Preparation, Structure, and Ethylene (Co)Polymerization Behavior of Group IV Metal Complexes with an [OSSO]-Carborane Ligand

The synthesis of Group IV metal complexes that contain a tetradentate dianionic [OSSO]-carborane ligand [(HOC(6)H(2)tBu(2)-4,6)(2)(CH2)(2)S2C2-(B10H10)] (1a) is described. Reactions of TiCl4 and Ti(OiPr)(4) with the [OSSO]-type ligand 1a afford six-coordinated titanium complex [Ti(OC(6)H(2)tBu(2)-4,6)(2)(CH2)(2)S2C2-(B10H10)Cl-2] (2a) and four-coordinated titanium complex [Ti(OC(6)H(2)tBu(2)-4,6)(2)-(CH2)(2)S2C2(B10H10)(OiPr)(2)] (2b), respectively. ZrCl4 and HfCl4 were treated with 1a to give six-coordinated zirconium complex [Zr(OC(6)H(2)tBu(2)-4,6)(2)-(CH2)(2)S2C2(B10H10)Cl-2(thf)(2)] (2c) and six-coordinated hafnium complex [Hf(OC(6)H(2)tBu(2)-4,6)(2)(CH2)(2)S2C2-(B10H10)Cl-2] (2d). All the complexes were fully characterized by IR, NMR spectroscopy, and elemental analysis. In addition, X-ray structure analyses were performed on complexes 2a and 2b and reveal the expected different coordination geometry due to steric hindrance effects. Extended X-ray absorption fine structure (EXAFS) spectroscopy was performed on complexes 2c and 2d to describe the coordination chemistry of this ligand around Zr and Hf. Six-coordinated titanium complex 2a showed good activity toward ethylene polymerization as well as toward copolymerization of ethylene with 1-hexene in the presence of methylaluminoxane (MAO) as cocatalyst (up to 1060 kg[mol(Ti)](-1)h(-1) in the case of 10 atm of ethylene pressure).