Synthesis and Activity of a New Generation of Ruthenium-Based Olefin Metathesis Catalysts Coordinated with 1,3-Dimesityl-4,5-dihydroimidazol-2-ylidene Ligands

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Representative Procedure for the Preparation of 9a−c.A 500-mL flame-dried Schlenk flask equipped with a magnetic stirbar was charged with 1,3-dimesityl-4,5-dihydroimidazolium tetrafluoroborate (4.02 g, 10.2 mmol, 1.4 equiv) and dry THF (100 mL) under a nitrogen atmosphere. To this suspension was added a solution of potassiumtert-butoxide (1.25 g, 10.2 mmol, 1.4 equiv) in dry THF (200 mL) slowly at room temperature. The tetrafluoroborate salt dissolved immediately to give a cloudy yellow solution. The reaction mixture was allowed to stir at room temperature for 1 h, followed by cannula transfer of the reaction mixture to another 1000-mL flame-dried Schlenk flask under argon. To this solution were added dry benzene (400 mL) and RuCl2(CHPh)(PCy3)2(6.00 g, 7.29 mmol, 1.0 equiv). The reaction mixture was heated at 80 °C for 30 min, at which point the reaction was complete as indicated by1H NMR. The volatiles were removed under high vacuum, and the residue was washed with anhydrous methanol (4 × 100 mL) to give9aas a pinkish-brown microcrystalline solid (4.64 g) in 75% yield: 1H NMR (CD2Cl2, 400 MHz) δ 19.16 (s, 1H), 7.37−7.05 (m, 9H), 3.88 (s, 4H), 2.56−0.15 (m, 51H);31P NMR (CD2Cl2, 161.9 MHz) δ 31.41; HRMS (FAB) C45H65Cl2N2PRu [M+] 848.3306, found 848.3286.

The, 1999, M.

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