Group 4 Post-Metallocenes Supported by [OCH2N,C(σ-aryl)] Auxiliaries Bearing a Seven-Membered Metallacycle : Synthesis, Characterization, and Catalysts for Olefin Polymerization
Research output: Journal Publications and Reviews › RGC 21 - Publication in refereed journal › peer-review
Author(s)
Related Research Unit(s)
Detail(s)
Original language | English |
---|---|
Pages (from-to) | 2963-2971 |
Number of pages | 9 |
Journal / Publication | Organometallics |
Volume | 38 |
Issue number | 15 |
Online published | 1 Aug 2019 |
Publication status | Published - 12 Aug 2019 |
Link(s)
Abstract
A series of pyridine-2-phenolate-6-(σ-aryl) [OCH2N,C] group 4 bis(benzyl) precatalysts, featuring a flexible O,N-donor chelate, have been prepared and characterized by multinuclear NMR spectroscopy. These complexes adopt C1 symmetry, and variable-temperature 1H NMR experiments for a difluoro-substituted σ-aryl Ti(IV) derivative indicate a fluxional process involving inversion of the seven-membered chelate ring accompanied by conformational changes for the benzyl groups (ΔG‡ = 62.6 kJ mol-1). Scrutiny of the molecular structure of a Zr(IV) relative, determined by X-ray crystallography, revealed severely distorted "quasi-meridional" coordination for the [OCH2N,C] ligand and virtually perpendicular orientation of the benzyl moieties. Olefin polymerization studies have been undertaken in conjunction with methylaluminoxane (MAO) and trityl borate. Using dried MAO (250 equiv) as cocatalyst and 7 atm of ethylene pressure, a CF3-substituted Ti(IV) catalyst displays good activity (680 g mmol-1 h-1 at 75 °C; Mw = 3.4 × 102 kg mol-1, Mw/Mn = 2.6), while the difluoro-substituted analogue produces high molecular-weight polymers (Mw = 1.34 × 103 kg mol-1 at 50 °C; Mw/Mn = 2.4). For the latter derivative, a weak C-H···F-C interaction between a CH2(benzyl) proton and the fluorine atom ortho to the Ti-C(σ-aryl) bond is detected by [1H,19F]-HMQC experiments. These results open up the possibility that such stabilizing interactions could potentially occur for the catalytic species to suppress β-H elimination and hence chain termination processes.
Citation Format(s)
Group 4 Post-Metallocenes Supported by [OCH2N,C(σ-aryl)] Auxiliaries Bearing a Seven-Membered Metallacycle: Synthesis, Characterization, and Catalysts for Olefin Polymerization. / Liu, Cham-Chuen; Liu, Qian; Yiu, Shek-Man et al.
In: Organometallics, Vol. 38, No. 15, 12.08.2019, p. 2963-2971.
In: Organometallics, Vol. 38, No. 15, 12.08.2019, p. 2963-2971.
Research output: Journal Publications and Reviews › RGC 21 - Publication in refereed journal › peer-review