New dimethyl sulfoxide ruthenium(ii) complexes bearing aryl-substituted NHC ligands as pre-catalysts for ROMP of norbornene.

Ruthenium(II) complexes of Schiff base derived from cycloalkylamines (cycloalkyl ¼ cyclopentyl (1a), cyclohexyl (1b), cycloheptyl (1c), and cyclooctyl) (1d) were synthesized: [RuCl(CyPen-Salen)(PPh 3) 2 ] (2a), [RuCl(CyHex-Salen)(PPh 3) 2 ] (2b), [RuCl(CyHep-Salen)(PPh 3) 2 ] (2c), and [RuCl(CyOct-Salen)(PPh 3) 2 ] (2d). The Schiff base-Ru II complexes 2a-d were characterized by elemental analysis, FTIR, UV-Vis, 1 H-, 13 C and 31 P NMR, and cyclic voltammetry. The complexes 2a-d were evaluated as catalytic precursors for ROMP of norbornene (NBE) and for ATRP of methyl methacrylate (MMA). The syntheses of polynorbornene (polyNBE) via ROMP with complexes 2a-d as pre-catalysts were evaluated under different reaction conditions ([HCl]/[Ru], [EDA]/[Ru], [NBE]/[Ru], and temperature). The highest yields of polyNBE were obtained with [NBE]/[HCl]/[Ru] ¼ 5000/25/1 M ratio in the presence of 5 mL of EDA for 60 min at 50 C. MMA polymerization via ATRP was conducted using the complexes 2a-d in the presence of ethyla-bromoisobutyrate (EBiB) as initiator. The catalytic tests were evaluated as a function of the reaction time using the initial molar ratio of [MMA]/[EBiB]/[Ru] ¼ 1000/2/1 at 85 C. The linear correlation of ln([MMA] 0 /[MMA]) and time indicates that the concentration of radicals remains constant during the polymerization and that the ATRP of MMA mediated by 2a-d proceeds in a controlled manner. Molecular weights increased linearly with conversion, however, the experimental molecular weights were higher than the theoretical ones.

Atom transfer radical polymerizations (ATRP) of styrene (St) and methyl methacrylate (MMA) mediated by [RuCl 2 (PPh 3) 2 (amine)] complexes, with amine = pyrrolidine (1), piperidine (2), or perhydroazepine (3), were investigated as a function of time, temperature, and concentrations of monomers and 2-bromoisobutyrate as initiator. The plots of ln([M] 0 /[M]) vs. time and molecular weights vs. monomer conversion were linear and the dispersity indexes decreased with increasing monomer conversions. The complexes 1, 2, and 3 were able to mediate the polymerizations with acceptable rate and level of control. Differences in the rate and control of polymerization were observed in the order 3 > 2 > 1 for both monomers. The activities were discussed considering the steric hindrance and electronic characteristics of the amines as ancillary ligands in the metal centres, considering studies by cyclic voltammetry and NMR.

Monometallic [RuCl2(η6-p-cymene)(pipNH2)] (mono-Ru) and heterobimetallic [RuCl2(p-cymene)](μ-Schiff-pip)Ni(PPh3)Cl] (Ru-Ni) complexes were successfully synthesized. They were fully characterized by FTIR, UV-Vis, and NMR spectroscopic studies, elemental analysis, cyclic voltammetry and computational studies. Complex...

The [Ru(PPh3)2Cl-piperidine(4-aminomethyl)] complex (mono-Ru) was synthesized from [Ru(PPh3)3Cl2] and 4-(aminomethyl)piperidine, whereas the [(PPh3)PdCl(Shiff-pip)] complex (mono-Pd) was obtained by reacting [Pd(PPh3)2Cl2] with its respective Schiff base ligand, both at a 1:1 molar ratio. The heterobimetallic [RuCl2(PPh3)2](μ-Schiff)Pd(PPh3)Cl] complex (Ru/Pd) was synthesized via a one-pot, three-component reaction of mono-Ru, [(Pd(PPh3)2Cl2] and salicylaldehyde. All complexes were fully characterized by FTIR, UV-Vis, and NMR spectroscopy, as well as elemental analysis, MALDI-TOF mass spectrometry, cyclic voltammetry, and computational studies. Ru/Pd was able to polymerize norbornene (NBE) by two different mechanisms: ROMP and vinyl polymerization. The Ru fragment was active for ROMP of NBE, reaching yields of 68 and 31% for mono-Ru and Ru/Pd, respectively, when the [NBE]/[Ru] = 3000 molar ratio and 5 μL EDA addition were employed at 50 °C. The poly(norbornene) (polyNBE) obtained presented an order of magnitude of 104 g mol−1 and Ð values between 1.48 and 1.79. For the vinyl polymerization of NBE, the Pd fragment was active using MAO as a cocatalyst, reaching a yield of 47.0% for Ru/Pd and quantitative yields for mono-Pd when [Al]/[Pd] = 2500 and [NBE]/[Pd] = 20,000 molar ratios were employed, both at 60 °C.

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Arene ruthenium(II) complexes bearing the cyclic amines RuCl2(η6‐p‐cymene)(pyrrolidine)] (1), [RuCl2(η6‐p‐cymene)(piperidine)] (2), and [RuCl2(η6‐p‐cymene)(peridroazepine)] (3) were successfully synthesized. Complexes 1–3 were fully characterized by means of Fourier transform infrared, UV–visible, and NMR spectroscopy, elemental analysis, cyclic voltammetry, computational methods, and one of the complexes was further studied by single crystal X‐ray crystallography. These compounds were evaluated as catalytic precursors for ring‐opening metathesis polymerization (ROMP) of norbornene (NBE) and atom‐transfer radical polymerization (ATRP) of methyl methacrylate (MMA). NBE polymerization via ROMP was evaluated using complexes 1–3 as precatalysts in the presence of ethyl diazoacetate (EDA) under different [NBE]/[EDA]/[Ru] ratios, temperatures (25 and 50°C), and reaction times (5–60 min). The highest yields of polyNBE were obtained with [NBE]/[EDA]/[Ru] = 5000/28/1 for 60 min at 50°C. MMA polymerization via ATRP was conducted using 1–3 as catalysts in the presence of ethyl‐α‐bromoisobutyrate (EBiB) as initiator. The catalytic tests were evaluated as a function of the reaction time using the initial molar ratio of [MMA]/[EBiB]/[Ru] = 1000/2/1 at 95°C. The increase in molecular weight as function of time indicates that complexes 1–3 were able to mediate the MMA polymerization with an acceptable rate and some level of control. Differences in the rate of polymerization were observed in the order 3 > 2 > 1 for the ROMP and ATRP.

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