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

Abstract

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.