reaction with acetone. An aldol condensation apparently supplies oxygen to condensing oxo alkoxide clusters. Transmission electron microscopy confirms that the crystallites so formed are dense and perfect with an average size of approximately 85 Å. Characterization of reactants and products provides a tentative understanding of structural evolution and the intermediates of the transformation. Crystalline SrTiO3 and BaZrO3 were also formed at room temperature by this same method.

An octameric titanium oxo metallacycle with host–guest interactions

Treatment of TiCl4 with carboxylic acids RCO2H (R = C6F5, CH2C6F5, CH2OC6F5) yields a series of titanium oxo compounds; the X-ray molecular structure of [TiO(O2CC6F5)2] reveals an octameric unit and a unique 16-membered Ti8O8 ring, with two toluene molecules encapsulated above and below the ring in the molecular cavity.

Rheological study of titanium oxide-based gels

Dynamic rheological measurements have been performed on two different titanium oxo polymers based gels. These titanium oxide based gels were obtained from hydrolysis of the same molecular precursor titanium butoxide (Ti(OBu n) 4) using inorganic acids or complexing ligands such as acetylacetone as chemical additives. Dynamic rheological measurements are very sensitive and revealed differences between the sol-gel behavior of these two gels which are reflective of the difference in the synthetic conditions. The acid catalyzed gel is a highly chemically cross-linked polymeric system. The gel obtained in presence of complexing ligands is a weakly cross-linked particulate gel which rheological moduli are close to those of a liquid far after the gel point.

Reactions of titanium tetrachloride with carboxylic acids. Crystal and molecular structure of the dinuclear titanium oxo compound [{TiCl2(O2CBut)(ButCO2H)}2O

Reaction of TiCl4(1 mol) with 2,2-dimethylpropanoic acid (2.5 mol) at room temperature yields the dinuclear oxo-bridged species [{TiCl2(O2CBut)(ButCO2H)}2O]1 which has been fully characterised by an X-ray crystal structure analysis. The two metal atoms are bridged by the oxo and two carboxylate groups, which with a co-ordinated acid molecule and two chlorine atoms on each titanium gives a slightly distorted octahedral environment around each metal centre. At 40 °C compound 1 decomposes to the trinuclear species [Ti3Cl3(O2CBut)5O2], and at higher temperatures (100–120 °C) to another dinuclear oxo derivative [{TiCl(O2CBut)2}2O] which can also be obtained from the action of 2,2-dimethylpropanoic anhydride on TiCl4 in refluxing toluene. Acetic acid produces a similar, but less soluble, species to 1. Aromatic acids react differently; para-substituted aryl acids generally yield trinuclear compounds [Ti3Cl3(O2CC6H4X-p)5O2](X = Cl or Br) although the p-But acid forms [{TiCl(O2CC6H4But-p)2}2O]. In contrast the ortho-and meta-substituted acids react to give either [Ti3Cl4(O2CR)4O2](R = C6H4Cl-o or -m) or [Ti4Cl5(O2CR)7O2](R = C6H4Me-o) derivatives.

Synthesis of new titanium–oxo cluster compounds: X-ray structure of the tetranuclear oxide [Ti4Cl6(µ2-O2CPh)6(µ3-O)2

Titanium–oxo cluster compounds can be obtained in high yields by the action of carboxylic acids on titanium tetrachloride; X-ray structure analysis of the benzoate derivative [Ti4Cl6(µ2-O2CPH)6(µ3-O)2] reveals the presence of a previously unknown Ti4O2 core structure.

Acyl CO bond cleavage in Cp *2TiCOR compounds: formation of benzene derivatives by Cp *-ring expansion involving incorporation of the acyl carbon atom (Cp * = η 5-C 5Me 5)

Reaction of Cp * 2TiR (R = CH 3, neo-C 5H 11) with CO gives labile acyl compounds Cp * 2TiCOR. The latter react with (CpMo(CO) 3) 2 to yield complexes Cp * 2Ti(η 2-COR)(μ-OC)MoCp(CO) 2, which undergo acyl CO band scission with concomitant formation of benzene derivatives at room temperature. The benzene derivatives are formed through ring expansion of the Cp * ligand by incorporation of the RC fragment of the acyl group. The acyl oxygen is incorporated into a dimeric titanium oxo complex.