Ruthenium–nickel heterobimetallic complex as a bifunctional catalyst for ROMP of norbornene and ethylene polymerization

Abstract

Monometallic [RuCl₂(η⁶-p-cymene)(pipNH₂)] (mono-Ru) and heterobimetallic [RuCl₂(η⁶-p-cymene)][(μ-Schiff-pip)Ni(PPh₃)Cl] (Ru–Ni) complexes were successfully synthesized. They were fully characterized by FTIR, UV-Vis, and NMR spectroscopic studies, elemental analysis, cyclic voltammetry and computational studies. Complex Ru–Ni was additionally characterized by MALDI-TOF mass spectrometry. The polynorbornene (polyNBE) syntheses via ROMP using mono-Ru and Ru–Ni as pre-catalysts in the presence of ethyl diazoacetate (EDA) were evaluated at different [EDA]/[Ru] ratios, time periods (5–60 min) and temperatures (25 and 50 °C). Higher yields of polyNBE were obtained using [NBE]/[Ru] = 5000 and 5 μL of EDA at 50 °C for 60 min. Under these conditions, mono-Ru exhibited higher catalytic activity than Ru–Ni, reaching 50 and 40% yield, respectively. Hence, a strong steric influence of Ru–Ni on the catalytic activity was demonstrated. The order of magnitude of 10⁵ g mol⁻¹ was measured by SEC for M_n and Đ values ranging from 1.64 to 3.70 for mono-Ru and from 1.26 to 2.40 for Ru–Ni. The catalytic activity of Ru–Ni on ethylene polymerization was evaluated at different [Al]/[Ni] ratios, temperatures (20–60 °C) and reaction times (3–12 h) using MAO as the co-catalyst. Ru–Ni was able to provide an activity of 71.40 kg PE (mol Ni)⁻¹ h⁻¹ at 40 °C after 3 h in a [Al]/[Ni] molar ratio of 2100, 7 μmol of catalyst in 25 mL of toluene and 116 psi ethylene pressure.