Synthesis, Structure, and Olefin Polymerization Behavior of Constrained-Geometry Group 4 Metallacarboranes Incorporating Imido-Dicarbollyl Ligands

New imido-carboranes 1-(CHNC6H3R2-2,6)-1,2-C2B10H11 (R = iPr (3a), Me (3b)) were successfully prepared by Schiff base condensation of 1-CHO-1,2-C2B10H11 with R2C6H3NH2. They were readily converted into the corresponding imido-dicarbollyl ligands 7-(CHNHC6H3R2-2,6)-7,8-C2B9H11 (R = iPr (4a), Me (4b)) by refluxing in dry MeOH. Treatment of 3a with Ti(NMe2)4 in hot toluene gave a constrained-geometry complex, [η1:η5-(iPr2C6H3NCH)C2B9H10]Ti(NMe2)2 (5a). Under the same reaction conditions, interaction of 3b with Ti(NMe2)4 produced a mixture of [η1:η5-(Me2C6H3NCH)C2B9H10]Ti(NMe2)2 (5b) and [η1:η5-(Me2N)CH(NMe2)(C2B9H10)Ti(NMe2)2 (8). Reaction of 4a with M(NMe2)4 in toluene/DME at room temperature afforded 5a and [η1:η5-(iPr2C6H3NCH)C2B9H10]M(NMe2)2(NHMe2) (M = Zr (6a), Hf (7a)), respectively. Complexes 5a, 6a, and 7a were active catalysts for the polymerization of ethylene in the presence of MMAO with activities of 3−16 kg/mol·h·atm. These new complexes were fully characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 3a, 3b, 4a, 5a, 5b, 6a, 7a, and 8 were further confirmed by single-crystal X-ray analyses.