Trans-1,2-diphenylethylene linked isoindoline-salicylaldiminato nickel(II) halide complexes: Synthesis, structure, dehydrogenation, and catalytic activity toward olefin homopolymerization

Article abstract of DOI:10.1002/ejic.201201331

Tridentate ligands 4-R¹-6-R²-2-{[trans-2-(isoindolin- 2-yl)-1,2-diphenylethylimino]methyl}phenol [R¹ = R² = H, H(L^a); R¹ = R² = tert-butyl, H(L^b); R¹ = Ph, R² = H, H(L^c)] in which a substituted salicylaldimine moiety and an isoindoline are linked by a trans-1,2- diphenylethylene moiety have been prepared. Deprotonation of these tridentate ligands H(L^a)-H(L^c) by NaH at room temperature in tetrahydrofuran (THF), followed by treatment with 1 equiv. of [(PPh ₃)₂NiX₂] (X = Cl, Br, I) at room temperature afforded the desired nickel complexes [(L)NiX] (X = Cl, L = L^a, 1; X = Cl, L = L^b, 2; X = Cl, L = L^c, 3; X = Br, L = L ^b, 4; X = I, L = L^b, 5) in moderate yields. The structures of 2 and 4 were unequivocally confirmed by single-crystal X-ray diffraction in the solid state. The metal atom has a distorted square-planar coordination geometry and is coordinated to the two nitrogen atoms and one oxygen atom from the tridentate ligand and one halide atom. Dehydrogenation of the chelate tridentate ligand (L^b) in the presence of oxygen afforded the corresponding nickel complexes [(L^b*)NiX] (X = Br, 6; X = I, 7). X-ray analysis showed that in these complexes the two bridged benzylic carbon atoms of (L^b)^- were oxidized and a cis-stilbene moiety, which includes a C=C double bond (1.205-1.268 A) was formed. These nickel complexes with such trans-1,2-diphenylethylene bridged tridentate ligands proved to be active catalysts for ethylene oligomerization in the presence of methylaluminoxane (MAO) and produced butene and hexene with catalytic activities of 0.49 × 10⁵-3.25 × 10⁵ g mol^-1 Ni h^-1 at 30 °C, under 20 bar of ethylene, and with an MAO/Ni ratio of 250. They were also active catalysts for the homopolymerization of norbornene and styrene and displayed activities of up to 1.89 × 10⁵ and 7.36 × 10⁵ g mol^-1 Ni h^-1, respectively. Copyright