Cyclic amines homobimetallic ruthenium pre-catalysts bearing bidentate phosphine and their dual catalytic activity for the ring-opening metathesis and atom-radical polymerizations

Abstract

A series of [RuCl(dppb)(μ-Cl)3Ru(dppb)(amine)] complexes, where amine is pyrrolidine (1), piperidine (2) or perhydroazepine (3), were synthesized and characterized by elemental analysis, FTIR, UV–Vis, and 1H, 13C{1H} and 31P{1H} NMR spectroscopy. The electrochemistry properties of the complexes 1–3 were investigated by cyclic voltammetry and exhibited two successive single-electron oxidation processes. The presence of two redox pairs suggests the formation of a dimeric species in which two different fragments, {Ru(amine)(dppb)} and {RuCl(dppb)}, were connected via three μ-chloro bridges. The complexes 1–3 were evaluated as catalytic precursors for ROMP of norbornene (NBE) and norbornadiene (NBD), as well as for ATRP of methyl methacrylate (MMA). The polynorbornene (polyNBE) syntheses via ROMP using the complexes 1–3 as pre-catalysts were assessed under reaction conditions of [EDA]/[Ru] = 28 (5 μL) and [NBE]/[Ru] = 5000 as a function of time at 25 or 50 °C. Polymerization of MMA via ATRP was conducted using the complexes 1–3 in the presence of ethyl 2-bromoisobutyrate (EBiB) as initiator. Differences in the catalytic activities and polymerization controls were observed in the order 3 > 2 > 1 for both reactions. The activities were discussed considering the steric hindrance and electronic characteristics of the amines as ancillary ligands in the metal center using cyclic voltammetry and NMR studies.