Olefin Metathesis Reactions Research Articles

Iodonium-Catalyzed Carbonyl–Olefin Metathesis Reactions

The carbonyl–olefin metathesis reaction has become increasingly important in organic synthesis due to its versatility in functional group interconversion chemistry. Recent developments in the field have identified a number of transition-metal and organic Lewis acids as effective catalysts for this reaction. Herein, we report the use of simple organic compounds such as N-iodosuccinimide or iodine monochloride to catalyze the carbonyl–olefin metathesis process under mild reaction conditions. This work broadens the scope of this chemical transformation to include iodonium sources as simple and practical catalysts.

Impact of Unsymmetrical Alkyl–Fluoroalkyl Side Chains over Coil-to-Rod Transition of Soluble Polyacetylenes: Modulation of Electronic Conjugation of Isolated Chains and Their Self-Assembly

Soluble all-trans polyacetylenes (PAs) are most ideal models to study the spectroscopic properties of conjugated polymers for precise control of their backbone configurations, resulting in semiconducting properties for optoelectronic applications. Herein, we report precise control of the backbone configuration and subsequent self-assembly of soluble PAs flanked with alkyl–fluoroalkyl side chains, using light and temperature stimuli respectively in solution. PAs with symmetric alkyl and unsymmetrical alkyl–fluoroalkyl side chains were successfully polymerized by living cyclopolymerization with the olefin metathesis reaction mediated by third-generation Grubbs catalysts. Coil-to-rod-like conformational transition was observed for all of the PAs under ambient light due to photoisomerization, monitored by UV–vis spectroscopy and discussed in terms of the Huang–Rhys parameter. Enrichment of the trans configuration in the conjugated backbones opened up the possibility of aggregation between the isolated conjuga...

Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes Containing Pyrrolide Ligands: Access to Catalysts with Sterically Demanding Alkoxides

All primary data files related to the publication. Procedures, recation conditions and used analytical equipment is discussed in detail in the experimental section or the supporting information of the paper. Productivities in olefin metathesis reactions were examined via gas-chromatography / mass spectrometry (GC-MS) analysis and can be found in the GC-MS folder. Furthermore, the GC-MS folder contains an Excel-file in which the names of the data files are listed and assigned to table entries in the publication. Novel complexes were examined via nuclear magnetic resonance (NMR) spectroscopy and the spectra can be found in NMR folder. The NMR folder also contains NMR experiments mentioned in the paper and shown in the Supplementary Information. NMR Spectra are named according to the numbering in the publication. All crystal data mentioned in the paper can be found in the related datasets.

Concise Seven-Membered Oxepene/Oxepane Synthesis – Structural Motifs in Natural and Synthetic Products

This work outlines a suitable method for the synthesis of oxepane skeleton using iterative C-glycoside technology on the oxepene intermediate, which was synthesized utilizing Wilkinson’s catalyst [Rh(PPh3)3Cl] to generate the isomerized product in a linear synthetic manner. The central core of the oxepene motif was achieved via an olefin metathesis reaction using the Grubbs second-generation and Schrock catalysts. The synthesis of the functionalized oxepane having the desired adriatoxin E-ring relative stereochemistry was achieved starting from commercially available homopropargylic alcohol.

Olefin metathesis of fatty acids and vegetable oils

The article reviews various olefin metathesis reactions namely self-metathesis (SM), cross-metathesis (CM), acyclic diene metathesis (ADMET) polymerization, ring closing metathesis (RCM) and ring opening metathesis (ROM) reactions for the synthesis of a variety of platform chemicals with potential industrial applications from vegetable oils and fatty acids. Different fatty acids employed for various metathesis reactions were oleic, linoleic, linolenic, eicosenoic, erucic, petroselinic, sterculic, undecenoic and ricinoleic acids, while vegetable oils used were Helianthus (sunflower), Brassica napus (rapeseed), Glycine max (soybean), Hevea brasiliensis (rubber), Butea monosperma (palash), Nicotiana tabacum (tobacco) and Sterculia foetida (jangli badam). Even though Grubbs’ catalysts were employed for most of the reactions, other catalysts such as rhenium, molybdenum and tungsten based have also been used for selective reactions of vegetable oils and fatty acids. The article reviews some of the mechanistic pathways involved in the generation of unusual intermediates from fatty acids and triglycerides. Various olefin metathesis reactions namely self-metathesis (SM), crossmetathesis (CM), acyclic diene metathesis (ADMET) polymerization, ring closing metathesis (RCM) and ring opening metathesis (ROM) reactions for the synthesis of a variety of platform chemicals with potential industrial applications from vegetable oils and fatty acids are discussed in this article.

Semiheterogeneous Purification Protocol for the Removal of Ruthenium Impurities from Olefin Metathesis Reaction Products Using an Isocyanide Scavenger

A low-waste, time-economical, and scalable semiheterogeneous purification protocol for the removal of ruthenium residues from olefin metathesis (OM) reactions has been developed. It is based on the non-covalent immobilization of the commercially available isocyanide 1,4-bis(3-isocyanopropyl)piperazine (QA) on unmodified silica gel. The use of the heterogeneous scavenger QA@SiO2 synthesized in situ during the purification process was shown to yield OM products with metal contamination usually below 5 ppm. Furthermore, the new purification protocol was effective on a gram scale in the ring-closing OM of an intermediate in the synthesis of cathepsin K inhibitors, leading to a product containing only 0.29 ppm Ru. Finally, QA was used in an aqueous medium and reduced the metal contamination from 9977 to 21 ppm.

Olefin metathesis in multiblock copolymer synthesis.

Multiblock copolymers constitute a basis for an emerging class of nanomaterials that combine various functional properties with durability and enhanced mechanical characteristics. Our mini-review addresses synthetic approaches to the design of multiblock copolymers from unsaturated monomers and polymers using olefin metathesis reactions and other ways of chemical modification across double C=C bonds. The main techniques, actively developed during the last decade and discussed here, are the coupling of end-functionalized blocks, sequential ring-opening metathesis polymerization, and cross metathesis between unsaturated polymers, or macromolecular cross metathesis. The last topic attracts special interest due to its relative simplicity and broad opportunities to tailor the structure and hence the properties of the copolymer products. Whenever possible, we analyze the structure–property relations for multiblock copolymers and point to their possible practical applications.

Monothiolate ruthenium alkylidene complexes with tricyclic fluorinated N-heterocyclic carbene ligands

New monothiolate ruthenium alkylidene complexes bearing bulky tricyclic N-heterocyclic carbene ligands decorated with two geminal trifluoromethyl groups were synthesized. Their catalytic activity in representative olefin metathesis reactions, such as ring closing metathesis of diallyltosylamine and selfmetathesis of allylbenzene, has been evaluated.

Carbonyl–Olefin Metathesis Catalyzed by Molecular Iodine

The carbonyl–olefin metathesis reaction could facilitate rapid functional group interconversion and allow construction of complicated organic structures. Herein, we demonstrate that elemental iodine, a very simple catalyst, can efficiently promote this chemical transformation under mild reaction conditions. Our mechanistic studies revealed intriguing aspects of the activation mode via molecular iodine and the iodonium ion that could change the previously established perception of catalyst and substrate design for the carbonyl–olefin metathesis reaction.

Synthesizing Stilbene by Olefin Metathesis Reaction Using Guided Inquiry To Compare and Contrast Wittig and Metathesis Methodologies

In this experiment, students are asked to conduct a catalytic cross-metathesis experiment and compare this reaction to the Wittig reaction within the confines of green chemistry. Students synthesize stilbene from styrene using Grubbs second-generation catalyst. Products can be minimally characterized by IR spectroscopy and melting point, but using 1H NMR spectroscopy is preferred. Students find that the Wittig reaction is selective for cis-stilbene while the metathesis reaction produces >98% trans-stilbene. Students determine the cis/trans selectivity, turnover number, and maximum turnover frequency of the reaction. The experiment is conducted alongside the synthesis of stilbene using Wittig chemistry from a published procedure.

Influence of Framework Heteroatoms on Olefin Metathesis Activity Using MoO3-MFI Catalysts

Zeolites with the MFI topology and Si:M (M = Al, B) ranging from pure silica to 20:1 were employed as supports for molybdenum oxide centers to catalyze the olefin metathesis reaction of ethylene and 2-butene to form propylene. Pure-silica MFI doubled the metathesis activity against a comparable amorphous silica support. Incorporation of trivalent aluminum or boron heteroatoms into the MFI support had a significant impact on the catalytic performance. While strongly acidic sites generated by Al incorporation decreased the overall metathesis rate from 1.1 × 10–7 mol s–1 gcat–1 to 3.9 × 10–9 mol s–1 gcat–1 after 8 h on stream, less polarizable sites generated by B incorporation decreased the rate only to 8.3 × 10–8 mol s–1 gcat–1. Na+ and K+ ion exchange of the Al-containing MFI partially mitigated the deleterious effect of the strong Al heteroatoms at the cost of altering the molybdenum configuration away from active states, as observed by Raman spectroscopy. This work demonstrates that structured silica su...

The activity of indenylidene derivatives in olefin metathesis catalysts.

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.

Ruthenium‐Alkylidene Complexes with Sterically Rigid Fluorinated NHC Ligands

An efficient procedure for the preparation of novel olefin metathesis catalysts of Grubbs‐Hoveyda type bearing sterically rigid NHC ligands has been developed. A preliminary evaluation of their catalytic activity has been performed on representative olefin metathesis reactions, such as RCM of malonates as well as self‐metathesis of allylbenzene. As result, it was found that along with excellent robustness, new complexes demonstrate remarkable activity in metathesis of allylbenzene, outperforming commercially available Grubbs‐Hoveyda catalyst in terms of yield and regioselectivity.

Total Synthesis of (±)-Prostratin

Summary Prostratin, a highly complex diterpene natural product, is a pre-clinical candidate in developing a cure for HIV-1 infection and also a potent and selective inhibitor of several tumors. Despite nearly 40 years of progress, prostratin and related natural products still present formidable challenges for synthetic chemists. Here, we report a total synthesis of (±)-prostratin that proceeds in 23 steps from cyclopentadiene. The synthetic strategy includes rapid assembly of the tricyclic core and highly controlled establishment of the densely functionalized C ring, featuring an array of stereoselective transformations including alkoxide-guided 1,4-additions and cyclopropane formation. This work should enable further explorations of chemical and biological spaces based on prostratin and related natural products.

Synthesis of a Helical Analogue of Kekulene: A Flexible π-Expanded Helicene with Large Helical Diameter Acting as a Soft Molecular Spring.

A π-expanded helicene that is the helically twisted analogue of kekulene was synthesized using a 6-fold ring-closing olefin metathesis (RCM) reaction as a key step. The π-expanded geometry with large helical diameter ( dh = 10.2 Å), consisting only of carbon and hydrogen atoms (C54H30), was unambiguously determined by single-crystal X-ray analysis. We found that the π-expanded helicene with large helical diameter will act as a soft molecular spring with a small spring constant. Interestingly, the mechanical properties of the molecular springs roughly satisfied a physical formula for macroscopic spring materials; i.e., the force constant of the elongation of a molecular spring ( k) is inversely proportional to the third power of the helical diameter ( k ∝ dh-3).

SIMes/PCy3mixed ligand-coordinated alkyl group-tagged ruthenium indenylidene complexes: Synthesis, characterization and metathesis activity

We report on the synthesis and characterization of SIMes/PCy3 mixed ligand-coordinated second-generation ruthenium catalysts, bearing various 3-alkyl-1-indenylidene ligands, denoted as RuCl2(3-alkyl-1-indenylidene)(SIMes)(PCy3), in which alkyl is isopropyl (4f), tert-butyl (4g) or cyclohexyl (4h). The characterization of complexes 4f–4h was performed using infrared spectroscopy, elemental analysis, high-resolution mass spectrometry and NMR spectroscopy. In addition, the configuration of complexes 4f and 4g was analyzed using single-crystal X-ray diffraction analysis. The catalytic activities of 4f–4h were evaluated in the olefin metathesis reaction of the ring-closing metathesis of diethyl diallylmalonate, and the ring-opening metathesis polymerization of cis,cis-cyclooctadiene in comparison with the reference complex 4a. The results reveal that all complexes 4a and 4f–4h exhibit similar catalytic activity towards the tested substrates. Careful analysis of the catalyst performance and single-crystal X-ray diffraction data of the obtained complexes reveals that the steric modification on the 3-alkyl group shows a negligible influence on the ligand congestion around the ruthenium center as well as on the catalytic activities in the metathesis reactions.

Effects of Sodium Sulfate and Sodium Chloride for Sonochemical Degradation on 1,4-benzoquinone and Hydroquinone in Aqueous Solution

1,4-benzoquinone, with the molecular formula C6H4O2, is generally known as a para-quinone. It is a six-member ring compound with an oxidized derivative known as 1,4-hydroquinone, which is a bright yellow crystal that has an irritating odour. On the other hand, hydroquinone, also known as benzene-1,4-diol, has the chemical formula C6H4(OH)2. It looks like a white granular solid. Quinone is generally used as a precursor to hydroquinone. The skeletal muscle relaxant, ganglion blocking agent, benzoquinonium, is made from benzoquinone. It is utilized to suppress double-bond migrations during olefin metathesis reactions. 1,4-benzoquinone is also used in the synthesis of Bromodol, while hydroquinone is the main ingredient in black-and-white photographic developers such as film and paper developers, where it diminishes the silver halide to elemental silver. There are various other uses related to this diminishing power. As a polymerization inhibitor, hydroquinone prevents the polymerization of methyl methacrylate, acrylic acid, etc. Studies have demonstrated the various effects of Na2SO4 and NaCl on the sonochemical degradation of 1,4-benzoquinone and hydroquinone using a 200-kHz sonicator. The highest degradation rate was obtained in the presence of 0.433 M Na2SO4 for 1,4-benzoquinone. After 30 minutes of ultrasonic irradiation, the total concentration of 1,4-benzoquinone decreased to 99% in the presence 0.433 M Na2SO4. Without Na2SO4, the sonochemical degradation rate of 1,4-benzoquinone was 4.5 times higher than that of hydroquinone, whereas in the presence of 0.433 M Na2SO4 under the same conditions the initial reaction rate of 1,4-benzoquinone was increased to become 10.6 times higher than that of hydroquinone. On the other hand, in the presence of NaCl, no effects were observed for the decomposition of hydroquinone but negative effects were clearly observed for the decomposition of 1,4-benzoquinone.

Mono- and Bisionic Mo- and W-Based Schrock Catalysts for Biphasic Olefin Metathesis Reactions in Ionic Liquids.

An extensive series of the first ionic Mo- and W-based Schrock-type catalysts based on pyridinium and phosphonium tagged aryloxide ligands were prepared. Bisionic complexes of the general formula Mo(Imido)(CHR)(OR')2 (OTf)2 and monoionic monoaryloxide pyrrolide (pyr) (MAP-type) catalysts [M(Imido)(CHR)(OR')(pyr)+ ][A- ] were successfully employed and tested in various olefin metathesis benchmark reactions under both, homogeneous and biphasic conditions using pyrrole and, for the first time with Schrock-type catalysts, ionic liquids as the polar phase. Productivities under biphasic conditions up to several thousand turn overs were achieved and are comparable to those obtained in reactions carried out in chlorobenzene or toluene. Metal contamination in the nonpolar product-containing heptane phase was <2 ppm.

Ruthenium nanoparticles cofunctionalized with acetylene derivatives of coumarin and perylene: dyad-like intraparticle charge transfer

Nanoparticles are a unique structural scaffold for the fabrication of molecular dyad-like structures, in particular, when the functional moieties are bound onto the nanoparticle surface by conjugated interfacial bonds. In the present study, stable ruthenium nanoparticles (RuHC12) were prepared by the self-assembly of 1-dodecyne onto the nanoparticle surface forming ruthenium–vinylidene interfacial bonds and further functionalized with acetylene derivatives of coumarin and perylene by olefin metathesis reactions. Steady-state photoluminescence measurements of ethynylcoumarin-functionalized ruthenium (RuEC) nanoparticles showed that whereas the excitation and emission maxima remained almost unchanged, the normalized emission intensity was significantly enhanced, as compared to that of RuHC12, due to the much higher quantum yield of the coumarin moieties. By contrast, for the nanoparticles cofunctionalized with ethynylcoumarin and ethynylperylene (RuECEP), the excitation and emission maxima were close to those of ethynylperylene-functionalized ruthenium (RuEP) nanoparticles, but the normalized emissions of RuECEP were markedly quenched as compared to those of RuEP, due to effective photoinduced intraparticle charge transfer from the electron-donating coumarin moieties to the electro-accepting perylene moieties via the conjugated metal–ligand interfacial bonds in RuECEP. This is in sharp contrast to conventional coumarin–perylene dyads where energy transfer plays a dominant role and the perylene emissions were actually markedly enhanced. Consistent results were obtained in time-resolved fluorescence measurements, where RuECEP showed an emission lifetime (6.6 ns) that was longer than that of RuEP (5.0 ns), due to stabilization of the perylene excited state by the electron-donating coumarin groups.

Hoveyda-Grubbs II Catalyst: A Useful Catalyst for One-Pot Visible-Light-Promoted Ring Contraction and Olefin Metathesis Reactions.

A one-pot reaction to synthesize functionalized 2 H-azirines through visible-light-mediated ring contraction and olefin metathesis of isoxazoles is described. Hoveyda-Grubbs II catalyst was found to function as a photocatalyst for these transformations, allowing these processes to be carried out in a one-pot manner. This study offers a new entry for the application of Grubbs catalysts as efficient photocatalysts and the possibilities of carrying out other photoreactions and olefin metathesis in a one-pot process.