Synthesis, characterization, and reactivity of terminal titanium imido complexes incorporating constrained-geometry carboranyl ligands

Article abstract of DOI:10.1021/om050312g

Reaction of [Me₂C(C₅H₄)(C ₂B₁₀H₁₀)]Li₂ with Ti(=NR)Cl ₂(Py)₃ afforded the corresponding titanium imido complexes [η⁵:σ-Me₂C(C₅H₄)(C ₂B₁₀H₁₀)]Ti(=NR)(Py) (R = ^tBu (1), 2,6-Me₂C₆H₃ (2), 2,6-ⁱPr ₂C₆H₃ (3)). Complexes 2 and 3 were also prepared by an imido exchange reaction of 1 with RNH₂ (R = 2,6-Me₂C₆H₃, 2,6-ⁱPr ₂C₆H₃). Similarly, [η⁵:σ- Me₂C(C₉H₆)(C₂B₁₀H ₁₀)]Ti-(=N^tBu)(Py) (4) was prepared from the reaction of [Me₂C(C₉H₆)(C₂B₁₀H ₁₀)]Li₂ with Ti-(=N^tBu)Cl₂(Py) ₃3. The reactivity of 1 toward a series of unsaturated organic compounds was examined. Complex 1 underwent imido/oxo exchange reactions with carbonyl compounds such as Ph₂CO, PhCHO, and PhNCO to generate the corresponding imines or carbodiimide and oxotitanium oligomers. The resulting insoluble oxotitanium oligomer was trapped by Me₃SiCl, resulting in the formation of a chloride complex, [η⁵:σ-Me ₂C(C₅H₄)(C₂B₁₀H ₁₀)]Ti-(OSiMe₃)Cl (5). Interaction of 1 with CS ₂ gave ^tBuN=C=N^tBu and ^tBuN=C=S with a molar ratio of 1:3 as well as an insoluble sulfidotitanium complex. 1 was able to catalyze the hydroamination of phenyl acetylene with amines to afford both Markovnikov and antiMarkovnikov products. The product ratio was dependent upon the steric hindrance of the amines used. High regioselectivity was observed for sterically demanding amines such as t-BuNH₂. The anti-Markovnikov [2+2] cycloaddition intermediate [η⁵:σ- Me₂C(C₅H₄)(C₂B₁₀H ₁₀)]-Ti(η³-N^tBuCH=CPh) (6) was successfully isolated from a stoichiometric reaction of 1 with phenyl acetylene in toluene. The molecular structures of 3-6 were further confirmed by single-crystal X-ray analyses.