Methylene-bridged bimetallic bis(imino)pyridine-cobaltous chlorides as precatalysts for vinyl-terminated polyethylene waxes

Abstract

Four examples of phenol-substituted methylene-bridged bis(imino)pyridines, CH(C₆H₄-4-OH){2′-(4-C₆H₂-2,6-R²₂NCMe)-6′-(2′′,6′′-R¹₂C₆H₃NCMe)C₅H₃N}₂ [R¹ = R² = Me L1, R¹ = R² = Et L2, R¹ = Et, R² = Me L3, R¹ = ⁱPr, R² = Me L4], have been synthesized and fully characterized. Treatment of L1–L4 with two equivalents of cobaltous chloride affords the bimetallic complexes, [(L)Co₂Cl₄] (L = L1Co1, L2Co2, L3Co3, L4Co4), in good yield. The molecular structure of Co1 shows the two metal centers to be separated by a distance of 13.339 Å with each cobalt displaying a distorted trigonal bipyramidal geometry. On activation with either MAO or MMAO, Co1–Co4 exhibited high activities for ethylene polymerization (up to 1.46 × 10⁷ g(PE) mol⁻¹(Co) h⁻¹ at 50 °C) with their relative values influenced by the steric properties of the N-aryl groups: Co1 > Co3 > Co4 > Co2. Highly linear polyethylenes incorporating high degrees of vinyl end-groups are a feature of all the materials produced with the molecular weights of the MAO-promoted systems (M_w range = 2–8 kg mol⁻¹) generally higher than seen with MMAO (M_w range = 1–3 kg mol⁻¹), while the distributions using MMAO are narrower (PDI < 2.0).