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 Ti-2 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 & Aring; between two Ti centers. The mononuclear complex Me5CpTiMe2-(OC6H3-2,6-Pr-i(2)) (Ti-1) was also prepared for control experiments. In the presence of [Ph3C][B(C6F5)(4)] as a cocatalyst, Ti-2 shows high activity and thermal stability toward ethylene homopolymerization, similar to those of Ti-1. For ethylene/1-octene copolymerization, Ti-2 exhibits an extremely high activity of 112800 kg(polymer)<middle dot>mol(-1)(Ti)<middle dot>h(-1) at 120 degrees 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 Ti-2 shows an activity of 9180 kg(polymer)<middle dot>mol(-1)(Ti)<middle dot>h(-1) with [NBE] = 2 M under 4 atm of C2H4 and produces the poly(ethylene-co-NBE) copolymer with an M-w of 168 x 10(4) g<middle dot>mol(-1) and an NBE incorporation of 30.1 mol %, which are 15.3x, 1.2x, and 2.6x those by Ti-1 under otherwise identical conditions. In order to study the possible dinuclear cooperativity, the activations of dinuclear Ti-2 by [Ph3C][B(C6F5)(4)] and B(C6F5)(3) have been carried out and studied by density functional theory (DFT) and afford an unusual mu-Me bridging dinuclear monocationic species for both cases, revealing that two Ti centers in Ti-2 that can possibly interact together with a (co)monomer or propagation chain could lead to synergetic catalysis.