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

Dimethyl sulfoxide ruthenium(11) complexes of N-heterocyclic carbenes derived from cycloalkylamines (cycloallcyl = cyclopentyl (1a), cyclohexyl (1b), cycloheptyl (1c), and cyclooctyl (1d)) were synthesized: [RuCl2(S-dmso)(2)(IPent)] (2a), [RuCl2(S center dot dmso)(2)(IHex)) (2b), (RuCl2(S-dmso)(2)(IHept)) (2c), and [RuCl2(S center dot dmso)(2)(IOct)) (2d). The imidazolium salts 1a-1d were characterized by FTIR, UV-vis, and H-1 and C-13 NMR spectroscopy, while their respective dimethyl sulfoxide ruthenium(II) complexes (2a-2d) were characterized by elemental analysis, FIR, UV-vis, H-1 and C-13 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 polynorbomene (polyNBE) syntheses via ROMP using the complexes 2a-2d as pre-catalysts were evaluated under reaction conditions of [EDA]/[Ru] = 28 (5 mu L), [NBE]/[Ru] = 5000 at 50 degrees 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 (EBiB) as the initiator. All tests were using the molar ratio [MMA]/[EBiB]/[Ru] = 1000/2/1 and conducted at 85 degrees C. The linear correlation of In([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.