Oxidation State Of Catalyst Research Articles

Highly Active and Stable CeO2-Promoted CuCl2/Al2O3 Oxychlorination Catalysts Developed by Rational Design Using a Rate Diagram of the Catalytic Cycle

In this study, we have developed a method to predict the steady-state rate and Cu oxidation state during ethylene oxychlorination from a reaction rate diagram of the individual steps involved in the catalytic oxychlorination cycle. The steady state of the redox cycle is represented by a cross point of the reaction rates of the reduction and oxidation steps as a function of the Cu2+ in the rate diagram. Transient kinetics of elementary reactions and steady-state kinetics of the overall catalytic cycle were investigated in an operando study using combined mass and UV–vis-NIR spectrophotometry. The catalytic consequence of the promoters was then evaluated in terms of reduction and oxidation activity as well as number of active sites, site activity, and the catalyst oxidation state at steady state. Results revealed that the neat CuCl2 catalysts operated at low Cu2+ at the steady-state conditions with stoichiometric feed composition, as a result of relatively low oxidation rate of Cu1+. As a consequence of a h...

Catalytic Activity of Titanium Dioxide Nanoparticles As a Non-Platinum Cathode Catalyst for Oxygen Reduction Reaction

Fuel cells offer potentially efficient, silent and low-pollution electrical power generation. Technical and economic problems have however, restricted their widespread development. One of the principal factors hampering the extensive commercialization of fuel cells is their dependence on platinum as electrocatalysts [1]. In recent years, many attempts have been made to reduce the platinum usage by introducing some metal oxide-based electrocatalysts. As a search of new metal oxide-based electrocatalysts, titanium oxide catalysts were studied for their catalytic activity during the oxygen reduction reaction (ORR) and stability in acid media, especially as a support material. It was reported that titanium oxide supported the oxygen reaction in acid [2] and alkaline [3] media. Early studies on titanium oxide catalysts showed that the catalytic activity for the ORR was low [2], however, Kim et al. [4] later showed that it depends on oxidation state, crystalline structure and work function of the titanium oxide catalysts. Moreover, although previous studies showed that the particle size of nanoparticles electrocatalysts can significantly affect their activity for the ORR [5], no work has been done to investigate the effect of particle size on catalytic performance of titanium oxide nanoparticles electrocatalysts. Therefore, due to some ambiguities and lack of knowledge in this research field, titanium oxide is worth being studied as an independent non-platinum electrocatalyst. In this study, titanium dioxide (TiO2) nanoparticle powders with four different average particle size were purchased and characterized by X-ray diffraction analysis (XRD), small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). The SAXS profiles showed that the particle size maximum probability for TiO2 powders with average particle size of 5 nm, 18 nm, 50 nm and 100 nm were 4 nm, 12 nm, 43 nm and 96 nm, respectively. The SEM images of TiO2 nanoparticle powders showed agglomerated particles with spherical structure that this agglomeration increased with decreasing the size of particles. The XRD patterns indicated anatase and rutile phases for TiO2 nanoparticles. The diffraction intensity of crystal planes for both anatase and rutile phases increased with increasing the particle size which can impact the catalytic activity of TiO2 catalysts for the ORR. The catalytic activity of the catalysts for the ORR was evaluated using cyclic voltammograms (CVs) and linear sweep voltammograms (LSVs) in 0.1 M HClO4 acid solution at 25 ºC. The results shed light on the effect of TiO2 particle size for the ORR.

Cu Model Catalyst Dynamics and CO Oxidation Kinetics Studied by Simultaneous in Situ UV–Vis and Mass Spectroscopy

The oxidation state of Cu nanoparticles during CO oxidation in CO + O2 gas mixtures was sensitively monitored via localized surface plasmon resonances. A microreactor, equipped with in situ UV–vis and mass spectrometry, was developed and used for the measurements. Cu nanoparticles of ∼30 nm average diameter were supported on optically transparent, planar quartz wafers. The aim of the study is 2-fold: (i) to demonstrate the performance and usefulness of the setup and (ii) to use the combined strength of model catalysts and in situ measurements to investigate the correlation between the catalyst oxidation state and its reactivity. Metallic Cu is significantly more active than both Cu(I) and Cu(II) oxides. The metallic Cu phase is only maintained under conditions where close to full oxygen conversion is achieved. This implies that kinetic measurements, aimed at determining the apparent activation energy for metallic Cu under realistic steady-state conditions, are difficult or impossible to perform.

Selectivity Control in the Electroreduction of CO2 over Nanostructured Catalysts

The electrocatalytic reduction of CO2to industrial chemicals and fuels is a promising pathway to sustainable electrical energy storage and to an artificial carbon cycle, but is currently hindered by the low energy efficiency and low activity displayed by traditional electrode materials. In order to overcome these challenges, we have explored how catalyst nanostructure and oxidation state can be used to control the activity and selectivity of the reaction. Using the inverse micelle synthesis method, nanoparticles (NPs) with well-defined size and interparticle distance supported on glassy carbon electrodes were prepared and tested as catalysts for CO2 electroreduction. Previously, we have reported the dramatic effect of the size of these NPs size on activity and selectivity for Cu1 and Au2 NPs. Here, we will show that interparticle distance is also a critical parameter for controlling reactivity.3 For largely spaced NPs, we find that selectivity to CO is enhanced, since this reaction intermediate is less likely to readsorb on neighboring NPs after formation. Large NPs which are highly spaced have slightly higher hydrocarbon selectivity than smaller NPs, since there is more chance for the intermediates to readsorb on the same particle. On the contrary, for closely spaced NPs we find that hydrocarbon selectivity is enhanced, since the re-adsorption of reaction intermediates on neighboring NPs can facilitate the multi-step pathway required for hydrocarbon production. These results are also corroborated by theoretical diffusion calculations. This study addresses previously unexplored aspects of how product selectivity can be controlled using mesoscale transport processes during CO2 electroreduction. In addition, it shows that IP distance is a critical design parameter to consider when developing improved NP catalysts for CO2electroreduction. Another critical parameter for selectivity control in nanostructured electrocatalysts is the oxidation state. We will discuss new oxide-derived metal catalysts that can reduce CO2 with lowered overpotential and improved hydrocarbon selectivity. We will also discuss critical insights into the catalyst reaction mechanism which were unraveled using structural and chemical information on the sample during the reaction using operando X-ray absorption fine structure spectroscopy. References 1) R. Reske, H. Mistry, F. Behafarid, B. Roldan Cuenya, P. Strasser, J. Am. Chem. Soc. (2014) 136: 6978-6986. 2) H. Mistry, R. Reske, Z. Zeng, Z. Zhao, J. Greeley, P. Strasser, B. Roldan Cuenya, J. Am. Chem. Soc. (2014) 136: 16473-16476. 3) H. Mistry, F. Behafarid, R. Reske, A. S. Varela, P. Strasser, B. Roldan Cuenya, ACS Catal. (2015), DOI: 10.1021/acscatal.5b02202.

Electrochemically-controlled grafting of hydrophilic brushes from conducting polymer substrates

Electrochemically-mediated ATRP (eATRP) has emerged in recent years as an alternative controlled radical polymerisation technique that utilises low concentrations of copper-based ATRP catalysts, and that can be conducted in the presence of atmospheric oxygen. In this work, we adapt eATRP to perform surface-initiated electrografting directly from a conducting polymer (CP) macroinitiator that also acts as the working electrode to control catalyst oxidation state, and thereby catalyst activity. Aqueous electrografting of hydrophilic poly(2-hydroxyethyl methacrylate) polymer brushes from the CP macroinitiator, in the presence of an ATRP catalyst (CuBr2/TPMA), was confirmed by ATR-FTIR, water contact angle measurements, and XPS. Optimised grafting conditions were determined whereby polymerisation kinetics approached first order characteristics, as expected for grafting via an eATRP mechanism. However, even under these optimised conditions, we determined that competing electrografting mechanisms were likely occurring, with experiments supporting the occurrence of polymerisation in solution, followed by ⿿grafting to⿿ reactions, as previously described for electrografting via surface electroinitiated emulsion polymerisation (SEEP). Additionally, spectroelectrochemical studies suggest that the mechanism of initiation differs from previously reported eATRP systems in that the conducting polymer itself acts as a co-reductant for the catalyst. As expected, the prevalence of uncontrolled grafting, due to competing grafting mechanisms, as well as effects such as chain termination and degrafting, was highly dependent on polymerisation conditions, most notably on the applied potential.

Platinum–rhodium–tin/carbon electrocatalysts for ethanol oxidation in acid media: effect of the precursor addition order and the amount of tin

Carbon-supported Pt x –Rh y –Sn z catalysts (x:y:z = 3:1:4, 6:2:4, 9:3:4) are prepared by Pt, Rh, and Sn precursors reduction in different addition order. The materials are characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques and are evaluated for the electrooxidation of ethanol in acidic media by cyclic voltammetry, chronoamperometry, and anode potentiostatic polarization. The influence of both the order in which the precursors are added and the composition of metals in the catalysts on the electrocatalytic activity and physico-chemical characteristics of Pt x –Rh y –Sn z /C catalysts is evaluated. Oxidized Rh species prevail on the surface of catalysts synthesized by simultaneous co-precipitation, thus demonstrating the influence of synthesis method on the oxidation state of catalysts. Furthermore, high amounts of Sn in composites synthesized by co-precipitation result in very active catalysts at low potentials (bifunctional effect), while medium Sn load is needed for sequentially deposited catalysts when the electronic effect is most important (high potentials), since more exposed Pt and Rh sites are needed on the catalyst surface to alcohol oxidation. The Pt3–Rh1–Sn4/C catalyst prepared by co-precipitation is the most active at potentials lower than 0.55 V (related to bifunctional effect), while the Pt6–Rh2–Sn4/C catalyst, prepared by sequential precipitation (first Rh and, after drying, Pt + Sn), is the most active above 0.55 V.

Evolution of iron nanoparticles by controlling oxidation states for carbon nanotubes growth

One of the keys to understanding the growth mechanism of carbon nanotubes (CNTs) is the influence of the oxidation states of the iron catalyst nanoparticles. We examined the effect of the oxidation states of iron nanoparticles, which could be controlled by varying the electrical conductivity of the silicon substrate, on the growth of CNTs during thermal chemical vapour deposition. Since the thermal conductivities of the silicon substrate is proportional to its electrical conductivities, thereby catalytic iron thin film on the silicon substrate with higher thermal conductivity could be more affected at the same temperature. The p-type silicon substrates with the electrical conductivities of 1.7 × 10−3/Ω cm (substrate U) and 2.8 × 102/Ω cm (substrate H), respectively, were used in this work. The substrate H allowed that the oxidized iron was more reduced to metallic iron and iron particles grew increasingly larger during annealing under NH3/Ar environment at 900 °C. This size increase is due to the tendency of the reduced metallic iron particles to agglomerate on the substrate. By showing that the oxidation states of iron catalyst could be controlled by the electrical conductivities of the silicon substrates, resulting in the evolution of catalytic nanoparticles for CNTs growth, the electrical conductivities of the substrate could be used as a key parameter for understanding CNTs growth mechanism.

Reduction of Cu-Promoted Fe Model Catalysts Studied by In Situ Indirect Nanoplasmonic Sensing and X-ray Photoelectron Spectroscopy

The reduction of Cu-promoted Fe model catalysts was investigated using X-ray photoelectron spectroscopy (XPS) and indirect nanoplasmonic sensing (INPS). The catalysts were prepared by evaporation of 1 nm thick Fe particle films onto quartz wafers, followed by deposition of 0, 0.2, or 0.02 nm of Cu (i.e., 0, 2, or 19 wt %) as a promoter. For the XPS measurements, a reaction cell with in vacuo transfer to the measurement chamber was used. The catalysts were first oxidized at 400 degrees C in Ar/O-2, achieving fully oxidized Fe2O3 and CuO. Subsequently, the samples were heated to temperatures between 100 and 400 degrees C in pure H-2, and the resulting change in oxidation state was measured. Fe2O3 was found to be reduced to Fe3O4 at 225 degrees C and to a mixed state of FeO and metallic Fe at 275 degrees C. The corresponding temperatures for Cu-promoted Fe catalysts were 100 degrees C lower. In the absence of FeOx, Cu was reduced to metallic Cu, via Cu2O, at temperatures between 125 and 175 degrees C. In addition to the XPS measurements, INPS was used to obtain more detailed insight into the reduction process, both in pure H-2 and in wet H-2, containing 0.8 vol % H2O. These in situ experiments show that the presence of H2O increases the reduction temperature by 36 degrees C or more, depending on the amount of Cu promoter used, where the catalyst with the industrially relevant 2 wt % promoter material exhibits the smallest increase. The INPS measurements also demonstrate that increasing the amount of Cu promoter decreases the Fe2O3 reduction temperature, in both dry and wet H-2. Together, XPS and INPS offer a powerful combination for monitoring the oxidation state of flat model catalysts during pretreatments, an approach that can equally well be used during catalytic reaction conditions.

Combustion synthesis of copper–nickel catalysts for hydrogen production from ethanol

Cu and Ni based catalysts were synthesized using solution combustion synthesis method. The catalytic activity and hydrogen selectivity were investigated for ethanol decomposition reaction. The amount of fuel content in the combustion solution was found to greatly affect the phase and the microstructure of the synthesized catalyst. In situ X-ray absorption spectroscopy (XAS) studies were carried out to study the reduction of the catalyst containing mixed oxides of copper and nickel. The reduced catalyst was further subjected to an oxidizing environment to collect the in situ XAS data during the oxidation of the catalyst. These investigations show that the catalyst oxidation state changes rapidly in the first few minutes of the pretreatment process and then gradually slows downs.

Effect of propene, propane, and methane on conversion and oxidation state of three-way catalysts: a microwave cavity perturbation study

This paper presents laboratory reactor measurements of the steady-state conversion of the pollutants CO, hydrocarbons and NO over a three-way catalyst containing ceria as an oxygen-storage component. It is shown that the presence of the saturated hydrocarbons C3H8 or CH4 causes a shift in the stoichiometry of optimal conversion (CO–NO crossover) to fuel-rich compositions. The shift was more pronounced at lower temperatures and can be explained by the kinetic limitation of the hydrocarbon oxidation reaction. A microwave cavity perturbation technique was used to measure in situ the oxidation state of the ceria. In a first step, titration experiments were performed. The oxygen-storage level was adjusted to a predefined level by equilibration with a H2/H2O mixture. The experiments showed that for a given temperature, the microwave-derived signal (here the resonance frequency) correlates well with the oxidation state of ceria. The microwave cavity perturbation technique was then applied simultaneously to steady-state performance tests in the presence of different hydrocarbons. It was found that if the exhaust stoichiometry is ramped from lean to fuel rich, the CO–NO crossover point in all cases coincides with a strong decrease in the oxidation state of ceria. The correlation between the oxidation state of the catalyst and the catalytic performance is found to be independent of the catalyst temperature and the nature of the hydrocarbon. The CO–NO crossover point can be precisely determined by the microwave cavity perturbation technique. The results suggest that a microwave-based measurement may, under some circumstances, allow for a more precise control of the catalyst performance than the conventional control by lambda sensors.

Electrochemical Study of Cobalt Salen Compounds for Catalytic Biomass Degradation

ABSTRACT Heightened interest in sustainable energy sources have led to a multitude of forays into technologies dealing with biomass refining and energy conversion. While certain streams of biomass offer attractive possibilities as a virtually limitless feedstock, the inherent complexities associated with the constituent biomass polymers, especially the heterogeneous lignin polymer make efficient processing a difficult problem. To make efficient use of lignin as a potential feedstock for energy production or as a chemical precursor, high catalytic specificity and yield is desirable to deal with a broad range of chemical linkages in a manner that results in a single (or few) product(s). In this study, we investigate the use of organometallic Cobalt (salen) complexes and their application toward catalytic breakdown or modification of the lignin polymer. Various lignin model compounds have been used to study possible modes of converting lignin into a usable product in batch reactions with mixed results. In nearly all studies, regardless of yield, the catalyst undergoes deactivation, likely due to an irreversible conformational change or a change in oxidation state of the metal center.By employing non-aqueous cyclic voltammetry, we show that unfixed Co(salen) complexes form a highly reversible redox system. The largely conserved shape of the electrochemical response over successive scans suggests that these catalysts may be recoverable within an electrochemical redox system. Using lignin monomer analogs, we studied electro-catalytic reactions utilizing half-cell cyclic voltammetry and various other characterization techniques to study the electrochemical reversibility of the system and examine the reaction mechanism and oxidation products. Depending on the relative rates of the chemical reaction step and the characteristic response to CV scan rate, the catalytic process defined by the electrochemical oxidation of the catalyst and subsequent chemical reaction step between the ‘activated’ catalyst and the substrate should lead to a “steady state” response similar to that observed for a mass transport limited system. Chemical characterization techniques were also utilized to probe the catalyst oxidation state changes throughout the reaction in an attempt to resolve some of the issues of system deactivation. Keywords : lignin, cobalt salen, electrochemical oxidation, non-aqueous cyclic voltammetry ACKNOWLEDGEMENT We gratefully acknowledge the support of the University of Tennessee Office of the Vice President for Research for support of this work.

Detection of hydrogen peroxide vapor by use of manganese(IV) oxide as catalyst for calorimetric gas sensors

In this work, the catalyst manganese(IV) oxide (MnO2), of calorimetric gas sensors (to monitor the sterilization agent vaporized hydrogen peroxide) has been investigated in more detail. Chemical analyses by means of X‐ray‐induced photoelectron spectroscopy have been performed to unravel the surface chemistry prior and after exposure to hydrogen peroxide vapor at elevated temperature, as applied in the sterilization processes of beverage cartons. The surface characterization reveals a change in oxidation states of the metal oxide catalyst after exposure to hydrogen peroxide. Additionally, a cleaning effect of the catalyst, which itself is attached to the sensor surface by means of a polymer interlayer, could be observed. Schematic demonstrating the principle of the investigated calorimetric hydrogen peroxide gas sensor. Differential set‐up of two temperature‐sensitive elements; right side: passivated by an inert polymer; left side: additionally catalytically activated.

Ethylene Trimerisation with Cr-PNP Catalysts: A Theoretical Benchmarking Study and Assessment of Catalyst Oxidation State

A model for the homogeneous Cr-PNP (PNP = diphosphinoamine) ethylene trimerisation and tetramerisation catalyst system has been studied theoretically, with the aim of identifying suitable density functional theory methods for treatment of this catalyst, and evaluating the likely oxidation and spin states of the active species. Benchmarking studies involving high-level treatment reveal the difficulty of accurately calculating the thermochemistry of this system, and suggest that local density functionals, such as M06L, probably provide the best option. Density functional theory modelling of catalyst activation and the first steps of oligomerisation up until 1-hexene formation appears to favour a CrI–CrIII mechanism, involving spin surface crossing from sextet to quartet states.

ChemInform Abstract: Gold Catalysis: Catalyst Oxidation State Dependent Dichotomy in the Cyclization of Furan—Yne Systems with Aromatic Tethers.

AbstractThis method yields either fluorene derivatives or 2‐furyl‐substituted indene derivatives depending on the applied gold catalyst.

Gold Catalysis: Catalyst Oxidation State Dependent Dichotomy in the Cyclization of Furan–Yne Systems with Aromatic Tethers

Four different synthetic strategies led to a variety of furan-yne systems that contained an aryl system in the tether. Due to the short routes to these systems (four steps or less), a small library of substrates could easily be prepared. These were treated with AuCl(3) or with the Gagosz's catalyst Ph(3)PAuNTf(2) complex. The AuCl(3)-catalyzed reactions delivered highly substituted fluorene derivatives, a class of compounds of great importance as precursors for luminophores with extraordinary abilities. Conversely, a different mechanistic pathway was observed with the cationic gold(I) catalyst. In the latter case, a mechanistically interesting reaction cascade initiated a formal alkyne insertion into the furyl-sp(3)-C bond, which gave indene derivatives as the final products. This new reaction pathway depends on the aromatic moiety in the tether, which stabilizes a crucial cationic intermediate as a benzylic cation.

Role of Catalyst Oxidation State in the Growth of Vertically Aligned Carbon Nanotubes

The impact of gas-phase pretreatment of supported iron-oxide catalyst utilized in aligned carbon nanotube (CNT) growth is studied to understand the correlation between the catalyst oxidation state and the growth characteristics of the aligned CNT forests. By varying the pretreatment conditions from a reducing to an oxidizing environment, notable changes are observed in both the collective CNT array growth behavior and the individual CNT characteristics. Although the greatest catalytic activity was observed following a full reduction to the zerovalent (metallic) Fe catalyst, growth is also observed from a catalyst composed of both Fe2O3 and Fe3O4 particles. XPS core-level analysis, following pretreatment of the catalyst, emphasizes the critical nature of the combined catalyst–underlayer interaction to achieve optimal catalyst activity during growth and hence the most efficient catalyst reduction process. Additionally, CNT diameters during growth were strongly affected by the pretreatment process. Overall, this work gives a collective picture of how the catalyst oxidation state affects the CNT growth based on the catalyst pretreatment environment and the nature of the catalyst–underlayer interactions. Such concepts are critical for the rational design of alternative catalyst–underlayer systems for efficient CNT synthetic processes.

Ceria calcination temperature influence on acetic acid ketonization: Mechanistic insights

The ketonization of carboxylic acids is an attractive method of removing undesirable acidity and oxygen from precursors to biorenewable fuels. However, to be more industrially relevant the ketonization reaction temperature needs to be lowered. Unfortunately, ketonization is not fully understood making this task more challenging. In this work, it was found that the calcination temperature changes the type of interactions that a good ketonization catalyst, cerium oxide, has with the model biomass bio-oil compound acetic acid. Through extensive pre- and post reaction characterization the calcination temperature is determined to influence catalyst final morphology, crystallinity, and oxidation state. Differences in acid, base and redox properties for the ceria calcined at different temperatures did not correlate with the catalytic performance. The crystallinity of the starting ceria, as controlled by the calcinations temperature, was found to dictate whether the reaction proceeds through a bulk or a surface catalyzed mechanism.

Vanadium(III) and vanadium(IV) catalysts in a membrane reactor for benzene hydroxylation to phenol and study of membrane material resistance

Benzene hydroxylation to phenol by using vanadium based catalysts and product recovery were performed in a two-phase membrane reactor. Benzene permeates, through the hydrophobic polypropylene membrane, in the aqueous phase containing the catalyst while phenol permeates back accumulating in the organic phase. The following fundamental aspects have been studied: dose of hydrogen peroxide, initial oxidation states of vanadium catalysts, duration of catalytic tests and lifetime of the membrane in terms of physical and chemical resistance. It was observed that feeding the oxidant by a micro pump, working in the “bulk tube” mode, phenol yield, final phenol concentration in the organic phase, phenol turnover number and system productivity increased, and no tar was formed. Initial oxidation state of vanadium catalysts influenced system performance: indeed improved results in terms of yield (35.2% vs. 25.1%), conversion of hydrogen peroxide to phenol (36.6% vs. 25.9%), productivity (0.97 g gcat−1 h−1 vs. 0.78 g gcat−1 h−1) were obtained by using vanadium(III) chloride compared to vanadium(IV) acetyl acetonate. Higher phenol extraction/recovery in the organic phase (61.1% vs. 46.3%) and then higher selectivity (97.5% vs. 92.8%) were obtained by increasing test duration from 270 to 510min. A weak membrane resistance was observed after 246h of consecutive catalytic runs on the same membrane piece, showing degradation of the membrane material (polypropylene) caused by the OH radical generated in the reacting mixture.

The effect of heat treatment on phase formation of copper manganese oxide: Influence on catalytic activity for ambient temperature carbon monoxide oxidation

The auto-reduction of copper and manganese acetates has been investigated using in situ X-ray diffraction and thermogravimetric analysis, with the intention of manipulating the phenomena to tailor specific phase formation for synthesising catalysts. Subsequently catalysts prepared in this controlled manner were evaluated for ambient temperature CO oxidation. The decomposition of mixed copper and manganese acetate systems was controlled to form MnO x -supported Cu or CuMnO x spinel structures, depending on the oxygen concentration and flow conditions during the heat treatment. Catalyst precursors were prepared by physical grinding and by a supercritical CO 2 anti-solvent precipitation process. The use of supercritical anti-solvent precipitation allows for the formation of well-mixed metal acetates that decompose to form active spinel CO-oxidation catalysts or small copper nano-particles supported on MnO x , depending on the oxygen content of the heat treatment atmosphere. The ability to tune oxidation state and phase composition of catalysts is a key preparation parameter for controlling the activity and provides insight into the active sites for CO oxidation.

N-allyl-N-sulfonyl ynamides as synthetic precursors to amidines and vinylogous amidines. An unexpected N-to-C 1,3-sulfonyl shift in nitrile synthesis.

A detailed study of amidine synthesis from N-allyl-N-sulfonyl ynamides is described here. Mechanistically, this is a fascinating reaction consisting of diverging pathways that could lead to deallylation or allyl transfer depending upon the oxidation state of palladium catalysts, the nucleophilicity of amines, and the nature of the ligands. It essentially constitutes a Pd(0)-catalyzed aza-Claisen rearrangement of N-allyl ynamides, which can also be accomplished thermally. An observation of N-to-C 1,3-sulfonyl shift was made when examining these aza-Claisen rearrangements thermally. This represents a useful approach to nitrile synthesis. While attempts to render this 1,3-sulfonyl shift stereoselective failed, we uncovered another set of tandem sigmatropic rearrangements, leading to vinyl imidate formation. Collectively, this work showcases the rich array of chemistry one can discover using these ynamides.