Synthesis and Structure of Titanium(III) Bis(decamethyltitanocene) Oxide

Reactions of permethyltitanocene tucked-in derivatives with carbon dioxide

Both single tucked-in permethyltitanocene 1 and double tucked-in permethyltitanocene 2 react with excess CO₂ by insertion into their Ti-CH₂ bonds. The former one precipitates instantly a yellow carboxylate-tethered oligomer [3]_n which is insoluble in aprotic solvents and in a vacuum it sublimes as a monomer without decomposition. Computations for n ≤ 4 optimised the structure of the monomer [3] and showed that open chain oligomers bound by dative O → Ti bonds were not sterically hindered. The latter bond dissociates when [3]_n is oxidized by chlorination with CDCl₃ or CD₂Cl₂ to give Ti(IV) chloride 4 or upon metathesis of [3]_n with Me₃SiCl yielding Ti(III) chloride 5. Oxidative addition of MeCN affords a C-C coupled dinuclear titanocene diimine 6. Compound [3]_n also reacts with 1 to give the tethered carbodiolate 8 or with [Cp*₂TiH] (where Cp* = η⁵-C₅Me₅) to give the half-tethered carbodiolate 10. The non-tethered carbodiolate 12 was obtained from [Cp*₂TiH] and CO₂ yielding titanocene formate by reaction of the latter with another equivalent of [Cp*₂TiH]. All these carbodiolates contain Ti(III) metal atoms forming electronic triplet states of axial or orthorhombic symmetry. In contrast to the rapidly reacting 1 compound 2 reacts with excess CO₂ slowly in m-xylene at 100 °C using only one of its two Ti-CH₂ moieties. The structure of the obtained carbodiolate 13 indicates that the primary product analogous to 3 reacts with 2 more rapidly than with CO₂.

Electronic Structure Analysis and Reactivity of the Bimetallic Bis-Titanocene Vinylcarboxylate Complex, [(Cp2Ti)2(O2C3TMS2)]†

Multimetallic redox cooperativity features heavily in both bioinorganic and synthetic reactions. Here, the electronic structure of the bimetallic Ti/Ti complex 11, [(Cp₂Ti)₂(O₂C₃TMS₂)] has been revisited with EPR, confirming a predominantly Ti^III/Ti^III electronic structure. Reactions of 11 with 2,6-dimethylphenyl isocyanide (CNXyl), TMSCl, MeI, and BnCl were explored, revealing differential redox chemistry of the bimetallic core. In reactions with CNXyl and TMSCl, the metallacyclic Ti^III center remained unperturbed, with reactions taking place at the pendent κ²(O,O)-titanocene fragment, while reaction with MeI resulted in remote oxidation of the metallacyclic Ti center, indicative of a cooperative redox process. All structures were studied via X-ray diffraction and EPR spectroscopic analysis, and their electronic structures are discussed in the context of the covalent bond classification (CBC) electron counting method.

Ground Triplet Spirobiradical: 2,2',7,7'-Tetra( tert-butyl)-9,9'(10 H,10' H)-spirobiacridine-10,10'-dioxyl

A new spirobiradical, 2,2',7,7'-tetra( tert-butyl)-9,9'(10 H,10' H)-spirobiacridine-10,10'-dioxyl, was prepared. The crystallographic analysis clarified the D_{2 d} molecular structure, suggesting the degeneracy of SOMOs. The magnetic study revealed that intramolecular ferromagnetic coupling was operative with 2 J/ k_B = +23(1) K. To the best of our knowledge, the ferromagnetic coupling parameter is the largest ever reported for a paramagnetic spiro compound.

Hydrogenation of titanocene and zirconocene bis(trimethylsilyl)acetylene complexes

Reactions following the addition of dihydrogen under maximum atmospheric pressure to bis(trimethylsilyl)acetylene (BTMSA) complexes of titanocenes, [(η5-C5H5-nMen)2Ti(η2-BTMSA)] (n = 0, 1, 3, and 4) (1A-1D), and zirconocenes, [(η5-C5H5-nMen)2Zr(η2-BTMSA)] (n = 2-5) (4A-4D), proceeded in diverse ways and, depending on the metal, afforded different products. The former complexes lost, in all cases, their BTMSA ligand via its hydrogenation to bis-1,2-(trimethylsilyl)ethane when reacted at 80 °C for a prolonged reaction time. For n = 0, 1, and 3, the titanocene species formed in situ dimerised via the formation of fulvalene ligands and two bridging hydride ligands, giving known green dimeric titanocenes (2A-2C). For n = 4, a titanocene hydride [(η5-C5HMe4)2TiH] (2D) was formed, similarly to the known [(η5-C5Me5)2TiH] (2E) for n = 5; however, in contrast to this example, 2D in the absence of dihydrogen spontaneously dehydrogenated to the known Ti(iii)-Ti(iii) dehydro-dimer [{Ti(η5-C5HMe4)(μ-η1:η5-C5Me4)}2] (3B). This complex has now been fully characterised via spectroscopic methods, and was shown through EPR spectroscopy to attain an intramolecular electronic triplet state. The zirconocene-BTMSA complexes 4A-4D reacted uniformly with one hydrogen molecule to give Zr(iv) zirconocene hydride alkenyls, [(η5-C5H5-nMen)2ZrH{C(SiMe3)[double bond, length as m-dash]CH(SiMe3)}] (n = 2-5) (5A-5D). These were identified through their 1H and 13C NMR spectra, which show features typical of an agostically bonded proton, [double bond, length as m-dash]CH(SiMe3). Compounds 5A-5D formed equilibria with the BTMSA complexes 4A-4D depending on hydrogen pressure and temperature.

Functionalized Sugarcane Bagasse for U(VI) Adsorption from Acid and Alkaline Conditions

The highly efficient removal of uranium from mine tailings effluent, radioactive wastewater and enrichment from seawater is of great significance for the development of nuclear industry. In this work, we prepared an efficient U(VI) adsorbent by EDTA modified sugarcane bagasse (MESB) with a simple process. The prepared adsorbent preserves high adsorptive capacity for UO22+ (pH 3.0) and uranyl complexes, such as UO2(OH)+, (UO2)2(OH)22+ and (UO2)3(OH)5+ (pH 4.0 and pH 5.0) and good repeatability in acidic environment. The maximum adsorption capacity for U(VI) at pH 3.0, 4.0 and 5.0 is 578.0, 925.9 and 1394.1 mg/g and the adsorption capacity loss is only 7% after five cycles. With the pH from 3.0 to 5.0, the inhibitive effects of Na+ and K+ decreased but increased of Mg2+ and Ca2+. MESB also exhibits good adsorption for [UO2(CO3)3]4- at pH 8.3 from 10 mg/L to 3.3 μg/L. Moreover, MESB could effectively extract U(VI) from simulated seawater in the presence of other metals ions. This work provided a general and efficient uranyl enriched material for nuclear industry.

Decamethyltitanocene hydride intermediates in the hydrogenation of the corresponding titanocene-(η2-ethene) or (η2-alkyne) complexes and the effects of bulkier auxiliary ligands

¹H NMR studies of reactions of titanocene [Cp*₂Ti] (Cp* = η⁵-C₅Me₅) and its derivatives [Cp*(η⁵:η¹-C₅Me₄CH₂)TiMe] and [Cp*₂Ti(η²-CH₂[double bond, length as m-dash]CH₂)] with excess dihydrogen at room temperature and pressures lower than 1 bar revealed the formation of dihydride [Cp*₂TiH₂] (1) and the concurrent liberation of either methane or ethane, depending on the organometallic reactant. The subsequent slow decay of 1 yielding [Cp*₂TiH] (2) was mediated by titanocene formed in situ and controlled by hydrogen pressure. The crystalline products obtained by evaporating a hexane solution of fresh [Cp*₂Ti] in the presence of hydrogen contained crystals having either two independent molecules of 1 in the asymmetric part of the unit cell or cocrystals consisting of 1 and [Cp*₂Ti] in a 2 : 1 ratio. Hydrogenation of alkyne complexes [Cp*₂Ti(η²-R¹C[triple bond, length as m-dash]CR²)] (R¹ = R² = Me or Et) performed at room temperature afforded alkanes R¹CH₂CH₂R², and after removing hydrogen, 2 was formed in quantitative yields. For alkyne complexes containing bulkier substituent(s) R¹ = Me or Ph, R² = SiMe₃, and R¹ = R² = Ph or SiMe₃, successful hydrogenation required the application of increased temperatures (70-80 °C) and prolonged reaction times, in particular for bis(trimethylsilyl)acetylene. Under these conditions, no transient 1 was detected during the formation of 2. The bulkier auxiliary ligands η⁵-C₅Me₄^tBu and η⁵-C₅Me₄SiMe₃ did not hinder the addition of dihydrogen to the corresponding titanocenes [(η⁵-C₅Me₄^tBu)₂Ti] and [(η⁵-C₅Me₄SiMe₃)₂Ti] yielding [(η⁵-C₅Me₄^tBu)₂TiH₂] (3) and [(η⁵-C₅Me₄SiMe₃)₂TiH₂] (4), respectively. In contrast to 1, the dihydride 4 did not decay with the formation of titanocene monohydride, but dissociated to titanocene upon dihydrogen removal. The monohydrides [(η⁵-C₅Me₄^tBu)₂TiH] (5) and [(η⁵-C₅Me₄SiMe₃)₂TiH] (6) were obtained by insertion of dihydrogen into the intramolecular titanium-methylene σ-bond in compounds [(η⁵-C₅Me₄^tBu)(η⁵:η¹-C₅Me₄CMe₂CH₂)Ti] and [(η⁵-C₅Me₄SiMe₃)(η⁵:η¹-C₅Me₄SiMe₂CH₂)Ti], respectively. The steric influence of the auxiliary ligands became clear from the nature of the products obtained by reacting 5 and 6 with butadiene. They appeared to be the exclusively σ-bonded η¹-but-2-enyl titanocenes (7) and (8), instead of the common π-bonded derivatives formed for the sterically less congested titanocenes, including [Cp*₂Ti(η³-(1-methylallyl))] (9). The molecular structure optimized by DFT for compound 1 acquired a distinctly lower total energy than the analogously optimized complex with a coordinated dihydrogen [Cp*₂Ti(η²-H₂)]. The stabilization energies of binding the hydride ligands to the bent titanocenes were estimated from counterpoise computations; they showed a decrease in the order 1 (-132.70 kJ mol^-1), 3 (-121.11 kJ mol^-1), and 4 (-112.35 kJ mol^-1), in accordance with the more facile dihydrogen dissociation.

Highly selective visible light-induced Ti–O bond splitting in an ansa-titanocene dihydroxido complex

Visible light irradiation of an ansa-titanocene(iv) dihydroxido complex Me₄Si₂(C₅Me₄)₂Ti(OH)₂ induces highly selective Ti–O bond activation to exclusively yield Ti(iii) complexes.