Synthesis, Structural Characterization, and Olefin Polymerization Behavior of Group 4 Metal Complexes with Constrained-Geometry Carborane Ligands

Abstract

Several new group 4 metal amide complexes with recently developed constrained-geometry carborane ligands, [η5:σ-Me2A(C9H6)(C2B10H10)]M(NR2)2 and [η5:σ-Me2A(C5H4)(C2B10H10)]M(NR2)2 (A = C, Si; M = Ti, Zr; R = Me, Et), were prepared in good yield via amine elimination reactions of M(NR2)4 and the corresponding neutral ligands in toluene. Treatment of the amide complexes with 2.5 equiv of Me2NH·HCl or Me3N·HCl led to high yields of the corresponding chloride complexes, [{η5:σ-Me2A(C9H6)(C2B10H10)}ZrCl(μ-Cl)1.5]2- (A = C, Si), which could also be prepared from an equimolar reaction between ZrCl4(THF)2 and [Me2C(C9H6)(C2B10H10)]Li2. In contrast, excess Me3SiCl could only convert [η5:σ-Me2C(C5H4)(C2B10H10)]Ti(NMe2)2 to [η5:σ-Me2C(C5H4)(C2B10H10)]TiCl(NMe2), due to steric effects. All these new complexes have been fully characterized by 1H, 13C, and 11B NMR and IR spectroscopic data and elemental analyses. Thirteen out of fourteen newly prepared complexes have been structurally characterized by single-crystal X-ray diffraction studies. The chloride complexes exhibit a very high ethylene polymerization activity when they are activated with MMAO.