Novel Ruthenium-Based Metathesis Catalysts Containing Electron- Withdrawing Ligands:  Synthesis, Immobilization, and Reactivity

Abstract

The syntheses and reactivity of seven different ruthenium-based metathesis catalysts are described. Ru(CF3COO)2(PCy3)(=CH-2-(2-PrO)C6H4) (1), Ru(CF3COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (2), and Ru(CF3COO)2(PCy(3))(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5) (3) were prepared via chlorine exchange by reacting RuCl2(PCy3)2(=CH-2-(2-PrO)C6H4), RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4), and RuCl2(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5), respectively, with silver trifluoroacetate (Cy =cyclohexyl). In analogy, Ru(CF3CF2COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (4) and Ru(CF3CF2CF2COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (5) were prepared from RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) via reaction with CF3CF2COOAg and CF3CF2CF2COOAg, respectively. Ru(C6F5COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (6) and Ru(C6F5O)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (7) were prepared from RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) via reaction with C6F5COOTl and C6F5OTl, respectively. Supported catalysts Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5) (8), Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(PCy3)(=CH-2-(2-PrO)C6H4) (9), and Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (10) were synthesized by reaction of RuCl2(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5), RuCl2(PCy3)(=CH-2-(2-PrO)C6H4), and RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4), respectively, with a perfluoroglutaric acid-derivatized poly(styrene-co-divinylbenzene) (PS-DVB) support (silver form). Halogen exchange in PCy3-containing systems had to be carried out in dichloromethane in order to suppress precipitation of AgCl.PCy3. The reactivity of all new catalysts in ring-closing metathesis (RCM) of hindered electron-rich and -poor substrates, respectively, at elevated temperature (45 degrees C) was compared with that of existing systems. Diethyl diallylmalonate (DEDAM, 11), diethyl allyl(2-methylallyl)malonate (12), N,N-diallyl-p-toluenesulfonamide (13), N-benzyl-N-but-1-en-4-ylbut-2-enecarboxylic amide (14), and N-allyl-N-(1-carboxymethyl)but-3-en-1-yl-p-toluenesulfonamide (15) were used as educts. Supported catalysts were prepared with high loadings (2.4, 22.1, and 160 mg of catalyst/g PS-DVB for 8, 9, and 10, respectively). Catalyst 8 showed higher and catalysts 9 and 10 sowed significantly reduced activities in RCM compared to their homogeneous analogues. Thus, with 8, turnover numbers (TONs) up to 4200 were realized in stirred-batch (carousel) RCM experiments. To elucidate the nature of the bound species, catalysts 8-10 were subjected to 13C- and 31P-MAS NMR spectroscopy. These investigations provided evidence for the proposed structures. Leaching of ruthenium into the reaction mixture was low, resulting in rutheni...

Strategies to Immobilize Well‐Defined Olefin Metathesis Catalysts: Supported Homogeneous Catalysis vs. Surface Organometallic Chemistry

“…[46] Immobilized Grubbs-Hoveyda or Grubbs-Hoveyda-Grela catalysts can also be prepared on monoliths based on PS-DVB polymers (10e-g). [45,[47][48][49] These catalysts display good performances in RCM. Noteworthy, Ru leaching is very low, and product contamination by Ru is extremely low, i.e., < 100 ppb/ g. Additionally, this property makes them suitable to be used in a continuous flow reactor, where high TON can be achieved (up to several thousands), but deactivation remains a problem, and their performances are still somewhat lower than those of their homogeneous analogues.…”

“…[44] In a similar way, using the hydroxymethylfunctionalized Merrifield resins, the immobilized Grubbs II catalyst can be prepared (10b). [45] A Grubbs II catalyst can also be supported on monoliths (10c) or silica (10d). [46] Immobilized Grubbs-Hoveyda or Grubbs-Hoveyda-Grela catalysts can also be prepared on monoliths based on PS-DVB polymers (10e-g).…”

New Indenylidene‐Schiff Base‐Ruthenium Complexes for Cross‐Metathesis and Ring‐Closing Metathesis

“…[10] This catalyst showed excellent stability towards air and moisture and could be recycled several times. Various other efforts have been directed towards the modification of the Grubbs catalysts, such as the introduction of bidentate Schiff base ligands, [11,12] substituted acetic acid groups, [13][14][15][16] different alkoxides, [17,18] halides, [19] pyridines, [18,20,21] phenoxides, [22,23] less electron-donating phosphines, [24] several pyridinecarboxylates [25] and indenylidene ligand substituting benzylidene. [26,27] Recently, our group has reported new robust ruthenium-indenylidene complexes bearing a saturated N-heterocyclic carbene ligand, showing both high activity and increased stability with an excellent application profile.…”

Aqueous Olefin Metathesis

“…It was closely followed in activity by 85 (30 8C, 55 min, 80 %); the pseudohalide catalyst 86 was the least active (30 8C, 210 min, 27 %). [68] Catalyst 85 was less active in the RCM of 11 in micellar solutions (room temperature, 137 min, 27 %), which indicates that the catalyst and reactant occupy unfavorable positions. It was proposed that the active site of catalyst 85 is in the hydrophilic part of the micelle, whereas the lipophilic diene is localized mostly in the core of the micelle (Scheme 24).…”