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Functionalization of Complexed N₂O in Bis(pentamethylcyclopentadienyl) Systems of Zirconium and Titanium.

ABSTRACT: Methyl triflate reacts with the metastable azoxymetallacyclopentene complex Cp*₂Zr(N(O)NCPhCPh), generated in situ from nitrous oxide insertion into the Zr-C bond of Cp*₂Zr(?²-PhCCPh) at -78 °C, to afford the salt [Cp*₂Zr(N(O)N(Me)CPhCPh)][O₃SCF₃] (1) in 48% isolated yield. A single-crystal X-ray structure of 1 features a planar azoxymetallacycle with methyl alkylation taking place only at the ?-nitrogen position of the former Zr(N(O)NCPhCPh) scaffold. In addition to 1, the methoxy-triflato complex Cp*₂Zr(OMe)(O₃SCF₃) (2) was also isolated from the reaction mixture in 26% yield and fully characterized, including its independent synthesis from the alkylation of Cp*₂Zr=O(NC₅H₅) with MeO₃SCF₃. Complex 2 could also be observed, spectroscopically, from the thermolysis of 1 (80 °C, 2 days). In contrast to Cp*₂Zr(N(O)NPhCCPh), the more stable titanium N₂O-inserted analogue, Cp*₂Ti(N(O)NCPhCPh), reacts with MeO₃SCF₃ to afford a 1:1 mixture of regioisomeric salts, [Cp*₂Ti(N(O)N(Me)CPhCPh)][O₃SCF₃] (3) and [Cp*₂Ti(N(OMe)NCPhCPh)][O₃SCF₃] (4), in a combined 65% isolated yield. Single-crystal X-ray diffraction studies of a cocrystal of 3 and 4 show a 1:1 mixture of azoxymetallacyle salts resulting from methyl alkylation at both the ?-nitrogen and the ?-oxygen of the former Ti(N(O)NCPhCPh ring. As opposed to alkylation reactions, the one-electron reduction of Cp*₂Ti(N(O)NCPhCPh) with KC₈, followed by encapsulation with the cryptand 2,2,2-Kryptofix, resulted in the isolation of the discrete radical anion [K(2,2,2-Kryptofix)][Cp*₂Ti(N(O)NCPhCPh)] (5) in 68% yield. Complex 5 was studied by single-crystal X-ray diffraction, and its solution X-band EPR spectrum suggested a nonbonding ?-type wedge hybrid orbital on titanium, d(z²)/d(x²-y²), houses the unpaired electron, without perturbing the azoxymetallacycle core in Cp*₂Ti(N(O)NCPhCPh). Theoretical studies of Ti and the Zr analogue are also presented and discussed.

SUBMITTER: Mindiola DJ

PROVIDER: S-EPMC4059529 | biostudies-literature | 2014 Jun

REPOSITORIES: biostudies-literature

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Functionalization of Complexed N2O in Bis(pentamethylcyclopentadienyl) Systems of Zirconium and Titanium.

Mindiola Daniel J DJ Watson Lori A LA Meyer Karsten K Hillhouse Gregory L GL

Organometallics 20140522 11

Methyl triflate reacts with the metastable azoxymetallacyclopentene complex Cp*2Zr(N(O)NCPhCPh), generated in situ from nitrous oxide insertion into the Zr-C bond of Cp*2Zr(η2-PhCCPh) at -78 °C, to afford the salt [Cp*2Zr(N(O)N(Me)CPhCPh)][O3SCF3] (1) in 48% isolated yield. A single-crystal X-ray structure of 1 features a planar azoxymetallacycle with methyl alkylation taking place only at the β-nitrogen posit ...[more]

PMID: 24954968

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Project description:Orthopedic implant failure due to aseptic loosening and mechanical instability remains a major problem in total joint replacement. Improving osseointegration at the bone-implant interface may reduce micromotion and loosening. Bone sialoprotein (BSP) has been shown to enhance bone formation when coated onto titanium femoral implants and in rat calvarial defect models. However, the most appropriate method of BSP coating, the necessary level of BSP coating, and the effect of BSP coating on cell behavior remain largely unknown. In this study, BSP was covalently coupled to titanium surfaces via an aminosilane linker (APTES), and its properties were compared to BSP applied to titanium via physisorption and untreated titanium. Cell functions were examined using primary human osteoblasts (hOBs) and L929 mouse fibroblasts. Gene expression of specific bone turnover markers at the RNA level was detected at different intervals. Cell adhesion to titanium surfaces treated with BSP via physisorption was not significantly different from that of untreated titanium at any time point, whereas BSP application via covalent coupling caused reduced cell adhesion during the first few hours in culture. Cell migration was increased on titanium disks that were treated with higher concentrations of BSP solution, independent of the coating method. During the early phases of hOB proliferation, a suppressive effect of BSP was observed independent of its concentration, particularly when BSP was applied to the titanium surface via physisorption. Although alkaline phosphatase activity was reduced in the BSP-coated titanium groups after 4 days in culture, increased calcium deposition was observed after 21 days. In particular, the gene expression level of RUNX2 was upregulated by BSP. The increase in calcium deposition and the stimulation of cell differentiation induced by BSP highlight its potential as a surface modifier that could enhance the osseointegration of orthopedic implants. Both physisorption and covalent coupling of BSP are similarly effective, feasible methods, although a higher BSP concentration is recommended.

Project description:BACKGROUND:The aim of this study was to compare the 5-year survival and success rates of 3.3 mm dental implants either made from titanium-zirconium (TiZr) alloy or from Grade IV titanium (Ti Grade IV) in mandibular implant-based removable overdentures. METHODS:The core study had a follow-up period of 36 months and was designed as a randomized, controlled, double-blind, split-mouth multicenter clinical trial. Patients with edentulous mandibles received two Straumann Bone Level implants (diameter 3.3 mm, SLActive®), one of TiZr (test) and one of Ti Grade IV (control), in the interforaminal region. This follow-up study recruited patients from the core study and evaluated the plaque and sulcus bleeding indices, radiographic crestal bone level, as well as implant survival and success 60 months after implant placement. RESULTS:Of the 91 patients who initially received implants, 75 completed the 36 month follow-up and 49 were available for the 60 month examination. Two patients were excluded so that a total of 47 patients with an average age of 72?±?8 years were analysed. The characteristics and 36-month performance of the present study cohort did not differ from the non-included initial participants (p?>?0.05). In the period since the 36-month follow-up examination, no implant was lost. The cumulative implant survival rate was 98.9 % for the TiZr group and 97.8 % for the Ti Grade IV group. Crestal bone level changes at 60 months were not different in the test and control group (TiZr -0.60?±?0.69 mm and Ti Grade IV -0.61?±?0.83 mm; p?=?0.96). The cumulative implant success rate after 60 months was 95.8 and 92.6 % for TiZr and Ti Grade IV, respectively. CONCLUSIONS:After 60 months, the positive outcomes of the 36 month results for TiZr and Ti Grade IV implants were confirmed, with no significant differences with regard to crestal bone level change, clinical parameters and survival or success rates. TiZr implants performed equally well compared to conventional Ti Grade IV 3.3 mm diameter-reduced implants for mandibular removable overdentures. TRIAL REGISTRATION:Registered on www.clinicaltrials.gov: NCT01878331.

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Functionalization of Complexed N₂O in Bis(pentamethylcyclopentadienyl) Systems of Zirconium and Titanium.

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Functionalization of Complexed N<sub>2</sub>O in Bis(pentamethylcyclopentadienyl) Systems of Zirconium and Titanium.

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