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PubMed1997

Aneurysm clips made of titanium: magnetic characteristics and artifacts in MR.

PURPOSE: To evaluate the magnetic characteristics, artifact formation, and implant safety of titanium aneurysm clips for use in MR imaging. METHODS: Aneurysm clips made of titanium alloy TiAl6V4 were tested in a magnetometer to determine their magnetic susceptibility and in a 1.5-T MR imager using both a geometric phantom and an animal model. A commercially available alpha-Phynox clip served as the reference standard. RESULTS: We found minimal magnetization and a significant reduction in image artifacts with the titanium clip as compared with the Phynox clip. CONCLUSION: The titanium clips improve image quality, biocompatibility, and patient safety in medical MR applications.

Aneurysm↗
PubMedDate not supplied

Passive film growth on titanium alloys: physicochemical and biologic considerations.

The role of reactive oxygen derivatives (hydroxy peroxide, hydroxyl radical, and singlet oxygen) on the precipitation of inorganic and organic complexes onto the surface of titanium implant alloys is discussed in this review. In addition, the effect of possible implication of several biologic entities surrounding the implant on the implant-tissue interface constituents is described. Evidence from relevant studies suggests that local microenvironmental byproducts and factors associated with the inflammatory response resulting from the implant-induced tissue insult may enhance the expressivity of the inherent, clinically important property of titanium to form oxides. Growth of titanium oxide may be explained through several processes derived from biologic, thermodynamic, and electrochemical approaches. The models proposed to interpret this phenomenon are often contradictory, demonstrating inward or outward from the bulk material passive film growth, with increasing or self-limiting levels of oxide formation as a function of time. However, in vivo observations are consistent with aging-induced thickening of the complexes precipitated on the implant material surface. This review attempts to clarify several critical issues pertaining to passive film formation and kinetics on titanium-alloy surfaces.

Alloys↗
PubMed1997

[The three-dimensional titanium miniplate rigid fixation in the treatment of fracture of maxilla].

The three-dimensional (3-D) Titanium miniplate system is one of the newest internal rigid fixation for the maxillo-mandibular surgery in recent years. The geometry of the plate assures a good stability in the three-dimensions of the fracture sits. Thirty patients suffering from maxillo-mandibular fractures had been operated on using the 3-D Titanium miniplates since 1991. The group of the patient included 16 cases of mandibular fractures, 8 cases of maxillary fractures and 6 cases of maxillo-mandibular fracture. All of the patient had very good result without any complication. The follow-up was 6 months to 3 years. The 3-D Titanium miniplate as an ideal easy to use, good resistance against torque forces and, compact forms of the miniplate were the some of the advantages. Clinical examples had been provided to illustrate the actual usage of the 3-D miniplate in the field of the surgical treatment for the maxillo-mandibular fracture. It is the author's opinion that the internal rigid fixation by 3-D Titanium miniplates is a promising method of treating fractures of the maxilla and is to be better tolerated by the patients and surgeons.

Adolescent↗
PubMed2001

Syntheses, structure, and reactivity of chiral titanium compounds: procatalysts for olefin polymerization.

Titanium complexes with chelating alkoxo ligands have been synthesised with the aim to investigate titanium active centres in catalytic ethylene polymerisation. The titanium complexes cis-[TiCl2(eta2-maltolato)2] (1, 89%), and cis-[TiCl2(eta2-guaiacolato)2] (2, 80%) were prepared by direct reaction of TiCl4 with maltol and guaiacol in toluene. The addition of maltol to [Ti(OiPr)4] in THF results in the formation of species [Ti(OiPr)2(maltolato)2] (3, 82%). The titanium compound cis-[Ti(OEt)2(eta2-maltolato)2] (4, 74%) was obtained by the transesterification reaction of species 3 with CH3CO2Et. When compound 4 is dissolved in THF a dinuclear species [Ti2(mu-OEt)2(OEt)4-(eta2-maltolato)2] (5, 45%) is formed. Reaction of [Ti(OiPr)4] with crude guaiacol in THF yields a solid, which after recrystallisation from acetonitrile gives [Ti4(mu-O)4(eta2-guaiacolato)] x 4CH3CN (6, 55%). In contrast, reaction of TiCl4 with crude guaiacol in tetrahydrofuran affords [Ti2(mu-O)Cl2(eta2-guaiacolato)4] (7, 82%). Crystallographic and electrochemical analyses of these complexes demonstrate that maltolato and guaiacolato ligands can be used as a valuable alternative for the cyclopentadienyl ring. These complexes have been shown to be active catalysts upon combination with the appropriate activator.

Journal Article↗
PubMed2001

One-step synthesis of a highly active, mesoporous, titanium-containing silica by using bifunctional templating.

A highly active, three-dimensional, mesoporous titanosilica, TiTUD-1, with comparable properties to Ti-grafted mesoporous silica MCM-41, has been prepared in a one-step synthesis. A non-surfactant chemical, triethanolamine, was used as a template molecule. Triethanolamine easily forms complexes with titanium alkoxides, yielding titanatrane complexes, which together with free triethanolamine form meso-sized aggregates that template mesopores upon increasing the temperature of the synthesis mixture. Triethanolamine served as both mesopore template and ligand for the titanium complexes, which represent the majority of the catalytic-site precursors. The formation of the silica network and the titanium insertion were followed by a combination of diffuse reflectance UV/ Vis/NIR and FTIR spectroscopy. A titanium-rich phase was obtained on the mesopore surfaces during calcination, allowing for easy accessibility of the reactants to the catalytic sites. TiTUD-1 is about six times more active than framework-substituted Ti-MCM-41 and has similar activity to Ti-grafted MCM-41.

Journal Article↗
PubMed1997

Surface and Structural Properties of Novel Titanium Phosphates

Two novel fibrous framework titanium phosphates having a similar formula, Ti2O(PO4)2·H2O, and a layered titanium phosphate, Ti2O3(H2PO4)2·2H2O, were synthesized and their properties were characterized with physicochemical methods, such as elemental analysis, thermogravimetry, nitrogen adsorption, X-ray diffraction, and 31P solid-state NMR. Nitrogen adsorption isotherms were measured on synthesized titanium phosphates in order to characterize their surface and structural properties. The specific surface area and total pore volume of the titanium phosphates studied were determined. The low-pressure nitrogen adsorption isotherms were used to evaluate surface heterogeneity of the synthesized materials by employing an advanced numerical procedure based on the regularization method.

Journal Article↗
PubMed1997

Cationic Surfactant Adsolubilization of 2-Naphthol and Naphthalene with Titanium Dioxide Having Dodecyl Chain

Adsolubilization of 2-naphthol and naphthalene by cationic surfactant-adsorbed layers formed on titanium dioxides with or without a dodecyl chain was investigated. The cationic surfactants used were dodecyltrimethylammonium bromide and 1,2-bis(dodecyldimethylammonio) ethane dibromide (2RenQ). It was found that the adsolubilized amounts of 2-naphthol and naphthalene increase and reach a maximum and then decrease for both surfactants and titanium dioxides with or without the dodecyl chain, where in the absence of surfactants the incorporated amount of naphthalene on the titanium dioxide with the dodecyl chain is markedly large. The adsolubilized amounts of 2-naphthol and naphthalene were enhanced with the titanium dioxide with the dodecyl chain by adsorption of surfactants, in particular 2RenQ. The admicellar partitioning coefficients also showed that naphthalene is adsolubilized preferentially rather than 2-naphthol and the surface treatment with the dodecyl chain enhances the adsolubilization for two adsolubilizates. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed2001

Rheological Behavior of Titanium Dioxide Suspensions.

The rheological properties of titanium dioxide dispersed in water are measured over a wide range of powder concentrations, temperatures, and pH values. The value of intrinsic viscosity of titanium dioxide measured with an Ubbelohde capillary viscometer is 3.55, which is useful for determining the shape and aggregation property of the particles. The yield stress and steady shear viscosity of titanium dioxide with broad and narrow particle size distributions were measured over a wide range of solid volume fractions on a Brabender rheometer. It is observed that the rheological properties of the suspensions are quite different due to the difference in particle size distributions. Quemada, Casson, and Zhou's models were used to fit the experimental data and useful parameters were obtained. Calculated data are also in good agreement with the experimental data. As expected, the shear viscosity and yield stress decrease with increasing temperature. But when the temperature is around 50 degrees C, yield stress increases with increasing temperature while shear viscosity exhibits a complex behavior. The phenomena are very interesting and special. The Peclet number was used to analyze the shear thickening behavior. Models were also used to describe the shear viscosity under different temperatures and the master plots of the reduced variables eta/eta(infinity) vs t(c)gamma; at different temperatures are superimposed, which means the agreement is fair and the models are suitable to describe the rheological properties of titanium dioxide suspensions. pH effects were investigated on a Rheometrics RFS-II rheometer and it was found that pH can change the surface charge of the particles, which also affects the rheological behavior. The pH at which maximum shear viscosity and yield stress occur is in concordance with the isoelectric point. Copyright 2001 Academic Press.

Journal Article↗
PubMed1995

The effect of electrical perturbation on osseointegration of titanium dental implants: a preliminary study.

PURPOSE: Successful osseointegration of titanium dental implants is decreased in areas of poor bone volume and density. Low amperage direct current (LADC) has been shown to perturb bone cells, which in turn promotes bone growth. The purpose of this experiment was to evaluate the effect of LADC on the osseointegration of endosseous titanium dental implants. MATERIALS AND METHODS: Two implant sites were prepared in the body of the mandible of five rabbits by an extraoral approach. An LADC-stimulated 3.75 x 7 mm-titanium implant was placed in one site and an identical control implant was inserted on the contralateral side. A sterilized silicone-encased power pack producing 7.5 +/- 0.2 uA and 1.35 +/- 0.01 V was placed in a submandibular pouch. The active cathode lead was attached to the LADC implant and the anode was placed in the mandible 5 mm distal to the implant. Nonactive leads were similarly connected to the control implant. Twenty-eight days after placement, the implants were removed using a torque wrench, and the bone surrounding the implants was examined both microscopically and radiographically. RESULTS: The average force to initial rotation was 1,320 +/- 880 g/cm for the LADC-stimulated implants and 1,290 +/- 238 g/cm for the control implants. This was significantly different by t test (P = .94). Light microscopic evaluation demonstrated a mixture of compact and woven bone and fibrous tissue adjacent to both groups of implants. Histomorphometric analysis demonstrated an average percent of bone in relation to the total tissue adjacent to the control implants of 33.5 +/- 15.4 and 40.2 +/- 4.8 for the LADC-stimulated implants (not significantly different, t test, P = .39). CONCLUSION. It was concluded that LADC as used in this study does not positively affect the healing of bone. Its ability to enhance bone growth around titanium dental implants needs further investigation.

Animals↗
PubMed2005

A prospective randomized comparison of bioabsorbable and titanium anterior cruciate ligament interference screws.

PURPOSE: To compare the Phantom bioabsorbable polymer interference screw (DePuy, Warsaw, IN) with a titanium metal interference screw when used in fixation of femoral and tibial bone blocks in central third bone-patellar tendon-bone autograft anterior cruciate ligament (ACL) reconstructions. TYPE OF STUDY: Multicentered prospective randomized study. METHODS: Two surgeons performed primary ACL reconstructions at different locations. Preoperatively, the patients were randomly assigned. One group received a titanium cannulated interference screw. The second group received the cannulated poly-L-lactic bioabsorbable Phantom screw. Data included subjective evaluation of activity level and International Knee Documentation Committee scores. Objective measures were made using the KT-1000 arthrometer (MedMetric, San Diego, CA), range of motion, presence of effusions, and complications intraoperatively or postoperatively. Measurements were made at 1 year and 2 years. Radiographic evaluation was carried out at least 2 years from the initial surgical date and interpreted by 2 independent orthopaedic surgeons. RESULTS: At the 1-year follow-up (N = 97), pain was reported more during moderate activity in the Phantom screw group (6) compared with the titanium screw group (0) (P = .03). No statistical difference between range of motion (P = .45), activity level (P = .83), swelling with activity (P = .95), partial (P = .13) or full (P = .31) giving way, knee effusions (P = .33), or KT-1000 side-to-side difference (P = .53) were found. At the 2-year follow-up (N = 65), more subjects (18) in the Phantom interference screw group reported activity levels in the strenuous category compared with those in the titanium interference screws (7) group (P = .02). No differences were reported with respect to pain (P = .97), effusion (P = .17), partial (P = .28) or full (P = .27) giving way, swelling with activity (P = .21), range of motion ( P = .64), or KT-1000 side-to-side difference (P = .96). Radiographic inspection showed no change in bone plug position, osteolysis, adverse effect, or complication caused by the bioabsorbable material. Some evidence of tunnel widening was seen in both groups. CONCLUSIONS: Use of a poly-L-lactic bioabsorbable interference screw can provide clinical results equal to that of a metal interference screw for fixation of a central third bone-patellar tendon-bone graft in ACL reconstruction. LEVEL OF EVIDENCE: Level II, therapeutic.

Absorbable Implants↗
PubMedDate not supplied

Multinuclear (27Al, 29Si, 47,49Ti) solid-state NMR of titanium substituted zeolite USY.

Multinuclear solid-state NMR spectroscopy, employing 29Si MAS,27Al MAS/3Q-MAS and (47,49)Ti wide-line experiments, has been used for the structural characterization of titanium substituted ultra-stable zeolite Y (Ti-USY). 27Al MAS experiments show the presence of aluminum in four (Al(IV)), five (Al(V)), and six (Al(VI)) coordination, whereas the multiplicity within Al(IV) and Al(VI) is revealed by 27Al 3Q-MAS experiments. Two different tetrahedral and octahedral Al environments are resolved and their isotropic chemical shifts (delta(CS)) and second-order quadrupole interaction parameters (P(Q)) have been determined by a graphical analysis of the 3Q-MAS spectra. The emergence of signal with higher intensity at -101 ppm in the 29Si MAS spectrum of Ti-USY samples indicates the possible occurrence of Q4(3Si,1Ti) type silicon environments due to titanium substitution in the faujasite framework. High-field (11.74T) operation, using a probehead specially designed to handle a large sample volume, has enabled the acquisition of 47,49Ti static spectra and identification of the titanium environment in the zeolite. The chemical shielding and electric field gradient tensors for the titanium environment in the zeolite have been determined by a computer simulation of the quadrupolar broadened static 47,49Ti NMR spectra.

Journal Article↗
PubMed2004

First isolated active titanium peroxo complex: characterization and theoretical study.

The protonated titanium peroxo complex [Bu(4)N](4)[HPTi(O(2))W(11)O(39)] (1) has been first prepared via interaction of the micro-oxo dimeric heteropolytungstate [Bu(4)N](8)[(PTiW(11)O(39))(2)O] (3) with an excess of 30% aqueous H(2)O(2) in MeCN. Peroxo complex 1 has been characterized by using elemental analysis, UV-vis, IR, resonance Raman (RR), (31)P and (183)W NMR spectroscopy, cyclic voltammetry, and potentiometric titration. The electronic and vibrational spectra of 1 are very similar to those of the well-known unprotonated titanium peroxo complex [Bu(4)N](5)[PTi(O(2))W(11)O(39)] (2), while (31)P and (183)W NMR spectra differ significantly. A compilation of the physicochemical techniques supports a monomeric Keggin type structure of 1 bearing one peroxo ligand attached to Ti(IV) in a eta(2)-coordination mode. The protonation of the titanium peroxo complex results in an increase of the redox potential of the peroxo group, E(1/2) = 1.25 and 0.88 V relative to Ag/AgCl reference electrode for 1 and 2, respectively. In contrast to 2, 1 readily reacts with 2,3,6-trimethylphenol (TMP) at 40 degrees C in MeCN to give 2,2',3,3',5,5'-hexamethyl-4,4'-biphenol (BP) and 2,3,5-trimethyl-p-benzoquinone (TMBQ). The proportion between BP and TMBQ in the reaction products depends on the TMP/1 ratio. When a 2-fold excess of TMP is used, the main reaction product is BP (90%), while using a 2-fold excess of 1 leads to TMBQ (95%). On the basis of the product study, a homolytic oxidation mechanism that implicates the formation of phenoxyl radicals is suggested. The RR deuterium labeling experiments show that the activating proton is most likely localized at a Ti-O-W bridging oxygen rather than at the peroxo group. Theoretical calculations carried out at the DFT level on the protonated and unprotonated titanium peroxo derivatives also propose that the most stable complex is formed preferentially after protonation of the Ti-O-W site; however, both Ti-OH-W and TiOO-H protonated anions could coexist in solution.

Journal Article↗
PubMed2005

Preparation and crystal structures of a series of titanium(III) 9-BBN hydroborate complexes containing Ti...H agostic interactions.

9-BBN hydroborate complexes Ti{(mu-H)2BC8H14}3(THF)2 (1), Ti{(mu-H)2BC8H14}3(OEt2) (2), and [K(OEt2)4]-[Ti{(mu-H)2BC8H14}4] (4) were formed from the reaction of TiCl4 with K[H2BC8H14] in diethyl ether or THF. Ti{(mu-H)2BC8H14}3(PhNH2) (3) was isolated from the reaction of 2 with aniline in diethyl ether. In the formation of these complexes, Ti(IV) is reduced to Ti(III). The coordinated diethyl ether in 2 can be displaced by the stronger bases THF and aniline, to form 1 and 3, respectively. All of the compounds were characterized by single-crystal X-ray diffraction analysis. In complex 1, which contains two coordinated THF ligands, the titanium possesses a 17 electron configuration and there is no evidence for agostic interaction. Complexes 2 and 3 contain only one coordinated ether or aniline ligand, and the titanium possesses a 15 electron configuration. In these compounds, a C-H hydrogen on an alpha carbon on the BC8H14 unit of a 9-BBN hydroborate ligand forms an agostic interaction with the titanium. Criteria for assessing the existence of agostic interactions are discussed. As the potassium salt, the anion of complex 4 is more stable than the complexes 1-3. Organometallic anions of the type [ML4]- for titanium(III) are rare.

Journal Article↗
PubMed2006

Titanium and zirconium complexes of a phosphorus-containing p-tert-butylcalix[5]arene ligand: importance of metal and conformation on ligand/metal binding.

Binding of a calix[5]arene containing a single phosphorus ligand and three hydroxyl groups, calix[5]PNMe2(OH)3, 1, toward titanium and zirconium is investigated to yield insight into the factors that determine the strength of the phosphorus/metal interaction within the constraint of the calix[5]arene. Treatment of 1 with tetrakis(dimethylamino)titanium yields three complexes, 4a, 4b, and 4c, each of which shows the loss of 3 mol of dimethylamine in the reaction with the titanium bound to three oxygens. Treatment of 1 with tetrakis(diethylamino)zirconium proceeds similarly, although only two products, 5a and 5b, were isolated. X-ray structures of the products were obtained. Complexes 4a and 5a show similar geometries, with the calix[5]arene in an approximate cone conformation and the phosphorus lone pair directed toward the metal. The P...M distances are, however, markedly different: 3.69 A in 4a and 3.18 A in 5a, the former indicative of no interaction and the latter a weak one. Complexes 4b and 5b each are dimers, featuring a planar four-membered M-O-M-O ring; however, the titanium is five-coordinate in 4b with no phosphorus/metal bond, while the zirconium in 5b is six-coordinate with a P-Zr distance of 2.95 A. Complex 4c is monomeric with the calix[5]arene in an approximate 1,2-alternate conformation with a P...Ti distance of 2.90 A. The two most significant aspects controlling the phosphorus/metal contact are the metal, with the larger zirconium showing stronger interaction, and the calix[5]arene conformation, with the cone conformation showing the weaker interaction.

Journal Article↗
PubMed2006

Electron deficient carbon-titanium triple bonds: formation of triplet XC/TiX3 methylidyne complexes.

Laser-ablated titanium atoms react with CX4 (X = F and Cl) to produce triplet state XC/TiX3 complexes trapped in an argon matrix. Products are identified by their infrared spectra and comparison to theoretically predicted vibrations. Density functional theory calculations converge to C(3v) symmetry structures for these lowest-energy products. The two unpaired electrons in the carbon 2p orbitals are shared with empty titanium d orbitals leading to degenerate singly occupied pi molecular orbitals and an electron-deficient triple bond between the carbon and titanium centers, on the basis of DFT bonding analysis and spin density calculations. The carbon-titanium distances are near typical C=Ti double bond lengths, and the C-X bonds in the resulting products are shorter than in the CX4 precursors. It appears that X lone-pair conjugation contributes to the C-X bond strength and somewhat to the C-Ti bond, and Cl does better in this regard than F.

Journal Article↗
PubMed2001

Transition-metal-promoted reactions of boron hydrides. 17. Titanium-catalyzed decaborane-olefin hydroborations.

The titanium-catalyzed hydroboration reactions of decaborane with a variety of terminal olefins have been found to result in the exclusive, high-yield formation of monosubstituted decaborane 6-R-B(10)H(13) products, arising from anti-Markovnikov addition of the cage B6-H to the olefin. The titanium-catalyzed reactions are slow, often less than one turnover per hour; however, their high selectivities and yields coupled with the fact that they are simple, one-pot reactions give them significant advantages over the previously reported routes to 6-R-B(10)H(13) compounds. The catalyst also has extended activity with reactions carried out for as long as 13 days, showing little decrease in reactivity, thereby allowing for the production of large amounts of 6-R-B(10)H(13). The titanium-catalyzed reactions of decaborane with the nonconjugated diolefins, 1,5-hexadiene and diallylsilane, were found to give, depending upon reaction conditions and stoichiometries, high yields of either alkenyl-substituted 6-(CH(2)=CH(CH(2))(4))-B(10)H(13) (4) and 6-(CH(2)=CHCH(2)SiMe(2)(CH(2))(3))-B(10)H(13) (5) or linked-cage 6,6'-(CH(2))(6)-(B(10)H(13))(2) (6) and Me(2)Si(6-(CH(2))(3)-B(10)H(13))(2) (7) compounds, respectively. The unique tetra-cage product, Si(6-(CH(2))(3)-B(10)H(13))(4) (8), was obtained by the catalyzed reaction of 4 equiv of decaborane with tetraallylsilane. Sequential use of the titanium catalyst and previously reported platinum catalysts (PtBr(2) or H(2)PtCl(6).6H(2)O with an initiator) provides an efficient pathway to asymmetrically substituted 6-R-9-R'-B(10)H(12) species. The structures of compounds 5, 6, and 8, as well as a platinum derivative, (PSH(+))(2)-commo-Pt-[nido-7-Pt-8-(n-C(8)H(17))B(10)H(11)](2)(2-), of 6-(n-octyl)decaborane have been established by single-crystal crystallographic determinations.

Journal Article↗
PubMed2005

Dynamic behavior of chiral sulfonimidoyl-substituted allyl and alkyl (dimethylamino)titanium(IV) complexes: metallotropic shift, reversible beta-hydride elimination/reinsertion, and ab initio calculations of allyl and alkyl aminosulfoxonium ylides.

Variable-temperature (1)H and (13)C NMR spectroscopy of the sulfonimidoyl-substituted allyltitanium(IV) complexes E-1a-c and Z-1a-c, which carry diethylamino groups at the Ti atom, revealed a fast 1,3-C,N-shift of the Ti atom, leading to an equilibrium between the epimeric Calpha-titanium allyl complexes A and C and the N-titanium allyl aminosulfoxonium ylide B. Based on these findings a model for the reactions of E-1a-c and Z-1a-c with aldehydes is proposed, which features regio- and diastereoselective reactions of the N-titanium ylide B at the alpha-position and the Calpha-titanium complex A at the gamma-position. Model ab initio calculations of the methylene and allyl (dimethylamino)sulfoxonium ylides 10 and 14, respectively, revealed short Calpha-S bonds, a stabilization by both electrostatic interaction and negative hyperconjugation, and a low Calpha-S rotational barrier. The ylides preferentially adopt Calpha-S and Calpha-N conformations in which the lone pair orbital at the Calpha atom is periplanar to the S=O bond and that at the N atom periplanar to the Calpha-Ph bond. Variable-temperature NMR spectroscopy of the sulfonimidoyl-substituted alkyltitanium(IV) complex 16, which carries diethylamino groups at the Ti atom, revealed a dynamic behavior leading to a complete topomerization of all four methylene hydrogens of the Calpha-ethyl groups. Two fast processes are held responsible for the topomerization of the hydrogens of 16. The first one is a reversible intramolecular beta-hydride elimination/alkene-Ti-H insertion with the intermediate formation of a complex between (Et(2)N)TiH and a 1-alkenyl sulfoximine, and the second one consists of a reversible 1,3-C,N-shift of the Ti atom in combination with a Calpha-S bond rotation. Interestingly, the room-temperature NMR spectra of the corresponding sulfonimidoyl-substituted alkyltitanium(IV) complex 17, which carries isopropoxy groups at the Ti atom, give no indication of a similar dynamic behavior of this complex.

Journal Article↗
PubMed2005

Homolysis of weak Ti-O bonds: experimental and theoretical studies of titanium oxygen bonds derived from stable nitroxyl radicals.

Titanium-oxygen bonds derived from stable nitroxyl radicals are remarkably weak and can be homolyzed at 60 degrees C. The strength of these bonds depends sensitively on the ancillary ligation at titanium. Direct measurements of the rate of Ti-O bond homolysis in Ti-TEMPO complexes Cp2TiCl(TEMPO) (3) and Cp2TiCl(4-MeO-TEMPO) (4) (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl, 4-MeO-TEMPO = 2,2,6,6-tetramethyl-4-methoxypiperidine-N-oxyl) were conducted by nitroxyl radical exchange experiments. Eyring plots gave the activation parameters, deltaH++ = 27(+/- 1) kcal/mol, deltaS++ = 6.9(+/- 2.3) eu for 3 and deltaH++ = 28(+/- 1) kcal/mol, deltaS++ = 9.0(+/- 3.0) eu for 4, consistent with a process involving the homolysis of a weak Ti-O bond to generate the transient Cp2Ti(III)Cl and the nitroxyl radical. Thermolysis of the titanocene TEMPO complexes in the presence of epoxides leads to the Cp2Ti(III)Cl-mediated ring-opening of the epoxide followed by trapping by the nitroxyl radical. The X-ray crystal structure of the Ti-TEMPO derivative, Cp2TiCl(4-MeO-TEMPO) (4), is reported. DFT (B3LYP/6-31G*) calculations and experimental studies reveal that the strength of the Ti-O bond decreases dramatically with the number of cyclopentadienyl groups on titanium. The calculated Ti-O bond strength of the monocyclopentadienyl complex 2 is 43 kcal/mol, whereas that of the biscyclopentadienyl complex 3 is 17 kcal/mol, a difference of 26 kcal/mol. These studies reveal that the strength of these Ti-O bonds can be tuned over an interesting and experimentally accessible temperature range by appropriate ligation on titanium.

Journal Article↗