Titanium and Zirconium Et2C2B4H4−Metal−Phosphine Complexes: Synthesis, Characterization, and Ethylene Polymerization Activity1

The synthesis, structures, and reactivity of a series of 14-electron complexes including L2Cl2Ti(Et2C2B4H4) (1−3, L2 = 2 PMe3, Me2P(CH2)2PMe2, or Me2P(CH2)3PMe2], [Me2P(CH2)3PMe2]2Me2Ti(Et2C2B4H4) (22), and related compounds are reported together with the preparation and spectroscopic characterization of the analogous zirconium species L2Cl2Zr(Et2C2B4H4) (L2 = 2PMe3 or Me2P(CH2)3PMe2 (24 and 25). Compounds 1−3, 22, and 25 are catalyst precursors for the polymerization of ethylene at 1 atm pressure in the presence of methylaluminoxane, thus extending Ziegler−Natta chemistry for the first time to complexes of the [R2C2B4H4]2- small carborane ligands. Although the choice of phosphine ligand has a dramatic effect on catalyst activity, NMR data reveal aluminum−phosphine binding under conditions approximating the catalytic mixtures for the PMe3 and Me2P(CH2)2PMe2 (dmpe) systems, whereas the state of Me2P(CH2)3PMe2 (dmpp) coordination is not clear. Multiple catalyst species are probably active in these reaction ...