A Bridging bis-Allyl Titanium Complex: Mechanistic Insights into the Electronic Structure and Reactivity.

Treatment of the dinuclear compound [{Ti(η5-C5Me5)Cl2}2(µ-O)] with allylmagnesium chloride provides the formation of the allyltitanium(III) derivative [{Ti(η5-C5Me5)(µ-C3H5)}2(µ-O)] (1), structurally identified by single-crystal X-ray analysis. Density functional theory (DFT) calculations confirm that the electronic structure of 1 is a singlet state, and the molecular orbital analysis, along with the short Ti-Ti distance, reveal the presence of a metal-metal single bond between the two Ti(III) centers. Complex 1 reacts rapidly with organic azides, RN3 (R = Ph, SiMe3), to yield the allyl µ-imido derivatives [{Ti(η5-C5Me5)(CH2CH═CH2)2}2(µ-NR)(µ-O)] [R = Ph(2), SiMe3(3)] along with molecular nitrogen release. Reaction of 2 and 3 with H2 leads to the µ-imido propyl species [{Ti(η5-C5Me5)(CH2CH2CH3)2}2(µ-NR)(µ-O)] [R = Ph(4), SiMe3(5)]. Theoretical calculations were used to gain insight into the hydrogenation mechanism of complex 3 and rationalize the lower reactivity of 2. Initially, the µ-imido bridging group in these complexes activates the H2 molecule via addition to the Ti-N bonds. Subsequently, the titanium hydride intermediates induce a change in hapticity of the allyl ligands, and the nucleophilic attack of the hydride to the allyl groups leads to metallacyclopropane intermediates. Finally, the proton transfer from the amido group to the metallacyclopropane moieties affords the propyl complexes 4 and 5.

Enhanced solubilisation of six PAHs by three synthetic cyclodextrins for remediation applications: molecular modelling of the inclusion complexes.

Solubilisation of six polycyclic aromatic hydrocarbons (PAHs) (acenaphthene, anthracene, fluoranthene, fluorene, phenanthrene and pyrene) by three synthetic cyclodextrins (CDs) (2-hydroxypropyl-ß-CD, hydroxypropyl-γ-CD and randomly methylated-ß-CD) was investigated in order to select the CD which presents the greatest increase in solubility and better complexation parameters for its use in contaminated scenarios. The presence of the three cyclodextrins greatly enhanced the apparent water solubility of all the PAHs through the formation of inclusion complexes of 1:1 stoichiometry. Anthracene, fluoranthene, fluorene and phenanthrene clearly presented a higher solubility when ß-CD derivatives were used, and especially the complexes with the randomly methylated-ß-CD were favoured. On the contrary, pyrene presented its best solubility results when using 2-hydroxypropyl-γ-CD, but for acenaphthene the use of any of the three CDs gave the same results. Complementary to experimental phase-solubility studies, a more in-depth estimation of the inclusion process for the different complexes was carried out using molecular modelling in order to find a correlation between the degree of solubilisation and the fit of PAH molecules within the cavity of the different CDs and to know the predominant driving forces of the complexation.

Co-complexation of lithium gallates on the titanium molecular oxide {[Ti(η5-C5Me5)(µ-O)}3(µ3-CH)].

Amide and lithium aryloxide gallates [Li(+){RGaPh(3)}(-)] (R = NMe(2), O-2,6-Me(2)C(6)H(3)) react with the µ(3)-alkylidyne oxoderivative ligand [{Ti(η(5)-C(5)Me(5))(µ-O)}(3)(µ(3)-CH)] (1) to afford the gallium-lithium-titanium cubane complexes [{Ph(3)Ga(µ-R)Li}{Ti(η(5)-C(5)Me(5))(µ-O)}(3)(µ(3)-CH)] [R = NMe(2) (3), O-2,6-Me(2)C(6)H(3) (4)]. The same complexes can be obtained by treatment of the [Ph(3)Ga(µ(3)-O)(3){Ti(η(5)-C(5)Me(5))}(3)(µ(3)-CH)] (2) adduct with the corresponding lithium amide or aryloxide, respectively. Complex 3 evolves with formation of 5 as a solvent-separated ion pair constituted by the lithium dicubane cationic species [Li{(µ(3)-O)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-CH)}(2)](+) together with the anionic [(GaPh(3))(2)(µ-NMe(2))](-) unit. On the other hand, the reaction of 1 with Li(p-MeC(6)H(4)) and GaPh(3) leads to the complex [Li{(µ(3)-O)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-CH)}(2)][GaLi(p-MeC(6)H(4))(2)Ph(3)] (6). X-ray diffraction studies were performed on 1, 2, 4, and 5, while trials to obtain crystals of 6 led to characterization of [Li{(µ(3)-O)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-CH)}(2)][PhLi(µ-C(6)H(5))(2)Ga(p-MeC(6)H(4))Ph] 6a.