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.