Dinuclear Half-Titanocene Complex Bearing an Anthracene-Bridged Bifunctional Alkoxide Ligand: Unprecedented Cooperativity toward Copolymerization of Ethylene with 1-Octene or Norbornene

Dinuclear half-titanocene complex Ti2 bearing an anthracene-bridged bifunctional alkoxide ligand (LH2) has been synthesized and fully characterized by NMR spectroscopy and single-crystal X-ray diffraction, displaying a separation of 7.433 Å between two Ti centers. The mononuclear complex Me5CpTiMe2-(OC6H3–2,6-iPr2) (Ti1) was also prepared for control experiments. In the presence of [Ph3C][B(C6F5)4] as a cocatalyst, Ti2 shows high activity and thermal stability toward ethylene homopolymerization, similar to those of Ti1. For ethylene/1-octene copolymerization, Ti2 exhibits an extremely high activity of 112800 kg(polymer)·mol–1(Ti)·h–1 at 120 °C that is almost twice that for ethylene homopolymerization, revealing a dramatically positive effect for copolymerization. For ethylene/norbornene (NBE) copolymerization, it is remarkable that Ti2 shows an activity of 9180 kg(polymer)·mol–1(Ti)·h–1 with [NBE] = 2 M under 4 atm of C2H4 and produces the poly(ethylene-co-NBE) copolymer with an Mw of 168 × 104 g·mol–1 and an NBE incorporation of 30.1 mol %, which are 15.3×, 1.2×, and 2.6× those by Ti1 under otherwise identical conditions. In order to study the possible dinuclear cooperativity, the activations of dinuclear Ti2 by [Ph3C][B(C6F5)4] and B(C6F5)3 have been carried out and studied by density functional theory (DFT) and afford an unusual μ-Me bridging dinuclear monocationic species for both cases, revealing that two Ti centers in Ti2 that can possibly interact together with a (co)monomer or propagation chain could lead to synergetic catalysis.