Remote carbon−hydrogen activation on titanium dinuclear complexes [{Ti(η 5 -C 5 Me 5 )R 2 } 2 (μ-O)] [R = CH 2 SiMe 3 2, CH 2 CMe 3 3, and CH 2 Ph 5) have been examined both synthetically and theoretically. While the thermal treatment of the oxoderivative [{Ti(η 5 -C 5 Me 5 )(CH 2 SiMe 3 ) 2 } 2 (μ-O)] (2) led to a series of metallacycle complexes (2a−c) by sequential carbon−hydrogen activation processes, [{Ti(η 5 -C 5 Me 5 )(CH 2 CMe 3 ) 2 } 2 (μ-O)] (3) gave rise to the formation of the metallacycle tuck-over species [Ti 2 (η 5 -C 5 Me 5 )(μ-η 5 -C 5 Me 4 CH 2 -κC)(CH 2 CMe 3 )(μ-CH 2 CMe 2 CH 2 )(μ-O)] (4), as result of hydrogen abstraction from a η 5 -C 5 Me 5 ligand. However, the thermolysis of the tetrabenzyl complex [{Ti(η 5 -C 5 Me 5 )(CH 2 Ph) 2 } 2 (μ-O)] (5) yielded the derivative [Ti 2 (η 5 -C 5 Me 5 )(μ-η 5 -C 5 Me 4 CH 2 -κC)(CH 2 Ph) 3 (μ-O)] ( 6) that only exhibits tuck-over η 5 -C 5 Me 5 metalation. DFT calculations show that the mechanism involves a first α-hydrogen abstraction to generate a transient titanium alkylidene, which enables it to activate βand γ-C(sp 3 )-H bonds on the adjacent titanium center. The calculations also establish a reactivity order for the different type of γ-H abstractions, trimethylsilyl > neopentyl ≌ benzyl, allowing us to explain the observed selectivity.

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.

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The reactivity of the "tuck-over" species [Ti2( 5 -C5Me5)(CH2Ph)3(- 5 -C5Me4CH2-C)(-O)] ( 1) and [Ti2((2) towards isocyanides has been examined both synthetically and theoretically. Treatment of 1 with the isocyanides RNC, R = Me3SiCH2, 2,6-Me2C6H3, tBu, iPr, leds to a series of  2 -iminoacyl species (3-6) where the molecule of isocyanide inserts into one of the terminal metal-alkyl bonds. The analogous reaction of the "tuck-over" metallacycle species 2 with 2,6-Me2C6H3NC and tBuNC results in the initial insertion of one isocyanide into the terminal Ti-alkyl bond to form the iminoacyl complexes 7 and 8, followed by a second insertion into the metallacycle moiety to generate 9, in the case of tert-butylisocyanide. DFT calculations support the selective reactivity observed experimentally with a kinetic and thermodynamic preference for RNC insertion on the terminal alkyl groups bound to both metallic centers over the alternative insertion on the "tuck-over" ligand.

Treatment of the dinuclear compound [{Ti( 5 -C5Me5)Cl2}2(-O)] with allylmagnesium chloride provides the formation of the allyltitanium(III) derivative [{Ti( 5 -C5Me5)(-C3H5)}2(-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 -imido derivatives3)] along with molecular nitrogen release. Reaction of 2 and 3 with H2 leads to the -imido propyl species [{Ti( 5 -C5Me5)(CH2CH2CH3)}2(-NR)(-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 -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 hydride to the allyl groups leads to metallacyclopropane intermediates. Finally, the proton transfer from the amido group to the metallacyclopropane moieties afford the propyl complexes 4 and 5.