Synthesis and Reactivity of Homogeneous and Heterogeneous Ruthenium‐Based Metathesis Catalysts Containing Electron‐Withdrawing Ligands

Abstract

The synthesis and heterogenization of new Grubbs-Hoveyda type metathesis catalysts by chlorine exchange is described. Substitution of one or two chlorine ligands with trifluoroacetate and trifluoromethanesulfonate was accomplished by reaction of [RuCl(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (IMesH(2) = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) with the silver salts CF(3)COOAg and CF(3)SO(3)Ag, respectively. The resulting compounds, [Ru(CF(3)SO(3))(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (1), [RuCl(CF(3)SO(3))([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (2), and [Ru(CF(3)CO(2))(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (3) were found to be highly active catalysts for ring-closing metathesis (RCM) at elevated temperature (45 degrees C), exceeding known ruthenium-based catalysts in catalytic activity. Turn-over numbers (TONs) up to 1800 were achieved in RCM. Excellent yields were also achieved in enyne metathesis and ring-opening cross metathesis using norborn-5-ene and 7-oxanorborn-5-ene-derivatives. Even more important, 3 was found to be highly active in RCM at room temperature (20 degrees C), allowing TONs up to 1400. Heterogeneous catalysts were synthesized by immobilizing [RuCl(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] on a perfluoroglutaric acid derivatized polystyrene-divinylbenzene (PS-DVB) support (silver form). The resulting supported catalyst [RuCl(polymer-CH(2)-O- CO-CF(2)-CF(2)-CF(2)-COO)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (5) showed significantly reduced activities in RCM (TONs = 380) compared with the heterogeneous analogue of 3. The immobilized catalyst, [Ru(polymer-CH(2)-O-CO-CF(2)-CF(2)-CF(2)-COO)(CF(3)CO(2))([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (4) was obtained by substitution of both Cl ligands of the parent Grubbs-Hoveyda catalyst by addition of CF(3)COOAg to 5. Compound 4 can be prepared in high loadings (160 mg catalyst g(-1) PS-DVB) and possesses excellent activity in RCM with TONs up to 1100 in stirred-batch RCM experiments. Leaching of ruthenium into the reaction mixture was unprecedentedly low, resulting in a ruthenium content <70 ppb (ng g(-1)) in the final RCM-derived products.

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.…”

Monolithic Disk‐Supported Metathesis Catalysts for Use in Combinatorial Chemistry

“…Further instrumentation is described elsewhere. [51] Gel permeation chromatography (GPC) using UV/RI/LS detection was carried out on a Waters Styragel column (HR4E 7.8 Â 300 mm) equipped with a Styragel guard column (4.6 Â 30 mm). A 717 plus autosampler, a 2414 differential refractometer, a 484 UV detector (all Waters) and a Minidawn light scattering detector (Wyatt Technologies, USA, l ¼ 690 nm) was used for measurements in CHCl 3 .…”

Ruthenium‐Catalyzed Ring‐Closing Metathesis: Recent Advances, Limitations and Opportunities

“…(It may be noted, however, that protonolyis of the tertbutoxide ligands with HCl can be used to reinstall a chloride ligand, providing a "back-door" route to highly active C16). Higher activity is found for acetate [141,143,147] and sulfonate [143] derivatives. Both catalysts C44 and C45 have been employed at reduced catalyst loadings, offering welcome insight into their "true" activity.…”

“…Attempts to remove the organic fraction by distillation can trigger olefin isomerization, as well as other undesirable reactions catalyzed by the ruthenium species present (see Section 3.2). Several ingenious anchoring strategies have been devised in pursuit of metathesis methodologies that could circumvent these problems [143,151,[159][160][161][162][163][164][165][166]. Use of an anionic donor ligand to tether the catalyst [143] obviates limitations associated with anchoring via a labile L-donor ligand, as well as those inherent in anchoring via the alkylidene itself (the latter strategy necessitating a "release-recapture" mechanism) [159].…”