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Nitro-Grela-type complexes containing iodides - robust and selective catalysts for olefin metathesis under challenging conditions.

ABSTRACT: Iodide-containing nitro-Grela-type catalysts have been synthesized and applied to ring closing metathesis (RCM) and cross metathesis (CM) reactions. These new catalysts have exhibited improved efficiency in the transformation of sterically, non-demanding alkenes. Additional steric hindrance in the vicinity of ruthenium related to the presence of iodides ensures enhanced catalyst stability. The benefits are most apparent under challenging conditions, such as very low reaction concentrations, protic solvents or with the occurrence of impurities.

SUBMITTER: Tracz A

PROVIDER: S-EPMC4660961 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Ruthenium indenylidene "1(st) generation" olefin metathesis catalysts containing triisopropyl phosphite.

Project description:The reaction of triisopropyl phosphite with phosphine-based indenylidene pre-catalysts affords "1(st) generation" cis-complexes. These have been used in olefin metathesis reactions. The cis-Ru species exhibit noticeable differences with the trans-Ru parent complexes in terms of structure, thermal stability and reactivity. Experimental data underline the importance of synergistic effects between phosphites and L-type ligands.

| S-EPMC4578444 | biostudies-literature

Nitro and Other Electron Withdrawing Group Activated Ruthenium Catalysts for Olefin Metathesis Reactions.

Project description:Advanced applications of the Nobel Prize winning olefin metathesis reaction require user-friendly and highly universal catalysts. From many successful metathesis catalysts, which belong to the two distinct classes of Schrock and Grubbs-type catalysts, the subclass of chelating-benzylidene ruthenium complexes (so-called Hoveyda-Grubbs catalysts) additionally activated by electron-withdrawing groups (EWGs) provides a highly tunable platform. In the Review, the origin of the EWG-activation concept and selected applications of the resulting catalysts in target-oriented synthesis, medicinal chemistry, as well as in the preparation of fine-chemicals and in materials chemistry is discussed. Based on the examples, some suggestions for end-users regarding minimization of catalyst loading, selectivity control, and general optimization of the olefin metathesis reaction are provided.

| S-EPMC8246989 | biostudies-literature

Thermally Stable, Latent Olefin Metathesis Catalysts.

Project description:Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C, and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 hours. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C, and exhibited a long catalyst lifetime in solution at elevated temperatures.

| S-EPMC3263927 | biostudies-literature

Olefin metathesis catalysts embedded in ?-barrel proteins: creating artificial metalloproteins for olefin metathesis.

Project description:This review summarizes the recent progress of Grubbs-Hoveyda (GH) type olefin metathesis catalysts incorporated into the robust fold of ?-barrel proteins. Anchoring strategies are discussed and challenges and opportunities in this emerging field are shown from simple small-molecule transformations over ring-opening metathesis polymerizations to in vivo olefin metathesis.

| S-EPMC6278764 | biostudies-literature

Improved ruthenium catalysts for Z-selective olefin metathesis.

Project description:Several new C-H-activated ruthenium catalysts for Z-selective olefin metathesis have been synthesized. Both the carboxylate ligand and the aryl group of the N-heterocyclic carbene have been altered and the resulting catalysts evaluated using a range of metathesis reactions. Substitution of bidentate with monodentate X-type ligands led to a severe attenuation of metathesis activity and selectivity, while minor differences were observed between bidentate ligands within the same family (e.g., carboxylates). The use of nitrato-type ligands in place of carboxylates afforded a significant improvement in metathesis activity and selectivity. With these catalysts, turnover numbers approaching 1000 were possible for a variety of cross-metathesis reactions, including the synthesis of industrially relevant products.

| S-EPMC3257350 | biostudies-literature

Chelated ruthenium catalysts for Z-selective olefin metathesis.

Project description:We report the development of ruthenium-based metathesis catalysts with chelating N-heterocyclic carbene (NHC) ligands that catalyze highly Z-selective olefin metathesis. A very simple and convenient procedure for the synthesis of such catalysts has been developed. Intramolecular C-H bond activation of the NHC ligand, promoted by anion ligand substitution, forms the appropriate chelate for stereocontrolled olefin metathesis.

| S-EPMC3121191 | biostudies-literature

Diphenylamido Precursors to Bisalkoxide Molybdenum Olefin Metathesis Catalysts.

Project description:We have found that Mo(NAr)(CHR')(NPh(2))(2) (R' = t-Bu or CMe(2)Ph) and Mo(NAr')(CHCMe(2)Ph)(NPh(2))(2) (Ar = 2,6-i-Pr(2)C(6)H(3); Ar' = 2,6-Me(2)C(6)H(3)) can be prepared through addition of two equivalents of LiNPh(2) to Mo(NR?)(CHR')(OTf)(2)(dme) species (R? = Ar or Ar' dme = 1,2-dimethoxyethane), although yields are low. A high yield route consists of addition of LiNPh(2) to bishexafluro-t-butoxide species. An X-ray structure of Mo(NAr)(CHCMe(2)Ph)(NPh(2))(2) reveals that the two diphenylamido groups are oriented in a manner that allows an 18 electron count to be achieved. The diphenylamido complexes react readily with t-BuOH and (CF(3))(2)MeCOH, but not readily with the sterically demanding biphenol H(2)[Biphen] (Biphen(2-) = 3,3'-Di-t-butyl-5,5',6,6'-tetramethyl-1,1'-Biphenyl-2,2'-diolate). The diphenylamido complexes do react with various 3,3'-disubstituted binaphthols to yield binaphtholate catalysts that can be prepared in situ and employed for a simple asymmetric ring-closing metathesis reaction. In several cases conversions and enantioselectivities were comparable to reactions in which isolated catalysts were employed.

| S-EPMC2585777 | biostudies-literature

Dipyrrolyl precursors to bisalkoxide molybdenum olefin metathesis catalysts.

Project description:Addition of 2 equiv of lithium pyrrolide to Mo(NR)(CHCMe2R')(OTf)2(DME) (OTf = OSO2CF3; R = 2,6-i-Pr2C6H3, 1-adamantyl, or 2,6-Br2-4-MeC6H2; R' = Me or Ph) produces Mo(NR)(CHCMe2R')(NC4H4)2 complexes in good yield. All compounds can be recrystallized readily from toluene or mixtures of pentane and ether and are sensitive to air and moisture. An X-ray structure of a 2,6-diisopropylphenylimido species shows it to be an unsymmetric dimer, {Mo(NAr)(syn-CHCMe2Ph)(eta5-NC4H4)(eta1-NC4H4)}{Mo(NAr)(syn-CHCMe2Ph)(eta1-NC4H4)2}, in which the nitrogen in the eta5-pyrrolyl bound to one Mo behaves as a donor to the other Mo. All complexes are fluxional on the NMR time scale at room temperature, with one symmetric species being observed on the NMR time scale at 50 degrees C in toluene-d8. The dimers react with PMe3 (at Mo) or B(C6F5)3 (at a eta5-NC4H4 nitrogen) to give monomeric products in high yield. They also react rapidly with 2 equiv of monoalcohols (e.g., Me3COH or (CF3)2MeCOH) or 1 equiv of a biphenol or binaphthol to give 2 equiv of pyrrole and bisalkoxide or diolate complexes in approximately 100% yield.

| S-EPMC2528246 | biostudies-literature

Olefin Metathesis Catalysts Generated In Situ from Molybdenum(VI)-Oxo Complexes by Tuning Pendant Ligands.

Project description:Tailored molybdenum(VI)-oxo complexes of the form MoOCl2 (OR)2 (OEt2 ) catalyse olefin metathesis upon reaction with an organosilicon reducing agent at 70 °C, in the presence of olefins. While this reactivity parallels what has recently been observed for the corresponding classical heterogeneous catalysts based on supported metal oxide under similar conditions, the well-defined nature of our starting molecular systems allows us to understand the influence of structural, spectroscopic and electronic characteristics of the catalytic precursor on the initiation and catalytic proficiency of the final species. The catalytic performances of the pre-catalysts are determined by the highly electron withdrawing (σ-donation) character of alkoxide ligands, Ot BuF9 being the best. This activity correlates with both the 95 Mo chemical shift and the reduction potential that follows the same trend: Ot BuF9 >Ot BuF6 >Ot BuF3 .

| S-EPMC9313794 | biostudies-literature

The activity of indenylidene derivatives in olefin metathesis catalysts.

Project description:The first turnover event of an olefin metathesis reaction using a new family of homogenous Ru-based catalysts bearing modified indenylidene ligands has been investigated, using methoxyethylene as a substrate. The study is carried out by means of density functional theory (DFT). The indenylidene ligands are decorated with ortho-methyl and isopropyl groups at both ortho positions of their phenyl ring. DFT results highlight the more sterically demanding indenylidenes have to undergo a more exothermic first phosphine dissociation step. Overall, the study emphasises advantages of increased steric hindrance in promoting the phosphine release, and the relative stability of the corresponding metallacycle over classical ylidene ligands. Mayer bond orders and steric maps provide structural reasons for these effects, whereas NICS aromaticity and conceptual DFT confirm that the electronic parameters do not play a significant role.

| S-EPMC6278753 | biostudies-other

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