Synthesis, Characterization, and Reactivity of Terminal Titanium Imido Complexes Incorporating Constrained-Geometry Carboranyl Ligands

Reaction of [Me2C(C5H4)(C2B10H10)]Li2 with Ti(NR)Cl2(Py)3 afforded the corresponding titanium imido complexes [η5:σ-Me2C(C5H4)(C2B10H10)]Ti(NR)(Py) (R = tBu (1), 2,6-Me2C6H3 (2), 2,6-iPr2C6H3 (3)). Complexes 2 and 3 were also prepared by an imido exchange reaction of 1 with RNH2 (R = 2,6-Me2C6H3, 2,6-iPr2C6H3). Similarly, [η5:σ-Me2C(C9H6)(C2B10H10)]Ti(NtBu)(Py) (4) was prepared from the reaction of [Me2C(C9H6)(C2B10H10)]Li2 with Ti(NtBu)Cl2(Py)3. 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-Me2C(C5H4)(C2B10H10)]Ti(OSiMe3)Cl (5). Interaction of 1 with CS2 gave tBuNCNtBu 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 anti-Markovnikov 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)(C2B10H10)]Ti(η3-NtBuCH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.