Synthesis of a [(π-Cyano-nacnac)Cp]zirconium Complex and Its Remote Activation for Ethylene Polymerization

The NC-nacnacH ligand (2) was prepared by the deprotonation of the unsymmetrically N5-phenyl, N1-2,6-diisopropylphenyl substituted bis(imino) acetylacetonate nacnacH system (1) with n-butyllithium followed by cyanation with tosyl cyanide. Subsequent deprotonation (KH) gave the [NC-nacnac]K salt (3), which was transmetalated by reacting it with CpZrCl3(dme), to yield the complex (NC-nacnac)CpZrCl2 (5). Addition of one molar equivalent of B(C6F5)3 gave [(C6F5)3B-NC-nacnac]CpZrCl2 (6). The compounds 2, 5, and 6 were characterized by X-ray diffraction. Activation of 5 with MAO gave an active homogeneous Ziegler−Natta catalyst for ethylene polymerization. The (NC-nacnac)CpZrCl2/MAO system is ca. 7 times more active than the CN-free reference system (nacnac)CpZrCl2 (4)/MAO. The B(C6F5)3-containing system 6/MAO has an activity similar to 5/MAO but allows for much lower MAO concentration before the catalytic activity ceases.