Tandem ROMP/Vinyl-Addition Polymerization of Norbornene Catalyzed by a Ru/Ni Heterobimetallic Complex

The new compound (1S,4S)-N-(4-iodophenyl)bicyclo[2.2.1]hept-5-en-2-carboxamide (NBE–amide-I) was synthesized using 4-iodoaniline and 5-norbornene-2-carboxylic acid. NBE–amide-I was then used in an oxidative addition reaction with [Ni(PPh₃)₄] to obtain the new complex [NiI(NBE–amide)(PPh₃)₂] (Ni–NBE). The complexes [Ni(NBE–amide)(PPh₃)(Schiff–cyclohexane)] (mono-Schiff–Ni) and [{RuCl₂(η⁶-p-cymene)}μ{(Schiff-pip)Ni(aryl–NBE)(PPh₃)}] (Ru–Ni–NBE) were synthesized via a one-pot reaction using Ni–NBE, salicylaldehyde, and 4-(aminomethyl)piperidine or [RuCl₂(η⁶-p-cymene)(piperidine-(4-aminomethyl))] (mono-RuPip), respectively, in dichloromethane for 16 h. The mono-Ni–Schiff and Ru–Ni–NBE complexes were fully characterized using FTIR, UV–Vis, ¹H and ³¹P{¹H} NMR, MALDI–TOF, EPR, and cyclic voltammetry. These complexes were then evaluated as precatalysts for the vinyl-addition polymerization of norbornene (NBE), achieving yields of 91% and 71%, respectively, using methylaluminoxane (MAO) as the cocatalyst (Al/[Ni] = 2000). Ru–Ni–NBE was also shown to be active in the ring-opening metathesis polymerization (ROMP) of NBE, achieving yields of up to 50% in the presence of 10 equivalents of (trimethylsilyl)diazomethane (TMSDM) as the carbene source. The one-pot synthesis of a copolymer based on assisted-tandem catalysis, combining ROMP and vinyl-addition polymerization of NBE using Ru–Ni–NBE, was conducted through the sequential addition of TMSDM and MAO under previously optimized conditions. The copolymer was characterized by ¹H NMR, GPC, Raman scattering, and SEM.