Accessible ring opening metathesis and atom transfer radical polymerization catalysts based on dimethyl sulfoxide ruthenium(II) complexes bearing N-heterocyclic carbene ligands

Abstract Dimethyl sulfoxide ruthenium(II) complexes of N -heterocyclic carbenes derived from cycloalkylamines (cycloalkyl = cyclopentyl ( 1a ), cyclohexyl ( 1b ), cycloheptyl ( 1c ), and cyclooctyl ( 1d )) were synthesized: [RuCl 2 (S-dmso) 2 (IPent)] ( 2a ), [RuCl 2 (S-dmso) 2 (IHex)] ( 2b ), [RuCl 2 (S-dmso) 2 (IHept)] ( 2c ), and [RuCl 2 (S-dmso) 2 (IOct)] ( 2d ). The imidazolium salts 1a - 1d were characterized by FTIR, UV–vis, and 1 H and 13 C NMR spectroscopy, while their respective dimethyl sulfoxide ruthenium(II) complexes ( 2a - 2d ) were characterized by elemental analysis, FTIR, UV–vis, 1 H and 13 C NMR, and cyclic voltammetry. The complexes 2a - 2d were evaluated as catalytic precursors for ROMP of norbornene (NBE) and for ATRP of methyl methacrylate (MMA). The polynorbornene (polyNBE) syntheses via ROMP using the complexes 2a - 2d as pre-catalysts were evaluated under reaction conditions of [EDA]/[Ru] = 28 (5 μL), [NBE]/[Ru] = 5000 at 50 °C as a function of time. The polymerization of MMA via ATRP was conducted using the complexes 2a - 2d in the presence of ethyl 2-bromoisobutyrate (EB i B) as the initiator. All tests were using the molar ratio [MMA]/[EB i B]/[Ru] = 1000/2/1 and conducted at 85 °C. The linear correlation of ln([MMA] 0 /[MMA]) and time clearly indicates that the concentration of radicals remains constant during the polymerization and that the ATRP of MMA mediated by 2a - 2d proceeds in a controlled manner.