Dichloro-bis(tricyclohexylphosphine)methyleneruthenium

Abstract

[171368-36-8] [(C6H11)3P]2Ru(CH2)Cl2 (MW 746.86) InChI = 1S/2C18H33P.CH2.2ClH.Ru/c2*1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18;;;;/h2*16-18H,1-15H2;1H2;2*1H;/q;;;;;+2/p-2 InChIKey = JPBPDPAGGRDXNP-UHFFFAOYSA-L (metathesis catalysis, ring-closing metathesis (RCM), olefin cross-metathesis, ruthenium alkylidene complex, presumed active catalyst in many ruthenium-catalyzed metathesis reactions) Alternate Name: Grubbs' catalyst. Solubility: dichloromethane, benzene. Form Supplied in: burgundy microcrystalline solid. Preparative Methods: catalyst 1 is most commonly generated in situ upon the first turnover of the more stable and more easily handled catalysts, 2 or 3, in their reaction with terminal alkene substrates. However, a number of general methods have been used to synthesize 1, two in particular have been used most frequently. In the first of these two methods, 1 is formed by a double oxidative addition of [RuH2(H2)2(PCy3)2] or [RuH2(N2)2(PCy3)2] directly to dichloromethane1, 2 or to a higher homolog RC(H)Cl2 (R = Ph, CO2Me) in the presence of ethylene.3 For example,1, 2 CH2Cl2 (0.60 mmol) was added via syringe to a suspension of [RuH2(H2)2(PCy3)2] (0.15 mmol) in pentane (7 mL), and the reaction was stirred under argon at room temperature for 3 h or, alternatively, heated to 60 °C for 15 min. A color change occurs during the course of the reaction; the suspension changing from white to brown-red. The solid was recovered by filtration, washed with pentane, and dried in vacuo to give 1 (63–67%). In a variation of this procedure,2 [RuH2(H2)2(PCy3)2] is first converted to [RuH2(N2)2(PCy3)2] by bubbling N2 through the suspension of [RuH2(H2)2(PCy3)2] in pentane for 15 min, upon which dichloromethane is added. The resulting mixture is stirred for 20 min at room temperature to give 1 (70%) as above. In the second method,4, 5 a cooled (−50 °C) solution of [RuCl2 (PPh3)2] (2.47 mmol) in dichloromethane or pentane (3 mL) is treated with phenyldiazomethane (4.94 mmol). The cold bath is removed and, after 5 min of stirring, the solution is concentrated to ∼3 mL. A color change, orange-brown to brown-green, was observed. Pentane (20 mL) was added to precipitate the solid, which was separated from the mother-liquor via cannula. The solid was redissolved in dichloromethane, and reprecipitated with pentane; this procedure repeated until the mother liquor is nearly colorless. The resulting gray-green microcrystalline solid of [(PPh3)2Cl2Ru = CHPh] was dried under vacuum (89%). The complex was then dissolved in dichloromethane, and 2.2 equiv of tricyclohexylphosphine (PCy3) was added. The solution was stirred for 30 min at room temperature, and then filtered and dried in vacuo. The residue was washed repeatedly with acetone or methanol and dried in vacuo to give 2 (89%) as a purple microcrystalline solid. Compound 2 was then converted into 1 by stirring a solution of 2 in dichloromethane under an atmosphere of ethylene (1 atm) for 15 to 30 min at room temperature. The solvent was removed under vacuum, and the residue washed repeatedly with acetone or pentane (5 mL) to give 1 as a burgundy colored microcrystalline solid in quantitative yield. It was reported that phenyldiazomethane is used to form the intermediate alkylidene [(PPh3)2Cl2Ru = CHPh], because the direct reaction of [RuCl2(PPh3)2] with diazomethane gives a complex mixture of products.5 Ruthenium alkylidenes can also be formed by the reaction of [RuHCl(H2)(PCy3)2] with terminal alkynes6 or with propargyl or vinyl chlorides.7 Purification: repeated washings with pentane or acetone; dried under vacuum for several hours. Handling, Storage, and Precautions: air-stable solid; toxic; decomposition of the complex is observed after 12 h in solution (CH2Cl2 or C6H6) at ambient temperature; faster decomposition rates are observed in heated solutions, for example, the thermolytic half-life of 1 in C6D6 solution at 55 °C is 40 min.