Synthesis of Imidazolium-Tagged Ruthenium Carbene Complex: Remarkable Activity and Reusability in Regard to Olefin Metathesis in Ionic Liquids

Abstract

We have demonstrated the synthesis of a new ionic liquid supported ruthenium carbene complex 1a,b and its applications to olefin metathesis. These catalysts can be used for ring-closing metathesis in the construction of five-to-eight-membered rings with high activity and good recyclability.

Keywords

ruthenium - catalysis - metathesis - ionic liquids - carbene complexes

References and Notes

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12

Procedure for the Synthesis of Catalyst 1b
To a solution of 9 (184.9 mg, 0.22 mmol) and CuCl (21.6 mg, 0.22 mmol) in CH₂Cl₂ (20 mL) was added 8b (120.3 mg, 0.26 mmol). The reaction mixture was stirred at reflux for 9 h under argon atmosphere. The volatiles were removed under reduce pressure. The residue was purified by column chromatography on SiO₂ (CH₂Cl₂-acetone, 3:1) to afford 1b (137.2 mg, 68%). ^¹H NMR (400 MHz, CD₂Cl₂): δ = 1.14 (d, J = 6.3 Hz, 6 H), 1.66-1.74 (m, 2 H), 1.89-1.94 (m, 2 H), 2.20-2.65 (br, 18 H), 3.72 (s, 3 H), 4.06 (t, J = 5.7 Hz, 2 H), 4.08 (t, J = 6.9 Hz, 2 H), 4.16 (s, 4 H), 5.64 (sept, J = 6.3 Hz, 1 H), 6.56 (dd, J = 1.3, 7.5 Hz, 1 H), 6.87 (dd, J = 7.5, 8.2 Hz, 1 H), 7.06 (br, 4 H), 7.11 (dd, J = 1.3, 8.2 Hz, 1 H), 7.13 (dd, J = 1.9, 1.9 Hz, 1 H), 7.25 (dd, J = 1.3, 1.9 Hz, 1 H), 8.48 (br, 1 H), 16.57 (s, 1 H). ^¹³C NMR (100 MHz, CD₂Cl₂): δ = 19.6, 21.2, 21.7, 25.4, 26.9, 36.6, 49.9, 51.8, 68.8, 81.0, 115.9, 122.7, 123.9, 124.3, 129.6, 136.0, 136.1, 138.5, 139.3, 140.3, 148.3, 148.6, 210.0, 298.3. IR (KBr): ν = 1574 (w), 1470 (m), 1269 (m) cm^-¹. HRMS-FAB: m/z calcd for C₃₉H₅₁ ^³5Cl₂N₄O₂ ^¹0²Ru: 779.2433; found: 779.2454. Anal. Calcd for C₃₉H₅₁Cl₂F₆N₄O₂PRu: C, 50.65; H, 5.56; N, 6.06. Found: C, 50.62; H, 5.58; N, 5.82.

14

Typical Procedure for Metathesis Reaction Promoted by Ionic Liquid Supported Ruthenium Catalyst
To a catalyst solution of 1b (38.1 mg, 0.04 mmol) in [Bmim]PF₆ (1 mL) was added 10 (0.20 mL, 0.82 mmol) in CH₂Cl₂ (9 mL). The reaction mixture was stirred at r.t. until starting material was consumed. After the volatiles were removed under reduce pressure, ionic liquid phase was extracted with Et₂O (several times). The ethereal phase was evaporated to provide 11, and the ionic liquid phase was dried under reduce pressure to use a catalyst solution for the next cycle.