Alkene Groups Research Articles

Stereoselective Palladium-Catalyzed C-F Bond Alkenylation of Tetrasubstituted gem-Difluoroalkenes via Mizoroki-Heck Reaction.

A highly diastereoselective Pd(0)-catalyzed Mizoroki-Heck reaction of gem-difluoroalkenes is described. Unlike previously reported C-F bond functionalization with organometallic reagents, this reaction takes place between two different alkenes to achieve a formal C-F and C-H bond cross-coupling via a distinct pathway. Monofluorinated 1,3-diene products can be synthesized with control of the geometry of each alkene and good functional group tolerability.

EHydrogenation: Hydrogen-free Electrochemical Hydrogenation.

Hydrogenation reactions are staple transformations commonly used across scientific fields to synthesise pharmaceuticals, natural products, and various functional materials. However, the vast majority of these reactions require the use of a toxic and costly catalyst leading to unpractical, hazardous and often functionally limited conditions. Herein, we report a new, general, practical, efficient, mild and high-yielding hydrogen-free electrochemical method for the reduction of alkene, alkyne, nitro and azido groups. Finally, this method has been applied to deuterium labelling.

Mapping and analysis of volatomes from pearl millet (Pennisetum gaucum L.) grains during different storage conditions with solid‐phase microextraction–gas chromatography–mass spectrometry

AbstractBackground and ObjectivesVolatile organic compounds (VOCs) are considered biomarkers for the metabolic activities of biological entities. This work analyzed the impact of storage period and temperature (5°C, 25°C, and 45°C) on the VOC profile of pearl millet grains stored for 120 days through headspace gas analysis using solid‐phase microextraction–gas chromatography–mass spectroscopy (SPME‐GC‐MS).FindingsThe major groups identified in the pearl millet grains belonged to acid, alcohol, aldehyde, alkane, and ester groups. VOC data were analyzed using principal component analysis, partial least square discriminant analysis (PLS‐DA), cluster heat map, and network analysis of metabolite–metabolite interactions. The PLS‐DA could distinctly classify the VOCs generated with respect to different storage conditions. The VOCs generated during storage indicated the four most significant metabolic pathways, that is, fatty acid biosynthesis, cutin, suberine and wax biosynthesis, arginine biosynthesis, and arginine and proline metabolism.ConclusionsThe SPME‐GC‐MS protocol developed for mapping VOC through this study and the classification protocol developed can be used for developing quality monitoring systems in pearl millet grains.Significance and NoveltyIdentification of VOCs at a particular period will be helpful for the recommendation of appropriate remedial measures at the right time to avoid the spoilage of grains.

The "How" and "Where" behind the Functionalization of Graphene Oxide by Thiol-ene "Click" Chemistry.

Graphene oxide (GO) is a 2D nanomaterial with unique chemistry due to the combination of sp2 hybridization and oxygen functional groups (OFGs) even in single layer. OFGs play a fundamental role in the chemical functionalization of GO to produce GO-based materials for diverse applications. However, traditional strategies that employ epoxides, alcohols, and carboxylic acids suffer of low control and undesirable side reactions, including by-product formation and GO reduction. Thiol-ene "click" reaction offers a promising and versatile chemical approach for the alkene functionalization (-C=C-) of GO, providing orthogonality, stereoselectivity, regioselectivity, and high yields while reducing by-products. This review examines the chemical functionalization of GO via thiol-ene "click" reactions, providing insights into the underlying reaction mechanisms, including the role of radical or base catalysts in triggering the reaction. We discuss the "how" and "where" the reaction takes place on GO, the strategies to avoid unwanted side reactions, such as GO reduction and by-product formation. We anticipate that multi-functionalization of GO via the alkene groups will enhance GO physicochemical properties while preserving its intrinsic chemistry.

Pembuatan Sediaan Gel Dari Ekstrak Herba Pegagan (Centella Asiatica L. Urban) Sebagai Obat Luka Sayat

Gotu kola (Centella asiatica L. Urban) contains the active ingredient saponin, an asiaticoside compound that acts as an antibiotic and spurs the production of collagen I, a protein that accelerates the wound healing process. The purpose of this study was to formulate a gel material from ethanol extract of gotu kola herb that meets the requirements of a good gel. In this study, gotu kola saponins were obtained from the extraction process carried out using a stirred extractor at 65°C, 350 rpm and 30, 60, 90, 120, and 150 minutes. Identification of saponins was done using FTIR (Fourier Transform InfraRed). The gel formulation was made with concentrations of 5%, 10%, and 15%. A mass transfer coefficient of 0.01240 min-1 was obtained. The IR spectrum results showed the presence of O-H groups, C-H alkane groups (CH2, CH3), C=O carbonyl groups and C-O ester groups. The results of the evaluation carried out with the three gel concentrations in the organoleptic test, pH test, viscosity test, stability test, adhesion test and spread ability test met the requirements of a good gel.

Roadmap for Postnatal Brain Maturation: Changes in Gray and White Matter Composition during Development Measured by Fourier Transformed Infrared Microspectroscopy.

Key events in postnatal brain development, such as neuronal migration, synaptogenesis, and myelination, shape the adult brain. These events are reflected in changes in gray and white matter (GM and WM) occurring during this period. Therefore, precise knowledge of GM and WM composition in perinatal brain development is crucial to characterizing brain formation as well as the neurodevelopmental disruption observed in diseases such as autism and schizophrenia. In this study, we combined histochemical and immunohistochemical staining with biochemical and biophysical analyses using Fourier transform infrared (IR) microspectroscopy (μFTIR) to better understand the chemical changes during postnatal developmental myelination. For this purpose, we analyzed the GM and WM in the mouse brain and cerebellum (strain C57BL/6) from postnatal day 0 (P0) to day P28 and established presumed correlations between staining and IR data. IR spectra allowed the (i) quantification of lipid and protein content through the CH2/amide I ratio, (ii) determination of chemical characteristics of lipids, such as the presence of unsaturated bonds in the carbonate chain or carbonyls from ester groups in the polar head, and (iii) determination of the protein secondary structure (α-helix and intramolecular β-sheets). The results indicate that the increase in the CH2/amide I ratio calculated from the μFTIR data correlates well with lipid histochemical staining. IR data indicated a change in the lipid composition in WM since carbonyl and unsaturated olefinic groups do not increase when lipids accumulate during myelination. Our correlation analysis between IR data and immunohistochemical staining of myelin-associated proteins revealed that myelin oligodendrocyte protein correlated well with lipid accumulation, while myelin basic protein appeared before lipid modifications, which indicated that myelin-associated proteins and lipid deposition were not synchronic. These events were related to a decrease in the intramolecular β/α protein ratio. Our results indicate that lipids and proteins in WM substantially change their composition due to primary myelination, and according to results obtained from staining, these modifications are better described by lipid histochemical staining than by immunohistochemistry against myelin-related proteins. In conclusion, μFTIR can be a useful technique to study WM during perinatal development and provide detailed information about alterations in the chemical composition related to neurodevelopmental diseases.

Transition Metal-catalyzed Regioselective Direct C-H Arylations Using Quinone Diazide as Arylating Agent: A Mini Review

Abstract: Quinone diazides are a class of diazo compounds, having a planar six-membered ring system with diazo, carbonyl and al-kene groups in conjugation. Earlier it was used in optical, electronic, polymer materials etc. In the last few years, various rearrangements reactions and insertion reactions were explored by these diazo compounds via the formation of metallo-carbenoids. Recently, it has been used to incorporate phenol moieties to hydrocarbons or arene/heteroarenes systems via transition metal-catalyzed C-H bond activation. The reactions proceed via C-H bond insertion or migratory insertion of metal-carbenes. In many cases, the site-selectivities were obtained by the guidance of various directing groups (remova-ble or non-removable). At the same time, several asymmetric approaches were also studied to incorporate phenol deriv-atives to arenes/heteroarenes furnishing compounds showing axial chirality with high stereoselectivity. In this review, we will mainly focus on directed regioselective arylation with quinone diazides under transition metal catalysis through C-H bond activation.

FTIR fingerprinting profiling, antioxidant activity, and α-glucosidase inhibitory activity of Orthosiphon stamineus leaf ethanolic extracts

ABSTRACT Orthosiphon stamineus Benth (O. stamineus) leaves are herb plant parts that can act as an antioxidant and α-glucosidase inhibitor. Finding the best O. stamineus extract that serves as an antioxidant and α-glucosidase inhibitory agent is an essential requirement. Additionally, a clustering analysis based on FTIR spectra should be performed using principal component analysis (PCA) and partial least squares (PLS). Based on this study, the 40% ethanolic extract of O. stamineus leaves is a potent extract as an antioxidant and α-glucosidase inhibitory agent. Whereas 20% ethanolic extract of O. stamineus leaves is only applied as an α-glucosidase agent. Furthermore, discrimination analysis of O. stamineus leaf extracts showed that FTIR-based analysis can discriminate nicely each water, 60%, 80%, and 100% ethanolic extracts. This study reported that the obtained model has the determination coefficient of R2X: 0.991, R2Y: 0.964, and Q2Y: 0.946, which showed a good model and a good prediction. However, the classification method did not distinguish clearly between 20% and 40% ethanolic extracts. 20% ethanolic extract of O. stamineus leaves is always paired with 40% ethanolic extract of O. stamineus. Furthermore, several functional groups from O. stamineus leaf extracts contribute toward both biological activities including alkane groups, carbonyl groups, methylene groups, ester groups, and alkyl di-substitutions. Based on this study, quality control of potent extract as an antioxidant and as an α-Glucosidase Inhibitor should be conducted using a specific marker-based analysis.

Synthesis and Characterization of Activated Carbon/Alginate/Nanocellulose-Cu Composites

OPEFB is one source of natural fiber-based composites which have the potential to become activated carbon and nanocellulose. This study aims to synthesize and characterize the activated carbon/alginate/nanocellulose-Cu composite. The characterization used in this study is FTIR and PSA. The synthesis of activated carbon/alginate/nanocellulose-Cu composites began with a process of carbonization and activation with H3PO4 to produce Activated Carbon. Followed by a bleaching process with NaClO2 and a delignification process with Na2SO3 and NaOH to produce Nanocellulose. Alginate using commercial alginate. Furthermore, the three ingredients were mixed until homogeneous and put into a 0.1M CuSO4 solution to produce beads. The results of the characterization of characterization of PSA Nanocellulose obtained a particle size of 41.05 nm and the result of FTIR characterization on the activated carbon/alginate/nanocellulose-Cu composite contained the functional group OH group, triple C bond from stretching alkyne, C=C aromatic group, C-H alkane group, C-O group, the P=O stretching vibration of the P-O-C group and the alcohol OH group expressing the active carbon; there are functional groups of hydroxyl (OH), carboxyl, carbonyl, and C-O-C and –COOH bonds which represent alginate and there are OH functional groups, stretching C-H bonds, C-O stretching, stretching C-C, and β- glucosidic bonds between glucose units which indicate nanocellulose.

Synthesis and Characterization of Activated Carbon/Alginate-Cu Composites

OPEFB is one source of natural fiber-based composites which have the potential to become activated carbon. This study aims to synthesize and characterize the activated carbon/alginate -Cu composite. The characterization used in this study is FTIR. The results of this study The synthesis of activated carbon/alginate -Cu composites began with a process of carbonization and activation with H3PO4 to produce Activated Carbon. Alginate using commercial alginate. Furthermore, the three ingredients were mixed until homogeneous and put into a 0.1M CuSO4 solution to produce beads. The characterization of FTIR characterization on the activated carbon/alginate-Cu composite contained the functional group OH group, triple C bond from stretching alkyne, C=C aromatic group, C-H alkane group, C-O group , the P=O stretching vibration of the P-O-C group and the alcohol OH group expressing the active carbon; there are functional groups of hydroxyl (OH), carboxyl, carbonyl, and C-O-C and –COOH bonds which represent alginate and there are OH functional groups, stretching C-H bonds, C-O stretching, stretching C-C. The KALg Cu13 sample had a peak at a wavelength of 2838.79 Cm-1 Where the four samples show the presence of C≡N groups.

Physicochemical characterization and mass modelling of Roselle (Hibiscus sabdariffa L.) calyx and seeds

Roselle (Hibiscus sabdariffa L.) calyx and seeds are underutilized, whose utilisation can be widened with the design and development of proper post-harvest systems. For this purpose, a detailed study on its engineering properties is necessary. Hence, the main goals of this study were to investigate the physical, biochemical, thermal, and textural properties of Roselle and to select the most precise models for calculating the mass from its physical properties. Roselle calyx has an average weight of 3.106 g, actual density of 1.04 g/cm3 and bulk density of 0.89 g/cm3. Similarly, Roselle seeds has an average weight of 1.427 g, actual density of 1.37 g/cm3 and bulk density of 0.65 g/cm3. Moreover both the calyx and seeds were found to be rich in protein, phenols and minerals. Finally, the FTIR analysis identified the presence of esters, ethers and carboxylic acids in Calyx and alkyne, alkane, hydroxyl and amide groups in the seeds. In addition, the mass was conducted using four different empirical models, and the power model was found to be the most suitable. The present research will considerably broaden our understanding and be instrumental in creating post-harvest machinery that will increase its value and enable its commercial production.

Metabolomic Profiling of Lactobacillus plantarum Isolated from Ocimum gratissimum Rhizosphere

L. plantarum is a known member of the lactic acid bacteria that possesses antimicrobial activities. Organic acids, hydrogen peroxide and bacteriocins have been majorly identified as the contributors to its antimicrobial activity. The present study sought to employ the GC-MS technique to further classify biological compounds that comprise the antimicrobial metabolite produced by L. plantarum through sub-merged fermentation. The bacterium was isolated from the rhizosphere of O. gratissimum and confirmed using molecular typing. Preliminary antibacterial screening of the organism was done with indicator strains isolated from urinary tract and wound surface, after which sub-merged fermentation was employed for the production of secondary metabolites for a 24 h period. The GC-MS technique was employed to identify the volatile bioactive compounds that comprise the secondary metabolite produced. The organism had significant (p<0.05) inhibition of the indicator strains when compared to the ciprofloxacin standard antibiotic. Metabolomics analyses identified Hydroxylamine, O-decyl-, 2,4-Di-tert-butylphenol, and a wide range of organic compounds mainly from the alkane, amine, carboxylic acids and phenol functional groups, as the components of its antibacterial metabolite. GC-MS based metabolomics analyses is a profitable tool for identifying key components of the antibacterial substance produced by L. plantarum as this will give a room for its bio-prospecting potentials as alternative and sustainable source of novel antimicrobial compounds and other beneficial medications used by humans.

ANALYSIS OF ATTRACTANT COMPOUND FROM PHYTOTELMATA AS BREADING SITE Aedes albopictus

Dengue Hemorrhagic Fever (DHF) has still one of the problem diseases in Indonesia. There has increased in dengue cases in several parts of Indonesia since January 2020 and in the midst of the COVID-19. Very little information about natural breeding sites of Aedes especially of the phytotelmata such as Bambusa sp., Neoregelia spectabilis, Musa paradisiaca, and Cocos nucifera. Other than physical factors of plants, it is suspected that there are attractive compounds produced by these plants. The purpose of this study was to determine the chemical compounds that are attractants from plants used as breeding sites for Ae. albopictus. The research method was started by observation of the presence of Neoregelia spectabilis, Musa paradisiaca, Bambusa sp., and Cocos nucifera plants which contained Ae. albopictus on one of the plant body parts found. Then macerated, purified and analyzed for chemical content using GCMS. The results showed that there were differences in the chemical compounds of plants. The dominant chemical compound is tetracosane. Tetracosane is a chemical compound from the Alkane group. The alkana is an important role in plant interactions such as attractants in the oviposition of certain insects or as attractants for insect feeding activities.

Solubilities and Self-Diffusion Coefficients of Light n-Alkanes in NaCl Solutions at the Temperature Range (278.15-308.15) K and Pressure Range (1-300) bar and Thermodynamics Properties of Their Corresponding Hydrates at (150-290) K and (1-7000) bar.

Continuous Fractional Component Monte Carlo (CFCMC) and molecular dynamics (MD) simulations are performed to calculate the solubilities and self-diffusion coefficients of four light n-alkanes (methane, ethane, propane, and n-butane) in aqueous NaCl solutions as well as the thermodynamic properties of their corresponding hydrate crystals. Correction factors k ij to the Lorentz-Berthelot combining rules for alkane groups (CH3) and water are optimized (k ij = 1.04) by fitting excess chemical potentials to experimental data at 1 bar and 298.15 K. Using these values of k ij , we calculate the solubilities of the four alkanes in aqueous NaCl solutions with different molalities (0-6) mol/kg at different temperatures (278.15-308.15) K and pressures (1, 100, 200, 300) bar. The diffusion coefficients of the four alkanes in NaCl solutions (0-6) mol/kg are calculated at different temperatures (278.15-308.15) K and 1 bar and corrected for the finite-size effects. The lattice parameters of the corresponding hydrates with different guest molecules are computed using MD simulations at different temperatures (150-290) K and pressures (5-700) MPa. Isothermal compressibilities at 287.15 K and thermal expansion coefficients at 14.5 MPa for the corresponding hydrates are calculated. We present an extensive collection of thermodynamic data related to gas hydrates that contribute to a fundamental understanding of natural gas hydrate science.

Phenol Removal Using Granular Dead Anaerobic Sludge Permeable Reactive Barrier in a Simulated Groundwater Pilot Plant

This study investigates the performance of granular dead anaerobic sludge (GDAS) bio-sorbent as permeable reactive barrier in removing phenol from a simulated contaminated shallow groundwater. Batch tests have been performed to characterize the equilibrium sorption properties of the GDAS and sandy soil in phenol-containing aqueous solutions. The results of GDAS tests proved that the best values of operating parameters, which achieve the maximum removal efficiency of phenol (=85%), at equilibrium contact time (=3 hr), initial pH of the solution (=5), initial phenol concentration (=50 mg/l), GDAS dosage (=0.5 g/100 ml), and agitation speed (=250 rpm). Fourier transform infrared (FTIR) analysis proved that the carboxylic acid, aromatic, alkane, alcohol, and alkyl halides groups are responsible for the bio-sorption of phenol onto GDAS.A 2D advection-dispersion, solved numerically by computer solutions (COMSOL) Multiphysics 3.5a software which is based on the finite element method, has been used to simulate the equilibrium transport of phenol within groundwater. This model is taking into account the pollutant sorption onto the GDAS and sandy soil which is represented by Langmuir equation. Numerical and experimental results proved that the barrier plays a potential role in the restriction of the contaminant plume migration. Also, the barrier starts to saturate with contaminant as a function of the travel time. A good agreement between the predicted and experimental results was recognized with root mean squared error not exceeded the 0.055.

Tailoring chemoselectivity of Fe/Ni catalyst for hydrogenation of carbonyl compound

Selective hydrogenation of carbonyl moiety in the presence of olefinic group and other reducible functionality is an industrially important transformation. However, the protocol of green chemistry cannot be sacrificed for its formidable challenging transformation. Therefore, iron nickel bimetallic recyclable catalyst (Fe/Ni) was used for base free hydrogenation of carbonyl compound with high activity and chemoselectivity in microwave environment. The microwave irradiation and pre-treatment of bimetallic catalyst (Fe/Ni) divert conversion/selectivity towards CO group as compared to CC or another reducible moiety. This is further confirmed by DFT calculations which shows that the CO site is strongly interacted with the surface compared to the CC site. The pyridine adsorption studies revealed that pre-treated (Fe/Ni) possess more acidic sites as compared to untreated catalyst. Furthermore, the selectivity of bimetallic catalysts towards hydrogenation of carbonyl function group was correlated with Fe content present in the matrix of catalyst.

Frontiers in Copper-promoted C1-functionalization of Tetrahydroisoquinoline Using Cross-dehydrogenative Coupling

Abstract: The site-selective diversification of molecules is a pertinent unresolved issue within the area of organic chemistry. The functionalization of Csp3-H has changed the landscape of synthetic chemistry by enabling effective direct coupling of compounds and reducing chemical waste by avoiding the usage of pre-functionalized compounds. The 1,2,3,4- tetrahydroisoquinoline (THIQ), a molecule with potential bioactivity, has a stereoselective center at the C1 position. However, there is still a fundamental problem with the C1-functionalization of THIQs. To address this, transition metal-catalyzed cross-dehydrogenative coupling (CDC) has evolved into an essential tool because such reactions can be carried out with enantio-, regio-, and stereoselectivity. In particular, copper-promoted CDC reactions have undoubtedly made substantial progress in THIQ chemistry as a selective protocol. The α-Csp3-H bond adjacent to the Natom of THIQs is activated using copper catalysts, followed by dehydrogenative coupling with various alkynyl, alkane, and alkene groups to form the Csp-Csp3, Csp3-Csp3, and Csp3-Csp2 bonds and produce optically active C1-substituted THIQs. The A3 coupling strategies also produce the endo-yne-THIQs with higher selectivity. This critical discussion highlights all recent advancements (between 2010 and 2022) in CDC reactions to THIQs with the substrate scope and plausible mechanistic routes. This study may be extremely useful to scientists and researchers working on copper-promoted CDC.

Manganese(I)-Catalyzed Chemoselective Transfer Hydrogenation of the C=C Bond in Conjugated Ketones at Room Temperature.

Chemoselective transfer hydrogenation of C=C bond in α,β-unsaturated ketones is demonstrated at room temperature employing a manganese(I) catalyst and half an equivalent of ammonia-borane (H3 N-BH3 ). A series of mixed-donor pincer-ligated Mn(II) complexes, (tBu2 PN3 NPyz )MnX2 [κP ,κN ,κN -(N-(di-tert-butylphosphaneyl)-6-(1H-pyrazol-1-yl)pyridin-2-amine)MnX2 ] {X=Cl (Mn2), X=Br (Mn3), X=I (Mn4)} were synthesized and characterized. Amongst the Mn(II) complexes, (Mn2, Mn3, Mn4) and Mn(I) complex, (tBu2 PN3 NPyz )Mn(CO)2 Br (Mn1) screened; the Mn1 acts as an efficient catalyst for the chemoselective C=C bond reduction in α,β-unsaturated ketones. Various synthetically important functionalities like halides, methoxy, trifluoromethyl, benzyloxy, nitro, amine, and unconjugated alkene and alkyne groups, including heteroarenes, were compatible and provided saturated ketones in excellent yields (up to 97 %). A preliminary mechanistic study highlighted the crucial role of metal-ligand (M-L) cooperation through the dearomatization-aromatization process in catalyst Mn1 for the chemoselective C=C bond transfer hydrogenation.

Fingerprinting FTIR-ATR Fraksi Kopi Robusta dan Arabika serta Korelasinya terhadap Aktivitas Antioksidan

Coffee has a positive effect on health due to its high content of antioxidant compounds. The potential antioxidant activity of coffee is strongly influenced by its chemical compound profile. This study aimed to analyze the effect of different solvents on the chemical metabolites profile, antioxidant activity, and to determine the relevant chemical functional groups which positively contribute to the coffee’s antioxidant activity. In this study, methanolic extract of coffee samples from robusta and arabica varieties were fractionated by liquid-liquid fractionation method using four solvents with different polarities. ABTS (2,2'-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) and cupric reducing antioxidant capacity (CUPRAC) assays were applied to measure the antioxidant activity of the coffee fractions. Fourier Transform Infrared- Attenuated Total Reflectance (FTIR-ATR) based chemometric approach was used to identify the compound functional groups as the fingerprinting profile of the coffee fractions. Correlation between the FTIR-ATR fingerprinting with the antioxidant activity of the coffee fractions was studied using multivariate data analysis, i.e. Principal Component Analysis (PCA) and Orthogonal Partial Least Squares (OPLS). From this study, a reliable PCA model to evaluate the effect of different solvents to FTIR-ATR fingerprinting profile was produced. The correlation between FTIR-ATR fingerprinting profile with the antioxidant activity and the characterization of the chemical functional groups relevant to its antioxidant activity can be analyzed by a reliable OPLS model obtained. This study suggests that the highest antioxidant potential in coffee is found in ethyl acetate fraction both in robusta and arabica coffee samples, while the relevant chemical functional groups having positive correlation to antioxidant activity of coffee were phenol, carbonyl, cyclohexane, aromatic, amide, phenyl, amino, and alkene groups.

A Highly Active Nickel Catalyst for the Selective Hydrogenation of Functionalized Nitroarenes

AbstractThe catalytic hydrogenation of nitroarenes using hydrogen gas as reducing agent to form substituted aniline derivates is an important reaction in industry and academic research. Here, we report on the nitroarene hydrogenation capability of a nanostructured nickel catalyst synthesized from a nickel salen complex and a commercially available porous silica support. Our catalyst allows the selective hydrogenation of nitroarenes under mild conditions while tolerating various functional groups and hydrogenation‐sensitive examples such as iodine, nitrile or olefinic groups. The use of the nickel salen complex as metal precursor is crucial for the high activity and selectivity observed.