Synthesis and Structure of Bifunctional Zirconocene/Borane Complexes and Their Activation for Ethylene Polymerization

The potassium salt of 1 was transmetalated by reaction with (Cp-allyl)­ZrCl3(dme), yielding the complex (NC-nacnac)­Cp-allylZrCl2 (2). Addition of 1 molar equiv of B­(C6F5)3 gave [(C6F5)3B-NC-nacnac]­Cp-allylZrCl2 (3), and the subsequent addition of 1 molar equiv of HB­(C6F5)2 to 3 gave the hydroborated species [((C6F5)3B-NC-nacnac)­Cp-(CH2)3-B­(C6F5)2]­ZrCl2 (4). The hydroboration of 2 with 1 molar equiv of HB­(C6F5)2 gave an insoluble product. This product was fully characterized by 11B and 13C solid-state NMR and IR, which showed that the hydroboration followed by intermolecular adduct formation (R–B­(C6F5)2- - -NC- - -R′) occurs, resulting in an organometallic polymer (5). In addition to the CN-free [nacnac]­Cp-allylZrCl2 (6), the hydroborated derivative [(nacnac)­Cp-(CH2)3-B­(C6F5)2] (7) was also prepared. Complexes 2–7 were activated with methylaluminoxane (MAO) and gave active catalysts for ethylene polymerization. The polymers produced were linear and had high molecular weight, with polydispersities (PDI) of less than 2, indicating that the catalysts are single site. The presence of the allyl group on the Cp ring was found to increase the molecular weight of the materials produced. In addition to discrete complexes, an organometallic polymer (5) was formed. This compound is air stable and, while not very soluble, polymerizes ethylene with good activity.