Carbon–Sulfur Bond Formation of Challenging Substrates at Low Temperature by ...DrMAdamSayah
Pd-PEPPSI-IPent catalyst allows for sulfination reactions of challenging substrates to occur at low temperatures. Reactions proceed smoothly at 40°C for a variety of aryl and heteroaryl halides with aryl, alkyl, and silyl sulfides. The catalyst shows unprecedented reactivity, performing couplings not previously achieved, such as with strongly deactivated substrates. Reactions are also found to occur rapidly at room temperature.
The document describes a proposed study to develop a novel class of photoswitchable carboxylic acids whose acidity can be reversibly controlled by light. Dithienylethene compounds will be synthesized that can switch between open and closed states with different light wavelengths. The closed state is expected to be more conjugated, allowing electron donating/withdrawing substituents to influence acidity. Quantum calculations and acidity comparisons will predict acidity changes between states. Target compounds will be synthesized and characterized, with acidity measurements used to validate light-controlled changes. If successful, these photoswitchable acids could enable new applications in catalysis, biochemistry, and more.
OBC epoxidations paper - Queen Mary University LONDON UK - Thomas FollierThomas Follier
This document reports on a study of the catalytic activity of manganese complexes with two similar polyamine ligands (7 and 8) that differ by the presence of a secondary or tertiary nitrogen, in the epoxidation of styrene. Ligand 7 showed the highest activity with MnSO4 and H2O2, while ligand 8 was most effective with Mn(OTf)2, MnCl2, and Mn(ClO4)2 using peracetic acid. Kinetic analysis indicated the structural differences in the ligands lead to differences in the nature of the active species formed. Ligand 7 with MnSO4 produced the epoxide in 78% yield, while ligand 8 with Mn(OT
Adam B. Powell developed a heterogeneous catalyst composed of palladium, bismuth nitrate, and tellurium metal that promotes the aerobic oxidative esterification of aliphatic alcohols with high yields. The addition of bismuth and tellurium additives significantly increased the rate of product formation and overall yield compared to the catalyst without additives. The catalyst was shown to esterify a variety of activated and aliphatic alcohols, expanding the scope of this transformation. Future work includes adapting the catalyst for other oxidative reactions and developing a robust Pd-Bi-Te catalyst for flow applications.
The document discusses unexpected results from treating MgCl2-supported polypropylene catalysts containing organometallic complexes with additional TiCl4. Adding TiCl4 at a level equal to the existing Ti increased catalyst activity by 70-95% and decreased the polymer melt flow rate by 50%, suggesting a two-component catalyst system. The author proposes the TiCl4 treatment replaces the organometallic complex and frees it to take an external role while restoring the original MgCl2/TiCl4 catalyst. This two-component system provides roughly equal contributions to activity from each component but differing effects on polymer properties like extractables. The author also suggests these complexes could be converted to single-site catalysts using reactive
KEY CONCEPTS
9.1 Catabolic pathways yield energy by oxidizing organic
fuels
9.2 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
9.3 After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules
9.4 During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
9.5 Fermentation and anaerobic respiration enable cells to
produce ATP without the use of oxygen
9.6 Glycolysis and the citric acid cycle connect to many other metabolic pathways
Raj K. Das is conducting research on organoactinides and biomass gasification. He has synthesized a 15-membered macrocycle complex containing catechol and catecholborate ligands around an actinide center. The macrocycle forms through reaction of an organothorium precursor with catecholborane. Similar macrocycles can be prepared with lanthanides and group 4 metals. The macrocycles show some catalytic activity in caprolactone polymerization. For biomass gasification, Raj is screening catalysts such as nickel and uranium oxides to influence the temperature and composition of the syngas produced. He is also working on synthesizing functional copolymers for use in fuel cells.
Carbon–Sulfur Bond Formation of Challenging Substrates at Low Temperature by ...DrMAdamSayah
Pd-PEPPSI-IPent catalyst allows for sulfination reactions of challenging substrates to occur at low temperatures. Reactions proceed smoothly at 40°C for a variety of aryl and heteroaryl halides with aryl, alkyl, and silyl sulfides. The catalyst shows unprecedented reactivity, performing couplings not previously achieved, such as with strongly deactivated substrates. Reactions are also found to occur rapidly at room temperature.
The document describes a proposed study to develop a novel class of photoswitchable carboxylic acids whose acidity can be reversibly controlled by light. Dithienylethene compounds will be synthesized that can switch between open and closed states with different light wavelengths. The closed state is expected to be more conjugated, allowing electron donating/withdrawing substituents to influence acidity. Quantum calculations and acidity comparisons will predict acidity changes between states. Target compounds will be synthesized and characterized, with acidity measurements used to validate light-controlled changes. If successful, these photoswitchable acids could enable new applications in catalysis, biochemistry, and more.
OBC epoxidations paper - Queen Mary University LONDON UK - Thomas FollierThomas Follier
This document reports on a study of the catalytic activity of manganese complexes with two similar polyamine ligands (7 and 8) that differ by the presence of a secondary or tertiary nitrogen, in the epoxidation of styrene. Ligand 7 showed the highest activity with MnSO4 and H2O2, while ligand 8 was most effective with Mn(OTf)2, MnCl2, and Mn(ClO4)2 using peracetic acid. Kinetic analysis indicated the structural differences in the ligands lead to differences in the nature of the active species formed. Ligand 7 with MnSO4 produced the epoxide in 78% yield, while ligand 8 with Mn(OT
Adam B. Powell developed a heterogeneous catalyst composed of palladium, bismuth nitrate, and tellurium metal that promotes the aerobic oxidative esterification of aliphatic alcohols with high yields. The addition of bismuth and tellurium additives significantly increased the rate of product formation and overall yield compared to the catalyst without additives. The catalyst was shown to esterify a variety of activated and aliphatic alcohols, expanding the scope of this transformation. Future work includes adapting the catalyst for other oxidative reactions and developing a robust Pd-Bi-Te catalyst for flow applications.
The document discusses unexpected results from treating MgCl2-supported polypropylene catalysts containing organometallic complexes with additional TiCl4. Adding TiCl4 at a level equal to the existing Ti increased catalyst activity by 70-95% and decreased the polymer melt flow rate by 50%, suggesting a two-component catalyst system. The author proposes the TiCl4 treatment replaces the organometallic complex and frees it to take an external role while restoring the original MgCl2/TiCl4 catalyst. This two-component system provides roughly equal contributions to activity from each component but differing effects on polymer properties like extractables. The author also suggests these complexes could be converted to single-site catalysts using reactive
KEY CONCEPTS
9.1 Catabolic pathways yield energy by oxidizing organic
fuels
9.2 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
9.3 After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules
9.4 During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
9.5 Fermentation and anaerobic respiration enable cells to
produce ATP without the use of oxygen
9.6 Glycolysis and the citric acid cycle connect to many other metabolic pathways
Raj K. Das is conducting research on organoactinides and biomass gasification. He has synthesized a 15-membered macrocycle complex containing catechol and catecholborate ligands around an actinide center. The macrocycle forms through reaction of an organothorium precursor with catecholborane. Similar macrocycles can be prepared with lanthanides and group 4 metals. The macrocycles show some catalytic activity in caprolactone polymerization. For biomass gasification, Raj is screening catalysts such as nickel and uranium oxides to influence the temperature and composition of the syngas produced. He is also working on synthesizing functional copolymers for use in fuel cells.
Kinetics and feasibility studies of thiol oxidation using magnetically separa...Pawan Kumar
This work describes kinetic studies of the catalytic oxidation of thiols (RSHs) found in kerosene to disulphides
using a magnetically separable iron oxide coated Mg-Al layered double hydroxide supported tetra-sulphonated
cobalt phthalocyanine (CoPcS/LDH@Fe3O4) catalyst in an alkali-free environment. Using 1-octanethiol as a representative
RSH, we investigated the effects of different experimental parameters on RSH oxidation kinetics, including
catalyst concentration, temperature (30–60 °C), and initial thiol concentration ([RSH]0, 100–300 ppm).
The catalyst concentration was varied so that the [RSH]0/[Co]tot molar ratio ranged from 45 to 180. Based on
the results, we propose a mechanistic rate expression to explain the observed oxidation of RSH in the presence
of the CoPcS/LDH@Fe3O4 catalyst. The proposed rate law resembles double substrate Michaelis-Menten kinetics,
however, for commonly encountered industrial conditions, we were able to simplify it to a linear form. This rate
law for RSH oxidation can be used to design industrial reactors for an alkali-free sweetening process.
This document describes the discovery of the first organocatalytic α,β,γ-trioxygenation of enals. The reaction proceeds through an initial TEMPO-mediated γ-oxygenation, followed by rapid racemization and reversible conjugate addition of water. This sets the stage for a second TEMPO incorporation at the α-position to set all three stereocenters. Using a tryptophan-derived imidazolidinone catalyst in fluorinated aromatic solvents, α,β,γ-trioxyaldehydes were obtained in up to 51% isolated yield and 85:15 er. Substitution at the δ-position was tolerated, but not at the α, β,
Kinetics and feasibility studies of thiol oxidation using magnetically separa...Pawan Kumar
This research article studies the kinetics of catalytic oxidation of thiols to disulfides using a novel magnetically separable catalyst. The catalyst contains cobalt phthalocyanine grafted onto an iron oxide-coated layered double hydroxide supported on magnetic iron oxide nanoparticles. Experiments were conducted to investigate the effects of various parameters on thiol oxidation kinetics, including catalyst concentration, temperature, and initial thiol concentration. Kinetic data was analyzed to propose a rate law that could be used to design industrial reactors for an alkali-free sweetening process.
This document summarizes research on using amine-rich nitrogen-doped carbon nanodots (NCNDs) as a co-reactant platform for electrochemiluminescence (ECL). The NCNDs were found to enhance the ECL signal of ruthenium tris(bipyridine) through their primary and tertiary amino groups acting as co-reactants in the ECL process. Methylated NCNDs, with tertiary amino groups, showed an even higher ECL signal than unmodified NCNDs. Additionally, a covalently linked hybrid of NCNDs and ruthenium tris(bipyridine) exhibited self-enhanced ECL, with the NCND
The document discusses various types of molecular rearrangement reactions. It begins by defining rearrangement reactions as those where the atoms or groups in a molecule reshuffle to form a structural isomer of the original substance. Rearrangements are then classified as intermolecular or intramolecular. Several examples of nucleophilic rearrangements are provided, including carbonium ion rearrangements like the pinacol-pinacolone, Wagner-Meerwein, and benzillic acid rearrangements. Nitrogen deficiency rearrangements like the Schmidt, Curtius, Hoffmann, Beckmann, and Lossen rearrangements are also briefly described. The mechanisms and features of several important rearrangements are discussed in more detail.
This document summarizes a research article about the synthesis of four-membered heterocycles containing phosphorus, antimony, or bismuth. Specifically, it discusses the synthesis of dipictadiazanes and dipnictadiazenium cations, including [ClE(μ-NTer)]2 (where E = Sb, Bi), [XE(μ-NTer)2E]+, and [E2(μ-NR)2]2+. It describes methods to generate these compounds, such as HCl elimination or using a distannadiazane, as well as challenges in isolating the bismuth derivatives. The synthesis of [IBi(μ-NTer)]2
This document summarizes Lionel Graux's research in organometallic chemistry and homogeneous catalysis. His work focuses on synthesizing new ruthenium complexes using secondary phosphine oxides as ligands. He has characterized the complexes and studied their reactivity and catalytic applications. Specifically, he has investigated their use in catalyzing cycloisomerization of arenynes and C-H bond activation reactions. Additionally, he has explored the alpha-addition of 1,3-diketones to ynamides catalyzed by phosphapalladacycles and ruthenium complexes. His other experience includes developing Buchwald-Hartwig coupling methodology and synthesizing iron complexes for olefin polymerization on an industrial scale.
The document discusses rearrangement reactions, specifically Wagner-Meerwein rearrangements. Wagner-Meerwein rearrangements involve the migration of hydrogen atoms or alkyl groups within carbonium ions, resulting in a rearrangement of carbon skeletons without changing the total number of carbons. Examples given include the neopentyl rearrangement and methyl shifts, such as the conversion of p-xylene to m-xylene. These reactions proceed through a carbonium ion intermediate in which a hydrogen or alkyl group migrates to a more stable position.
The citric acid cycle (CAC) is the final common pathway for the oxidation of nutrients. It occurs in the mitochondria of cells. Acetyl-CoA from various sources enters the CAC and is oxidized to CO2, producing reduced cofactors that drive ATP synthesis. The 8-step cycle produces ATP, GTP, and reduced cofactors NADH and FADH2. Key enzymes and cofactors regulate the cycle in response to energy demands and product inhibition. Anaplerotic reactions maintain CAC intermediate levels.
The document discusses various side reactions that can occur during solid phase peptide synthesis (SPPS), including peptide fragmentation, deletion reactions, β-elimination reactions, rearrangements, cyclizations, modifications of amino acid side chains, and oxidations. Specific examples are provided for each category, such as acidolysis of Asp-Pro bonds and N-acetyl-N-alkyl peptides, β-elimination of cysteine and phosphorylated residues, acid- or base-catalyzed acyl shifts, aspartimide and asparagine deamidation, and disulfide scrambling or degradation. Factors affecting the side reactions like acidity, sequence dependence, and excipient impurities are also examined.
This document summarizes various catalytic mechanisms used by enzymes, including acid-base catalysis, covalent catalysis, metal ion catalysis, electrostatic catalysis, proximity and orientation effects, and preferential transition state binding. It provides examples of each mechanism, such as acid-base catalysis lowering the transition state energy of hydrolysis reactions and coenzymes functioning as covalent catalysts. Metal ions are involved in substrate orientation, oxidation-reduction reactions, and stabilizing charges. Enzyme active sites optimize proximity, orientation and transition state binding to greatly increase reaction rates.
1) The document discusses the effect of water content in hydrogen peroxide on the structure of HTPB produced via the radical polymerization of butadiene.
2) The study found that decreasing the water content of hydrogen peroxide increases the effectiveness of the catalyst in the polymerization process. This leads to increased cis-1,4 HTPB structure and decreased vinyl 1,2 structure in the HTPB product.
3) Kinetic studies showed the reaction is first order with respect to monomer concentration. The formation rates of cis, trans, and vinyl structures could be expressed by rate equations, and decreasing water content had different effects on each rate depending on the power index.
This document discusses using a pseudo-homogeneous CSTR simulation to model a fluidized bed reactor producing polyethylene via gas-phase polymerization including the effect of n-hexane co-solubility predictions using the Sanchez-Lacombe equation of state. The simulation considers an ethylene/nitrogen/n-hexane gas phase in equilibrium with an ethylene/polyethylene/n-hexane polymer phase. Results showed polyethylene production increased about 2% with 0.1 bar of n-hexane due to co-solubility effects. Reactor temperature decreased more sharply in condensed mode with each 0.1 bar increase in n-hexane pressure.
Homogeneous catalysis involves metal complexes in the same phase as reactants, usually liquid. It has advantages like high selectivity and mild reaction conditions. Key aspects include the metal's oxidation state and ligands used. Ligands affect catalysis electronically by donating or accepting electrons from the metal. They also impact catalysis sterically based on their size. The catalytic cycle involves the metal complex having vacant sites for substrates to coordinate through steps like oxidative addition and reductive elimination.
This document provides an overview of homogeneous catalysis and biocatalysis. It discusses various homogeneous catalysts including Wilkinson's catalyst, Ziegler-Natta catalysts, and catalysts used in hydrogenation and hydroformylation reactions. It also discusses the use of enzymes in organic synthesis, including hydrolysis reactions and the synthesis of tartaric acids. Finally, it covers immobilized enzymes and various methods for enzyme immobilization.
This document provides an overview of catalysis. It defines catalysis as a process where a substance called a catalyst alters the rate of a chemical reaction but remains unchanged. Catalytic reactions are classified as homogeneous if reactants and catalysts are in the same phase, or heterogeneous if they are in different phases. Common industrial applications of catalysis include the Haber process for ammonia production and the Contact process for sulfuric acid manufacture. Theories for catalytic mechanisms include intermediate compound formation and adsorption of reactants onto catalyst surfaces.
Carbon−Heteroatom Coupling Using Pd-PEPPSI Complexes (1)DrMAdamSayah
This document summarizes recent advances in using Pd-PEPPSI complexes as catalysts for aryl amination and aryl sulfination reactions. Pd-PEPPSI-IPent was found to be an effective catalyst for aryl sulfinations, enabling the reactions to proceed at 40°C. Further modifications to the pyridine and NHC ligands lowered the activation temperature of the precatalyst to as low as 40°C, allowing the aryl sulfinations to be carried out under very mild conditions. The improved steric environment around Pd is believed to facilitate the initial reductive elimination step needed to generate active Pd(0) and enter the catalytic cycle.
Potassium Isopropoxide- For Sulfination It is the Only Base You Need!DrMAdamSayah
This document summarizes research into improving the efficiency of sulfination reactions using palladium-N-heterocyclic carbene (Pd-NHC) catalyst systems. Key findings include:
1) Potassium isopropoxide alone is sufficient to activate Pd-NHC precatalysts for sulfination, with reactions proceeding smoothly at room temperature.
2) Activation involves reduction of the Pd center from PdII to Pd0, achieved through oxidation of isopropoxide to acetone.
3) An optimized Pd-NHC precatalyst (with 2-methylpyridine ligand) allows a wide variety of sulfination reactions, even of
Computer-assisted study on the reaction between pyruvate and ylide in the pat...Omar Alvarardo
n this study the formation of the lactyl–thia-
min diphosphate intermediate (L–ThDP) is addressed using
density functional theory calculations at X3LYP/6-
31??G(d,p) level of theory. The study includes potential
energy surface scans, transition state search, and intrinsic
reaction coordinate calculations. Reactivity is analyzed in
terms of Fukui functions. The results allow to conclude that
the reaction leading to the formation of L–ThDP occurs via
a concerted mechanism, and during the nucleophilic attack
on the pyruvate molecule, the ylide is in its AP form. The
calculated activation barrier for the reaction is 19.2 kcal/
mol, in agreement with the experimental reported value.
Kinetics and feasibility studies of thiol oxidation using magnetically separa...Pawan Kumar
This work describes kinetic studies of the catalytic oxidation of thiols (RSHs) found in kerosene to disulphides
using a magnetically separable iron oxide coated Mg-Al layered double hydroxide supported tetra-sulphonated
cobalt phthalocyanine (CoPcS/LDH@Fe3O4) catalyst in an alkali-free environment. Using 1-octanethiol as a representative
RSH, we investigated the effects of different experimental parameters on RSH oxidation kinetics, including
catalyst concentration, temperature (30–60 °C), and initial thiol concentration ([RSH]0, 100–300 ppm).
The catalyst concentration was varied so that the [RSH]0/[Co]tot molar ratio ranged from 45 to 180. Based on
the results, we propose a mechanistic rate expression to explain the observed oxidation of RSH in the presence
of the CoPcS/LDH@Fe3O4 catalyst. The proposed rate law resembles double substrate Michaelis-Menten kinetics,
however, for commonly encountered industrial conditions, we were able to simplify it to a linear form. This rate
law for RSH oxidation can be used to design industrial reactors for an alkali-free sweetening process.
This document describes the discovery of the first organocatalytic α,β,γ-trioxygenation of enals. The reaction proceeds through an initial TEMPO-mediated γ-oxygenation, followed by rapid racemization and reversible conjugate addition of water. This sets the stage for a second TEMPO incorporation at the α-position to set all three stereocenters. Using a tryptophan-derived imidazolidinone catalyst in fluorinated aromatic solvents, α,β,γ-trioxyaldehydes were obtained in up to 51% isolated yield and 85:15 er. Substitution at the δ-position was tolerated, but not at the α, β,
Kinetics and feasibility studies of thiol oxidation using magnetically separa...Pawan Kumar
This research article studies the kinetics of catalytic oxidation of thiols to disulfides using a novel magnetically separable catalyst. The catalyst contains cobalt phthalocyanine grafted onto an iron oxide-coated layered double hydroxide supported on magnetic iron oxide nanoparticles. Experiments were conducted to investigate the effects of various parameters on thiol oxidation kinetics, including catalyst concentration, temperature, and initial thiol concentration. Kinetic data was analyzed to propose a rate law that could be used to design industrial reactors for an alkali-free sweetening process.
This document summarizes research on using amine-rich nitrogen-doped carbon nanodots (NCNDs) as a co-reactant platform for electrochemiluminescence (ECL). The NCNDs were found to enhance the ECL signal of ruthenium tris(bipyridine) through their primary and tertiary amino groups acting as co-reactants in the ECL process. Methylated NCNDs, with tertiary amino groups, showed an even higher ECL signal than unmodified NCNDs. Additionally, a covalently linked hybrid of NCNDs and ruthenium tris(bipyridine) exhibited self-enhanced ECL, with the NCND
The document discusses various types of molecular rearrangement reactions. It begins by defining rearrangement reactions as those where the atoms or groups in a molecule reshuffle to form a structural isomer of the original substance. Rearrangements are then classified as intermolecular or intramolecular. Several examples of nucleophilic rearrangements are provided, including carbonium ion rearrangements like the pinacol-pinacolone, Wagner-Meerwein, and benzillic acid rearrangements. Nitrogen deficiency rearrangements like the Schmidt, Curtius, Hoffmann, Beckmann, and Lossen rearrangements are also briefly described. The mechanisms and features of several important rearrangements are discussed in more detail.
This document summarizes a research article about the synthesis of four-membered heterocycles containing phosphorus, antimony, or bismuth. Specifically, it discusses the synthesis of dipictadiazanes and dipnictadiazenium cations, including [ClE(μ-NTer)]2 (where E = Sb, Bi), [XE(μ-NTer)2E]+, and [E2(μ-NR)2]2+. It describes methods to generate these compounds, such as HCl elimination or using a distannadiazane, as well as challenges in isolating the bismuth derivatives. The synthesis of [IBi(μ-NTer)]2
This document summarizes Lionel Graux's research in organometallic chemistry and homogeneous catalysis. His work focuses on synthesizing new ruthenium complexes using secondary phosphine oxides as ligands. He has characterized the complexes and studied their reactivity and catalytic applications. Specifically, he has investigated their use in catalyzing cycloisomerization of arenynes and C-H bond activation reactions. Additionally, he has explored the alpha-addition of 1,3-diketones to ynamides catalyzed by phosphapalladacycles and ruthenium complexes. His other experience includes developing Buchwald-Hartwig coupling methodology and synthesizing iron complexes for olefin polymerization on an industrial scale.
The document discusses rearrangement reactions, specifically Wagner-Meerwein rearrangements. Wagner-Meerwein rearrangements involve the migration of hydrogen atoms or alkyl groups within carbonium ions, resulting in a rearrangement of carbon skeletons without changing the total number of carbons. Examples given include the neopentyl rearrangement and methyl shifts, such as the conversion of p-xylene to m-xylene. These reactions proceed through a carbonium ion intermediate in which a hydrogen or alkyl group migrates to a more stable position.
The citric acid cycle (CAC) is the final common pathway for the oxidation of nutrients. It occurs in the mitochondria of cells. Acetyl-CoA from various sources enters the CAC and is oxidized to CO2, producing reduced cofactors that drive ATP synthesis. The 8-step cycle produces ATP, GTP, and reduced cofactors NADH and FADH2. Key enzymes and cofactors regulate the cycle in response to energy demands and product inhibition. Anaplerotic reactions maintain CAC intermediate levels.
The document discusses various side reactions that can occur during solid phase peptide synthesis (SPPS), including peptide fragmentation, deletion reactions, β-elimination reactions, rearrangements, cyclizations, modifications of amino acid side chains, and oxidations. Specific examples are provided for each category, such as acidolysis of Asp-Pro bonds and N-acetyl-N-alkyl peptides, β-elimination of cysteine and phosphorylated residues, acid- or base-catalyzed acyl shifts, aspartimide and asparagine deamidation, and disulfide scrambling or degradation. Factors affecting the side reactions like acidity, sequence dependence, and excipient impurities are also examined.
This document summarizes various catalytic mechanisms used by enzymes, including acid-base catalysis, covalent catalysis, metal ion catalysis, electrostatic catalysis, proximity and orientation effects, and preferential transition state binding. It provides examples of each mechanism, such as acid-base catalysis lowering the transition state energy of hydrolysis reactions and coenzymes functioning as covalent catalysts. Metal ions are involved in substrate orientation, oxidation-reduction reactions, and stabilizing charges. Enzyme active sites optimize proximity, orientation and transition state binding to greatly increase reaction rates.
1) The document discusses the effect of water content in hydrogen peroxide on the structure of HTPB produced via the radical polymerization of butadiene.
2) The study found that decreasing the water content of hydrogen peroxide increases the effectiveness of the catalyst in the polymerization process. This leads to increased cis-1,4 HTPB structure and decreased vinyl 1,2 structure in the HTPB product.
3) Kinetic studies showed the reaction is first order with respect to monomer concentration. The formation rates of cis, trans, and vinyl structures could be expressed by rate equations, and decreasing water content had different effects on each rate depending on the power index.
This document discusses using a pseudo-homogeneous CSTR simulation to model a fluidized bed reactor producing polyethylene via gas-phase polymerization including the effect of n-hexane co-solubility predictions using the Sanchez-Lacombe equation of state. The simulation considers an ethylene/nitrogen/n-hexane gas phase in equilibrium with an ethylene/polyethylene/n-hexane polymer phase. Results showed polyethylene production increased about 2% with 0.1 bar of n-hexane due to co-solubility effects. Reactor temperature decreased more sharply in condensed mode with each 0.1 bar increase in n-hexane pressure.
Homogeneous catalysis involves metal complexes in the same phase as reactants, usually liquid. It has advantages like high selectivity and mild reaction conditions. Key aspects include the metal's oxidation state and ligands used. Ligands affect catalysis electronically by donating or accepting electrons from the metal. They also impact catalysis sterically based on their size. The catalytic cycle involves the metal complex having vacant sites for substrates to coordinate through steps like oxidative addition and reductive elimination.
This document provides an overview of homogeneous catalysis and biocatalysis. It discusses various homogeneous catalysts including Wilkinson's catalyst, Ziegler-Natta catalysts, and catalysts used in hydrogenation and hydroformylation reactions. It also discusses the use of enzymes in organic synthesis, including hydrolysis reactions and the synthesis of tartaric acids. Finally, it covers immobilized enzymes and various methods for enzyme immobilization.
This document provides an overview of catalysis. It defines catalysis as a process where a substance called a catalyst alters the rate of a chemical reaction but remains unchanged. Catalytic reactions are classified as homogeneous if reactants and catalysts are in the same phase, or heterogeneous if they are in different phases. Common industrial applications of catalysis include the Haber process for ammonia production and the Contact process for sulfuric acid manufacture. Theories for catalytic mechanisms include intermediate compound formation and adsorption of reactants onto catalyst surfaces.
Carbon−Heteroatom Coupling Using Pd-PEPPSI Complexes (1)DrMAdamSayah
This document summarizes recent advances in using Pd-PEPPSI complexes as catalysts for aryl amination and aryl sulfination reactions. Pd-PEPPSI-IPent was found to be an effective catalyst for aryl sulfinations, enabling the reactions to proceed at 40°C. Further modifications to the pyridine and NHC ligands lowered the activation temperature of the precatalyst to as low as 40°C, allowing the aryl sulfinations to be carried out under very mild conditions. The improved steric environment around Pd is believed to facilitate the initial reductive elimination step needed to generate active Pd(0) and enter the catalytic cycle.
Potassium Isopropoxide- For Sulfination It is the Only Base You Need!DrMAdamSayah
This document summarizes research into improving the efficiency of sulfination reactions using palladium-N-heterocyclic carbene (Pd-NHC) catalyst systems. Key findings include:
1) Potassium isopropoxide alone is sufficient to activate Pd-NHC precatalysts for sulfination, with reactions proceeding smoothly at room temperature.
2) Activation involves reduction of the Pd center from PdII to Pd0, achieved through oxidation of isopropoxide to acetone.
3) An optimized Pd-NHC precatalyst (with 2-methylpyridine ligand) allows a wide variety of sulfination reactions, even of
Computer-assisted study on the reaction between pyruvate and ylide in the pat...Omar Alvarardo
n this study the formation of the lactyl–thia-
min diphosphate intermediate (L–ThDP) is addressed using
density functional theory calculations at X3LYP/6-
31??G(d,p) level of theory. The study includes potential
energy surface scans, transition state search, and intrinsic
reaction coordinate calculations. Reactivity is analyzed in
terms of Fukui functions. The results allow to conclude that
the reaction leading to the formation of L–ThDP occurs via
a concerted mechanism, and during the nucleophilic attack
on the pyruvate molecule, the ylide is in its AP form. The
calculated activation barrier for the reaction is 19.2 kcal/
mol, in agreement with the experimental reported value.
Formulation and operation of a Nickel based methanation catalystSakib Shahriar
The objective of this experiment was to get a firsthand experience of the preparation of a catalyst for methanation reaction and to evaluate the performance of the catalyst in a fixed bed tubular reactor. In the first part of the experiment a nickel-based catalyst was synthesized. The catalyst will have nickel as the active component and alumina as the support. the catalyst precursor was prepared by co-precipitation from a solution of nitrate salts of nickel and aluminum. The precipitate was filtered out, washed, dried and calcined to obtain the catalyst. In the second part, the catalyst was activated and performance analysis was done alone with loaded in a fixed bed reactor. The percentage conversion of CO to CH4 was 96.38% and the selectivity of CH4 production to CO2 production was 3.348.
This document describes a catalytic method for synthesizing 5-substituted 1H-tetrazoles using various nitriles and sodium azide. Copper powder and copper sulfate are used to generate active copper(I) catalyst in situ via a comproportionation reaction. This copper(I) species catalyzes the [3+2] cycloaddition of the nitriles and sodium azide to form the tetrazoles in good yields. Reaction calorimetry studies showed the reaction is slightly exothermic and can be safely conducted at 123°C with efficient cooling. A range of structurally diverse nitriles reacted smoothly under these conditions, demonstrating the generality of this copper-catalyzed method for
1) An efficient protocol has been developed for the synthesis of biaryls via Pd/Cu catalyzed coupling of phenylhydrazines in water without using any ligands.
2) Both Pd and Cu catalysts were found to be essential for the reaction, with Pd(TFA)2 and Cu(OAc) providing the best results.
3) A range of substituted phenylhydrazines underwent homo- and cross-coupling reactions under the optimized conditions to provide the biaryl products in good to excellent yields.
OXIDATION OF POLYETHYLENE GLYCOL-200 BY POTASSIUM PERIODATE IN ALKALINE MEDIU...Ratnakaram Venkata Nadh
Kinetics of PEG-200 oxidation by potassium periodatewas studied in alkaline medium. First-order dependence of
reaction on periodate was observed. Rate of the reaction was found to be independent of substrate concentration.
An inverse fractional order with respect to alkaliwas shown. Arrhenius parameters were calculated. Rate law was
postulated taking into consideration of experimental results.
This document discusses hydrogen delivery through liquid organic hydrides (LOH) such as cycloalkanes. It covers considerations for this potential technology, including dehydrogenation catalysts, catalyst supports, and reaction kinetics and thermodynamics. Key points include: (1) Cycloalkanes such as cyclohexane and methylcyclohexane can store 6-8% hydrogen by weight and are liquid at ambient conditions, making them suitable for hydrogen transport. (2) Dehydrogenation over metal catalysts such as Pt is an effective way to release hydrogen from the hydrides. (3) Pt-based catalysts generally have the highest activity and selectivity, while bi-metallic catalysts may have even higher activity through synergistic effects
A facile synthesis method produced highly active Pd nanoparticle catalysts for oxygen reduction reaction (ORR) in under 5 minutes. An electrode was dipped in separate solutions of reducing agent and Pd ions to deposit amorphous Pd nanoparticles. Repeatedly dipping the electrode increased catalytic activity, with the highest activity achieved after 12 cycles of 20 seconds each. The Pd nanoparticles produced using sodium hypophosphite as the reducing agent showed superior ORR activity compared to commercial Pt/C catalysts.
The document summarizes a study on using palladium supported on hydrotalcite as a heterogeneous catalyst for the Suzuki cross-coupling reaction. Various palladium salts were tested as catalysts with different bases and temperatures. PdCl2 supported on hydrotalcite with potassium carbonate as the base provided the best results, with conversions comparable to homogeneous catalysts at temperatures above 90°C. The catalyst was characterized and found to have a palladium content of 1% without changing the structure of the hydrotalcite support. It was an effective catalyst for the reaction, with higher temperatures, bromobenzene, and chlorobenzene providing better conversions than other conditions tested.
Paladio soportado sobre hidrotalcita como un catalizador para la reacción de ...52900339
This document summarizes a study on using palladium supported on hydrotalcite as a catalyst for the Suzuki cross-coupling reaction. Three palladium catalysts were prepared using different palladium salts and hydrotalcite as support. The catalysts were tested in the Suzuki reaction of phenylboronic acid and bromobenzene with various bases. Potassium carbonate provided the best results. The PdCl2-hydrotalcite catalyst gave the highest conversion. Increasing the temperature improved conversion. The catalyst also showed activity for chloro- and fluorobenzenes. The reaction was found to be heterogeneous and the catalyst could be reused after reactivation.
This document summarizes a palladium-catalyzed method for fluorinating arylboronic acid derivatives. Key points:
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- The reaction proceeds through a single-electron transfer pathway involving an isolated and characterized Pd(III) intermediate.
- A wide variety of functional groups are tolerated and the aryl fluoride products are obtained in good yields and purity.
- The reaction is operationally simple and scalable to the multigram level, providing a practical method for synthesizing aryl fluorides.
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The document summarizes a study that used a palladium catalyst to synthesize benzofuran through a Sonogashira coupling reaction between 5-iodovanillin and 3-methyl-3-butyne-2-ol. The reaction was carried out using various amounts of palladium acetate, triphenylphosphine, and solvent. NMR spectroscopy showed the product formed, though it was impure likely due to side reactions promoted by the copper co-catalyst. While the reaction showed good atom economy, the yields were relatively low at 7.45% maximum. Further optimization is needed to improve purity and yields.
The document discusses bio-inspired catalysts for hydrogen production. It begins by noting the importance of hydrogen as an energy carrier and limitations of existing platinum-based catalysts. It then discusses how hydrogenase enzymes provide an efficient model but have limitations as well. Recent research has focused on developing bio-inspired catalysts that incorporate features of the hydrogenase active site and outer coordination sphere to improve catalytic efficiency. Some promising systems discussed include macrocyclic cobalt complexes and nickel bis(diphosphine) complexes containing amino acid groups to mimic the outer coordination sphere, which have shown activity under broader conditions than hydrogenases. Evaluation of catalytic performance focuses on turnover frequency and overpotential.
1) PEPPSI-IPr is a highly efficient palladium catalyst developed for carbon-carbon and carbon-heteroatom bond forming reactions.
2) It demonstrates broad utility in coupling reactions like Negishi, Suzuki, Kumada, Heck, and Buchwald-Hartwig, enabling difficult couplings like alkyl-alkyl.
3) PEPPSI-IPr exhibits good stability and reactivity, working well at room temperature and on large scales, with easy handling and storage compared to traditional phosphine ligands.
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Sulfination Using Pd-PEPPSI Complexes- Studies Into Pre-catalyst Activation, Cationic and Solvent Effect, and Role of Butoxide Base.
1. DOI: 10.1002/chem.201203142
Sulfination by Using Pd-PEPPSI Complexes: Studies into Precatalyst
Activation, Cationic and Solvent Effects and the Role of Butoxide Base**
Mahmoud Sayah,[a]
Alan J. Lough,[b]
and Michael G. Organ*[a]
Introduction
The presence of aryl– and alkyl–sulfur motifs in the struc-
ture of natural products, therapeutics and drug candidates
makes the formation of CÀS linkages an important pursuit
in synthetic chemistry.[1]
Unfortunately, many of the meth-
ods that have been developed to introduce sulfur into target
molecules involve rather harsh conditions, which is especial-
ly true for aryl sulfides.[2]
Catalysis offers the promise of
much gentler reaction conditions although late transition
metals, such as Pd, can be poisoned by the relatively soft
sulfur centre. That said, there have been significant develop-
ments in sulfination by using Pd catalysts with phosphane li-
gands.[3]
The sulfination catalytic cycle (Figure 1) has been thor-
oughly investigated by Hartwig and co-workers, who have
postulated a number of off-cycle resting states (e.g., 3, 6).[4]
To add to these challenges, if reduction [H] of the precata-
lyst (1) is slow, additional deleterious side reactions with Pd
can occur, further compromising catalysis. Unlike the situa-
tion with nucleophilic organometallics in cross coupling, or
alkyl amines in amination chemistry, the mechanism by
which PdII
is reduced to Pd0
is less clear with aryl sulfides.
With phosphane ligands, Hartwig proposed that, although
energetically disfavoured, reductive elimination (RE) of
diaryl disulfide from 3 was the most plausible pathway for
Pd0
(2) to be introduced to the catalytic cycle, given rate
studies in their investigation.[4]
The authors were not able to
confirm the existence of the disulfide in their reactions and
attributed this to its consumption given the reductive condi-
tions of the coupling.
Results and Discussion
Recently we reported that N-heterocyclic carbene (NHC)-
based Pd-PEPPSI-IPent (PEPPSI=pyridine-enhanced pre-
Abstract: The activation of PEPPSI
precatalysts has been systematically
studied in Pd-catalysed sulfination.
Under the reactions conditions of the
sulfide and KOtBu in toluene, the first
thing that happens is exchange of the
two chlorides on the PEPPSI precata-
lyst with the corresponding sulfides,
creating the first resting state; it is via
this complex that all Pd enters the cat-
alytic cycle. However, it is also from
this same complex that a tri-Pd com-
plex forms, which is a more persistent
resting state. Under standard reaction
conditions, this complex is catalytically
inactive. However, if additional pyri-
dine or a smaller base (i.e., KOEt) is
added, this complex is broken down,
presumably initially back to the first
resting state and it is again capable of
entering the catalytic cycle and com-
pleting the sulfination. Of note, once
the tri-Pd complex forms, one equiva-
lent of Pd is lost to the transformation.
Related to this, the nature of the cation
of the sulfide salt and solvent dielectric
is very important to the success of this
transformation. That is, the less soluble
the salt the better the performance,
which can be attributed to lowering
sulfide concentration to avoid the
movement of the Pd-NHC complex
into the above described off-cycle sulfi-
nated resting states.
Keywords: homogeneous catalysis ·
palladium · PEPPSI · sulfination
[a] M. Sayah, Prof. M. G. Organ
Department of Chemistry, York University
4700 Keele Street, Toronto, Ontario M3J 1P3 (Canada)
Fax: (+1)416-736-5936
E-mail: organ@yorku.ca
[b] Dr. A. J. Lough
Department of Chemistry
University of Toronto 80 St. George Street
Toronto, Ontario M5S 3H6 (Canada)
[**] PEPPSI=Pyridine-enhanced precatalyst preparation stabilisation and
initiation.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203142.
Figure 1. Putative catalytic cycle for Pd-catalysed sulfination.
Chem. Eur. J. 2013, 00, 0 – 0 2013 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim
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1
FULL PAPER
2. catalyst preparation stabilisation and initiation; IPent=1,3-
bis(2,6-diisopentylphenyl)imidazol-2-ylidene) was highly ef-
fective for sulfinating strongly deactivated substrates at
room temperature, although precatalyst activation with
Bu2Mg, morpholine or isopropoxide was necessary.[5]
Preca-
talyst activation appeared not to be necessary with phos-
phane ligands and encouraged us to look deeper at the elec-
tronic and steric parameters of the ligands on Pd. We inves-
tigated the challenging coupling of thiophenol (10) to the
hindered oxidative addition partner 9 (Scheme 1). Beginning
our study with the IPr NHC core (IPr=1,3-bis(2,6-diisopro-
pylphenyl)imidazol-2-ylidene), we found that heating to
808C with KOtBu was sufficient to activate Pd-PEPPSI-IPr
(12) and drive catalysis without additional additives. When
the 3-chloropyridine-based PEPPSI precatalyst system was
designed, we expected that the electronegative chlorine
would assist in dissociating the pyridine moiety.[6]
When we
performed the coupling with the simple pyridine derivative
13, we were surprised to find it was consistently activated at
a temperature 108C lower than catalyst 12.[7]
Interestingly,
introducing a substituent at the 4-position of the pyridyl
moiety (14–17), even an electron-withdrawing one (e.g., 17)
completely suppressed precatalyst activation. In another in-
teresting twist, introduction of substituents at the 2-position,
even an electron-donating one (18),showed good reactivity,
although, adding an additional substituent to the 4-position
(19) proved detrimental. When both ortho positions were
occupied by methyl groups, the activation temperature drop-
ped by an additional 108C (20). Presuming that precatalyst
activation is preceded by exchange of the two chlorides to
sulfides (vide infra), the increased bulk can be viewed to
have two divergent effects.[8]
Bulk at the ortho position
could slow ligand exchange to the larger sulfide that could
impact activation overall, but this was not observed. Con-
versely, the increased bulk could drive disulfide RE and pro-
mote precatalyst activation. Electronically, the placement of
substituents, even electron-donating ones, appear to reduce
bond order between the palladium and nitrogen atoms be-
cause the bulk of the substituent elongates this coordinate
bond, rendering the metal more electrophilic, and thus pos-
sibly more likely to undergo reduction (see Table 1 and
Figure 2 for crystal structures of key disulfide resting
states).[8]
Similarly, the PdÀS bond length is longer with
ortho-substituted pyridine complexes, also facilitating RE of
disulfide. With these thoughts in mind we made two addi-
tional modifications to the IPr scaffold. Further increasing
the bulk at the ortho-positions from methyl to ethyl (21)
shut down catalyst activation entirely. Conversely, placement
of chlorine atoms on the NHC backbone (22) lowered the
activation temperature by an additional ten degrees to
508C. It is tempting to suggest that this additional boost in
reactivity is solely due to electronic factors, but the chlorine
atoms also push the N-aryl groups inward toward Pd, mean-
ing that they could have a steric role, despite the distance
from the Pd centre.[9]
Given that Pd-PEPPSI-IPent was found to be much more
reactive than the IPr derivatives in previously reported cou-
pling reactions,[5,10]
we shifted attention to modifications of
the IPent platform. While the simple pyridine derivative
(23) did not show greatly improved activation relative to 13,
the mono-ortho-methyl derivative (25) reduced the activa-
tion temperature to 508C. In addition to the increased size
of the N-phenyl substituent itself, further increasing the
Scheme 1. Sulfination of 2-bromo-1,3-dimethylbenzene (9) with thiophe-
nol (10) using a variety of Pd-PEPPSI complexes without activators at
different temperatures.
Table 1. Effect of ligated pyridine motif on PdÀS, PdÀN and PdÀC bond
lengths of resting states 28 and 29 derived from precatalysts 13 and 20,
respectively. For ORTEP representation of crystal structures 28 and 29
see Figure 2.
PdÀS bond [Š] PdÀN bond [Š] PdÀC bond [Š]
28 2.333 2.077 1.978
29 2.347 2.096 1.985
www.chemeurj.org 2013 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim Chem. Eur. J. 0000, 00, 0 – 0
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2
3. bulk on the pyridine (26) rendered the complex less active.
Finally, as was observed with the IPr platform, chlorinating
the NHC backbone led to optimal precatalyst 27[11]
that
could be smoothly activated at 408C without the aid of any
additive to promote PdII
reduction.
In order to gain additional insight into the mechanism of
activation, we followed the reaction with stoichimetric pre-
catalyst 13 by 1
H NMR spectroscopy (Scheme 2a).[12]
By
keeping the temperature below that which is necessary for
reduction (i.e., RT), we could follow the rapid conversion of
13 to disulfide 28. We then took 28, which is stable and can
be purified by column chromatography, and subjected it to
the reaction conditions from Scheme 1 and near quantitative
sulfination was observed. These experiments confirm that
the dichloro precatalysts first undergo rapid ligand exchange
to the disulfide (e.g., 28) and it is this species that undergoes
reduction and enters the main catalytic cycle.
When the reaction mixture containing stoichiometric pre-
catalyst 13 from the NMR experiment was left to stand, two
visibly different crystals formed. Careful separation of these
crystals, followed by X-ray analysis confirmed the structures
of revealed complex 28 (Figure 2) and tripalladium complex
30, which we could then identify and track by 1
H NMR
spectroscopy.[13]
This interesting tripalladium species, which
has lost one NHC, has no catalytic activity as these crystals
failed to produce any sulfinated product under the reaction
conditions (Scheme 2b, ii). However, when additional pyri-
dine or KOEt (Scheme 2b, iii and iv) was added to the reac-
tion, 30 was broken down liberating NHC–PdACHTUNGTRENNUNG(SPh)2, pre-
sumably, which then completes the reaction.
While diphenyldisulfide is suggested to be susceptible to
reduction under sulfination conditions,[4]
its presence, how-
ever brief, could shift the equilibrium back to the more
stable PdII
complex (e.g., Figure 1). To examine this, preca-
talyst 13 was reduced with one equivalent of dibutylmagne-
sium, immediately followed by addition of ditolyldisulfide
[TolSSTol; all at 08C, Eq. (1)]. The sequence was monitored
Figure 2. ORTEP representation of crystal structures 28 (top) and 29
(bottom) with ellipsoids drawn at the 30% level; hydrogen atoms omit-
ted for clarity.
Scheme 2. Pd complexes formed from interactions with phenylsulfide.
ORTEP representation of the crystal structure of 30 (ellipsoids drawn at
the 30% level).[8]
Chem. Eur. J. 2013, 00, 0 – 0 2013 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim www.chemeurj.org
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3
FULL PAPER
Sulfination by Using Pd-PEPPSI Complexes
4. by 1
H NMR spectroscopy and in the end 32 was isolated
(60%).[12]
Conversely, when 32 by itself was heated to
1008C no disulfide was observed, although approximately
half of it underwent RE of the carbene to produce 34. To
confirm that Pd0
is formed from 32 under our sulfination
conditions, 33 was added to the reaction to trap the active
catalyst (31) as complex 35. In the absence of base, the start-
ing materials were recovered. However, when KOtBu was
used, intermediate 35 was observed with 34 accounting for
the mass balance. When lithium isopropoxide was added in
addition to KOtBu to ensure complete reduction of 32,
quantitative conversion to 35 was observed. So, in the sulfi-
nation process precatalyst 13 gives rise to 32 in situ that re-
ductively eliminates disulfide to produce the active NHC–
Pd0
complex 31, which then enters the catalytic cycle.
When the sulfination reactions carried out in this study
proceeded well, the physical appearance of the mixture
throughout the course of the reaction followed a pattern.
Potassium thiolate is insoluble in toluene, leading to a
highly heterogeneous mixture that was a challenge to stir at
the beginning, but gradually became fully homogeneous as
the reaction progressed. The choice of cation is known to be
important in amination reactions, so we evaluated different
thiolate salts. The sodium salt, which was similarly insoluble,
failed to provide any sulfinated product at 708C, but when
heated to 908C led to 40% conversion (Table 2, entry 2).
Conversely, the lithium salt failed to form any product
(entry 3), but unlike the potassium or sodium thiolates, was
fully soluble. As solubility may play a key role, we examined
other solvents. In every case in which the potassium thiolate
was soluble (Table 2, entries 5–8), sulfination failed to pro-
ceed at all. To ensure that this was not a consequence of the
precatalyst failing to activate, the reaction in DMSO was
pre-activated with Bu2Mg and only trace product was ob-
served (entry 6). Furthermore, we know that our standard
sulfination conditions in DMSO reduce 32 as we were able
to isolate 35 as shown in Equation (2).
Key to the success of sulfination is the presence of butox-
ide base. Reduction of the dithiane by butoxide introduces
more active catalyst into the catalytic cycle and helps to pre-
vent movement of the equilibrium back toward 32. Activa-
tion of resting state 30 does not occur thermally (Scheme 2b,
ii), only when either pyridine or KOEt (Scheme 2b, iii and
iv) was added, suggesting that butoxide is too hindered to
break down 30, which liberates NHC–PdACHTUNGTRENNUNG(SPh)2. Nonethe-
less, when Bu2Mg-activated 13 was reacted with pre-formed
potassium thiolate, the reaction was sluggish [Eq. (3) path
ii]. However, when a catalytic amount of butoxide was
added, the reaction proceeded quantitatively [Eq. (3) pa-
th iii]. With KSPh already in the flask, this clearly points to
an additional role for butoxide, which we attribute to cata-
lyst activation and the continuous reduction of any dithiane
that forms.
Conclusion
In this report we have systematically designed a series of
highly active NHC-based precatalysts specific for sulfina-
tion. In amination studies, 12 activates spontaneously at
room temperature and couples aniline nucleophiles with
high efficiency under identical reaction conditions (toluene,
KOtBu)[10a]
verifying the unique off-cycle poisoning that
faces sulfination. Soluble thiolate salts in toluene, such as
LiSAr, or the use of high dielectric solvents such as N-
methyl-2-pyrrolidone (NMP) or DMSO, suppresses the
transformation. We believe that the low solubility and there-
fore, the low concentration of the thiolate ion in solvents
such as toluene, is essential for good reactivity.
Table 2. Effect of cation and solvent on sulfination using precatalyst 13.
Solvent Cation [M] Appearance Result
1 toluene K heterogeneous 100% conv.
2 toluene Na heterogeneous NR[a]
3 toluene Li fully soluble NR
4 THF K heterogeneous 35% conv.[b]
5 DMSO K fully soluble NR
6 DMSO K fully soluble NR[c]
7 NMP[d]
K fully soluble NR
8 isopropanol K fully soluble trace
[a] Reaction did not proceed at 708C, but did proceed to 40% conversion
when heated to 908C. [b] When the reaction was run for 48 h, 60% con-
version was observed. [c] When catalyst 13 was pre-activated with Bu2Mg
the reaction proceeded to 15% conversion. Again, the mixture was fully
homogeneous.
www.chemeurj.org 2013 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!
4
M. G. Organ et al.
5. Experimental Section
General coupling procedure: In a glovebox, an oven-dried vial (4 mL
screw-cap threaded) equipped with magnetic stir bar was charged with
Pd-PEPPSI catalyst (2 mol%) and KOtBu (60 mg, 2 equiv, 0.5 mmol).
The vial was sealed with a Teflon
-lined screw cap, removed from the
glovebox and 9 (1 equiv, 0.25 mmol) was added by microliter syringe fol-
lowed by toluene (2 mL). Compound 10 (1.2 equiv, 0.3 mmol) was added
dropwise and the reaction was stirred at the indicated temperature for
24 h. At this point the reaction was cooled to room temperature and un-
decane (25 mL) was added. Thereafter a 20 mL aliquot were filtered
through a plug of silica gel and eluted with EtOAc into a GC vial for
GC-MS analysis.
(2,6-Dimethylphenyl)ACHTUNGTRENNUNG(phenyl)sulfane
(11): Following the general procedure,
the reaction was conducted using Pd-
PEPPSI precatalyst 27 (4.8 mg,
2 mol%) at 408C for 24 h. After chro-
matography (pentane, Rf =0.3)(2,6-
dimethylphenyl)ACHTUNGTRENNUNG(phenyl)sulfane (53 mg, 99%) was obtained as a pale-
yellow oil. 1
H NMR (300 MHz, CDCl3): d=7.30–7.19 (m, 5H), 7.10 (t,
J=7.2 Hz, 1H), 6.97 (d, J=7.2 Hz, 2H), 2.47 ppm (s, 6H). Spectral data
were in accordance with those reported in the literature.[14]
General procedure for the synthesis of complexes 12–21 starting from the
chloro-bridged NHC-IPr Dimer: An oven-dried vial (4 mL screw-cap
threaded) equipped with magnetic stir bar was charged with the dimer
(50 mg, 0.044 mmol). The vial was sealed with a Teflon
-lined screw cap
and the indicated pyridine derivative (2 equiv) was added by syringe
under argon followed by CH2Cl2 (1 mL). The solution was stirred at the
indicated temperature and time, whereupon it was filtered through a
small plug of silica and eluted with CH2Cl2 (4 mL). Solvent was removed
under reduced pressure to afford pure product in all cases.
Synthesis of complex 12: Following
the general procedure with meta-chlor-
opyridine (10 mg, 0.088 mmol), the re-
action was stirred at room tempera-
ture for 1 h providing 12 (57 mg, 95%)
as a yellow powder. Spectral data
were in accordance with those report-
ed in the literature.[7]
Synthesis of complex 13: Following
the general procedure with pyridine
(7 mg, 0.088 mmol), the reaction was
stirred at room temperature for 1 h
providing 13 (57 mg, 98%) as a yellow
powder. Spectral data were in accord-
ance with those reported in the litera-
ture.[7]
Synthesis of complex 14: Following
the general procedure with para-meth-
ylpyridine (8.2 mg, 0.088 mmol), the
reaction was stirred at room tempera-
ture for 1 h providing 14 (57 mg, 98%)
as a yellow powder. M.p. 3008C
(decomp); 1
H NMR (300 MHz,
CDCl3): d=8.39 (d, J=4.8 Hz, 2H),
7.51 (t, J=7.8 Hz, 2H), 7.37 (d, J=7.8 Hz, 4H), 7.14 (s, 2H), 6.91 (d, J=
4.8 Hz, 2H), 3.19 (sept, J=6.9 Hz, 4H), 2.23 (s, 3H), 1.50 (d, J=6.9 Hz,
12H), 1.14 ppm (d, J=6.9 Hz, 12H); 13
C NMR (100 MHz, CDCl3): d=
155.2, 150.6, 149.1, 146.5, 135.0, 130.1, 127.9, 127.7, 127.5, 124.8, 124.7,
123.9, 28.6, 26.2, 23.1, 20.8 ppm; HRMS (ES): m/z calcd for
C66H86Cl4N6NaPd2 [2MM+ Na]+
: 1332.4081; found: 1332.4056.
Synthesis of complex 15: Following
the general procedure with para-me-
thoxypyridine (9.6 mg, 0.088 mmol),
the reaction was stirred at room tem-
perature for 1 h providing 15 (57.5 mg,
97%) as a pale-yellow powder. M.p.
2158C (decomp); 1
H NMR (300 MHz,
CDCl3): d=8.38 (d, J=6.4 Hz, 2H),
7.51 (t, J=7.6 Hz, 2H), 7.36 (d, J=
7.6 Hz, 4H), 7.13 (s, 2H), 6.60 (d, J=6.4 Hz, 2H), 3.75 (s, 3H), 3.20
(sept, J=6.8 Hz, 4H), 1.50 (d, J=6.8 Hz, 12H), 1.13 ppm (d, J=6.8 Hz,
12H); 13
C NMR (100 MHz, CDCl3): d=166.3, 155.3, 152.3, 146.6, 135.1,
130.2, 124.9, 124.0, 109.9, 55.5, 28.7, 26.3, 23.2 ppm; HRMS (EI): m/z
calcd for C33H43ClN3OPd [MÀCl]+
: 638.2129; found: 638.2131.
Synthesis of complex 16: Following
the general procedure with para-N,N-
dimethylypyridine (10.8 mg,
0.088 mmol), the reaction was stirred
at room temperature for 1 h providing
16 (58 mg, 97%) as a yellow powder.
M.p. 2858C (decomp); 1
H NMR
(300 MHz, CDCl3): d=8.07 (d, J=
6.6 Hz, 2H), 7.49 (t, J=7.5 Hz, 2H),
7.35 (d, J=7.5 Hz, 4H), 7.11 (s, 2H), 6.22 (d, J=6.6 Hz, 2H), 3.22 (sept,
J=6.8 Hz, 4H), 2.89 (s, 3H), 1.50 (d, J=6.8 Hz, 12H), 1.13 ppm (d, J=
6.8 Hz, 12H); 13
C NMR (100 MHz, CDCl3): d=156.8, 154.2, 150.1, 146.6,
135.2, 129.9, 124.7, 123.9, 106.2, 38.9, 28.6, 26.2, 23.2 ppm; HRMS (EI):
m/z calcd for C34H46ClN4Pd [MÀCl]+
: 651.2446; found: 651.2437.
Synthesis of complex 17: Following the
general procedure with para-trifluoro-
methylpyridine (13 mg, 0.088 mmol),
the reaction was stirred at room tem-
perature for 16 h providing 17 (62 mg,
99%) as a yellow powder. M.p.
3008C (decomp); 1
H NMR
(400 MHz, CD2Cl2): d=8.90 (d, J=
5.6 Hz, 2H), 7.56 (t, J=7.6 Hz, 2H),
7.46–7.40 (m, 6H), 7.22 (s, 2H), 3.18 (sept, J=6.4 Hz, 4H), 1.48 (d, J=
6.4 Hz, 12H), 1.15 ppm (d, J=6.4 Hz, 12H); 13
C NMR (75 MHz, CDCl3):
d=153.2, 152.6, 146.6, 139.3 (q, J=34.5 Hz), 134.9, 130.3, 125.1, 124.0,
119.9, 119.8, 28.7, 26.3, 23.2 ppm; HRMS (EI): m/z calcd for
C33H40ClF3N3Pd [MÀCl]+
: 676.1897; found: 676.1917.
Synthesis of complex 18: Following
the general procedure with ortho-
methylpyridine (8.2 mg, 0.088 mmol),
the reaction was stirred at room tem-
perature for 1 h providing 18 (56 mg,
97%) as a yellow powder. M.p. 1958C
(decomp); 1
H NMR (400 MHz,
CDCl3): d=8.24 (brs, 1H), 7.55 (brs,
2H), 7.41 (brs, 5H), 7.17 (brs, 2H),
6.96 (brs, 2H), 3.19 (brs, 4H), 2.57 (s, 3H), 1.48 (brs, 12H), 1.13 ppm
(brs, 12H); 13
C NMR (100 MHz, CDCl3): d=159.2, 157.1, 150.2, 146.9,
136.8, 135.2, 135.1, 135.0, 130.1, 125.2, 124.8, 123.7, 121.4, 28.7, 26.3, 24,9,
23.1, 22.6 ppm; HRMS (ES): m/z calcd for C33H44Cl2N3Pd [M+H]+
:
660.1943; found: 660.1923.
Synthesis of complex 19: Following
the general procedure with 2,4-dime-
thylpyridine (9.5 mg, 0.088 mmol), the
reaction was stirred at room tempera-
ture for 1 h providing 19 (57 mg, 96%)
as a yellow powder. M.p. 2248C
(decomp); 1
H NMR (300 MHz,
CDCl3): d=8.06 (brs, 1H), 7.54 (brs,
Chem. Eur. J. 2013, 00, 0 – 0 2013 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim www.chemeurj.org
These are not the final page numbers! ÞÞ
5
FULL PAPER
Sulfination by Using Pd-PEPPSI Complexes
6. 2H), 7.41 (brs, 4H), 7.16 (brs, 2H), 6.81 (brs, 2H), 3.19 (brs, 4H), 2.51
(brs, 3H), 2.16 (brs, 3H), 1.48 (brs, 12H), 1.13 ppm (brs, 12H);
13
C NMR (75 MHz, CDCl3): d=158.6, 157.6, 157.4, 156.2, 150.2, 149.7,
148.5, 147.8, 146.9, 137.8, 135.3, 135.2, 135.1, 135.0, 131.1, 130.1, 126.1,
124.8, 123.8, 122.6, 121.7, 28.7, 26.4, 24.7, 24.4, 23.2, 22.9, 22.7, 22.6, 20.7,
17.9 ppm; HRMS (ES): m/z calcd for C34H46Cl2N3Pd [M+H]+
: 672.2104;
found: 672.2111.
Synthesis of complex 20: Following
the general procedure with 2,6-dime-
thylpyridine (9.5 mg, 0.088 mmol), the
reaction was stirred at room tempera-
ture for 4 h providing 20 (59 mg, 99%)
as a yellow powder. Spectral data
were in accordance with those report-
ed in the literature.[7]
Synthesis of complex 21: Following the
general procedure with 2,6-diethypyri-
dine (12 mg, 0.088 mmol), the reaction
was stirred at 408C for 16 h providing
21 (59 mg, 95%) as a yellow powder.
M.p. 3008C (decomp); 1
H NMR
(300 MHz, CDCl3): d=7.58 (t, J=
8.1 Hz, 2H), 7.45–7.37 (m, 5H), 7.20 (s, 2H), 6.82 (d, J=7.8 Hz, 2H),
3.31–3.17 (m, 8H), 1.43 (d, J=7.2 Hz, 12H), 1.11 (d, J=7.2 Hz, 12H),
1.02 ppm (t, J=7.5 Hz, 6H); 13
C NMR (75 MHz, CDCl3): d=163.5,
158.2, 147.4, 137.5, 135.1, 130.0, 124.8, 123.6, 120.1, 31.3, 28.8, 26.6, 22.5,
12.5 ppm; HRMS (ES): m/z calcd for C36H50Cl2N3Pd [M+H]+
: 700.2417;
found: 700.2434.
General procedure for the synthesis of complexes 22–27: An oven-dried
vial (4 mL screw-cap threaded) equipped with magnetic stir bar was
charged with the indicated imidazolium chloride salt (1 equiv, 0.1 mmol),
Cs2CO3 (5 equiv, 164 mg, 0.5 mmol) and pyridine derivative (1 mL) that
served as the solvent. The vial was sealed with a Teflon
-lined screw cap,
and the reaction was stirred at 908C for 24 h. At that time the mixture
was filtered through a small plug of silica (eluted with CH2Cl2 (5 mL)).
The filtrate was concentrated to 0.5 mL under reduced pressure and
loaded onto a silica column and flashed using the indicated eluent
system.
Synthesis of complex 22: Following
the general procedure, the reaction
was conducted using IPrCl
·HCl
(49.5 mg, 0.1 mmol) and 2,6-dimethyl-
pyridine providing 22 (31 mg, 41%) as
a yellow powder following column
chromatography (pentane/CH2Cl2 1:1,
Rf =0.2). M.p. 2158C (decomp);
1
H NMR (400 MHz, CDCl3): d=7.61 (d, J=7.6 Hz, 2H), 7.45 (t, J=
7.6 Hz, 4H), 7.30 (t, J=7.6 Hz, 1H), 7.78 (d, J=7.6 Hz, 2H), 3.07 (sept,
J=6.4 Hz, 4H), 2.57 (s, 6H), 1.46 (d, J=6.4 Hz, 12H), 1.20 ppm (d, J=
6.4 Hz, 12H); 13
C NMR (75 MHz, CDCl3): d=162.6, 158.8, 148.1, 137.5,
132.2, 130.9, 124.4, 122.3, 120.2, 28.9, 25.5, 24.9, 24.3 ppm; HRMS (EI):
m/z calcd for C34H43Cl3N3Pd [MÀCl]+
: 704.1557; found: 704.1543.
Synthesis of complex 23: Following
the general procedure, the reaction
was conducted using IPent·HCl
(54 mg, 0.1 mmol) and pyridine pro-
viding 23 (60.6 mg, 80%) as a yellow
powder following column chromatog-
raphy (pentane/CH2Cl2 5:1, Rf =0.31).
M.p. 1618C (decomp); 1
H NMR
(300 MHz, CDCl3): d=8.59 (d, J=
5.4 Hz, 2H), 7.54 (t, J=7.8 Hz, 1H), 7.46 (t, J=7.5 Hz, 2H), 7.24 (brs,
4H), 7.12–7.07 (m, 4H), 2.84 (m, 4H), 2.17 (m, 4H), 1.88 (m, 4H), 1.58
(sept, J=7.2 Hz, 8H), 1.15 (t, J=7.2 Hz, 12H), 0.84 ppm (t, J=7.2 Hz,
12H); 13
C NMR (75 MHz, CDCl3): d=153.6, 151.4, 144.6, 137.2, 136.7,
129.0, 125.2, 123.9, 41.1, 28.7, 27.1, 12.9, 11.1 ppm; HRMS (ES): m/z
calcd for C40H58Cl2N3Pd [M+H]+
: 756.3043; found: 756.3057.
Synthesis of complex 24: Following
the general procedure, the reaction
was conducted using IPent·HCl
(54 mg, 0.1 mmol) and para-methylpyr-
idine providing 24 (64 mg, 83%) as a
yellow powder following column chro-
matography (pentane/CH2Cl2 5:1, Rf =
0.31). M.p. 1918C (decomp); 1
H NMR
(300 MHz, CDCl3): d=8.42 (d, J=
5.7 Hz, 2H), 7.45 (t, J=7.5 Hz, 2H), 7.25 (d, J=7.5 Hz, 4H), 7.07 (s,
2H), 6.90 (d, J=5.7 Hz, 2H), 2.83 (m, 4H), 2.23 (s, 3H), 2.14 (m, 4H),
1.87 (m, 4H), 1.55 (m, 8H), 1.12 (t, J=7.2 Hz, 12H), 0.79 ppm (t,
J=7.2 Hz, 12H); 13
C NMR (75 MHz, CDCl3): d=154.1, 150.7, 148.9,
144.6, 136.7, 129.0, 125.2, 124.7, 41.1, 28.7, 27.1, 20.8, 12.9, 11.1 ppm;
HRMS (ES): m/z calcd. for C41H60Cl2N3Pd [M+H]+
: 770.3199; found:
770.3246.
Synthesis of complex 25: Following
the general procedure, the reaction
was conducted using IPent·HCl
(54 mg, 0.1 mmol) ortho-methylpyri-
dine providing 25 (61 mg, 79%) as a
yellow powder following column chro-
matography (pentane/CH2Cl2 4:1, Rf =
0.30). M.p. 2508C (decomp); 1
H NMR
(300 MHz, CDCl3): d=8.25 (d, J=5.1 Hz, 1H), 7.49 (t, J=7.8 Hz, 2H),
7.39 (t, J=8.1 Hz, 1H), 7.29 (d, J=7.8, 4H), 7.12 (s, 2H), 6.98–6.90 (m,
2H), 2.85 (m, 4H), 2.57 (s, 3H), 2.10 (m, 4H), 1.85 (m, 4H), 1.52 (m,
8H), 1.07 (t, J=7.2 Hz, 12H), 0.78 ppm (t, J=7.2 Hz, 12H); 13
C NMR
(100 MHz, CDCl3): d=159.4, 156.4, 150.4, 145.0, 136.9, 136.7, 136.2,
128.7, 125.2, 124.9, 121.2, 40.5, 27.9, 27.8, 26.2, 25.1, 12.5, 10.4 ppm;
HRMS (ES): m/z calcd for C41H60Cl2N3Pd [M+H]+
: 770.3199; found:
770.3228.
Synthesis of complex 26: Following
the general procedure, the reaction
was conducted using IPent·HCl
(54 mg, 0.1 mmol) and 2,6-dimethyl-
methylpyridine providing 26 (68 mg,
87%) as a yellow powder following
column chromatography (pentane/
CH2Cl2 6:1, Rf =0.35). M.p. 2988C
(decomp); 1
H NMR (300 MHz, CDCl3): d=7.47 (t, J=7.8 Hz, 2H), 7.33–
7.23 (m, 5H), 7.18 (s, 2H), 6.75 (d, J=7.5 Hz, 2H), 2.82 (m, 4H), 2.58 (s,
6H), 2.05 (m, 4H), 1.84 (m, 4H), 1.53 (m, 8H), 1.06 (t, J=7.2 Hz, 12H),
0.78 ppm (t, J=7.2 Hz, 12H); 13
C NMR (75 MHz, CDCl3): d=158.9,
158.3, 145.5, 137.2, 135.7, 128.6, 125.3, 124.8, 122.1, 40.2, 27.2, 25.6, 25.0,
12.3, 9.9 ppm; HRMS (ES) m/z calcd for C42H62Cl2N3Pd [M+H]+
:
784.3356; found: 784.3388.
Synthesis of complex 27: Following the
general procedure, the reaction was
conducted using IPentCl
·HCl (60.6 mg,
0.1 mmol) and ortho-methylpyridine
providing 27 (50 mg, 59%) as a yellow
powder following column chromatog-
raphy (pentane/CH2Cl2 2:1, Rf =0.25).
M.p. 1858C (decomp); 1
H NMR
(400 MHz, CDCl3): d=8.21 (d, J=
6.0 Hz, 1H), 7.54 (t, J=7.6 Hz, 2H), 7.41 (t, J=7.2 Hz, 1H), 7.35 (d, J=
7.6, 4H), 6.99–6.93 (m, 2H), 2.97 (brs, 4H), 2.52 (s, 3H), 2.01–1.85 (m,
8H), 1.73–1.64 (m, 4H), 1.54–1.45 (m, 4H), 1.08 (t, J=7.2 Hz, 12H),
0.82 ppm (t, J=7.2 Hz, 12H); 13
C NMR (100 MHz, CDCl3): d=159.8,
159.3, 150.3, 145.6, 136.9, 133.1, 129.4, 126.3, 125.4, 121.4, 120.7, 40.3,
26.9, 25.8, 24.9, 12.3, 10.3 ppm; HRMS (ES): m/z calcd for C41H58Cl4N3Pd
[M+H]+
: 838.242; found: 838.2454.
General procedure for the synthesis of complexes 28, 29, 30 and 32: In
the glovebox, an oven-dried vial (4 mL screw-cap threaded) equipped
with magnetic stir bar was charged with the corresponding Pd-PEPPSI
complex (1 equiv, 0.15 mmol) and KOtBu (55 mg, 3.1 equiv, 0.465 mmol).
The vial was sealed with a Teflon
-lined screw cap and removed from the
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ÝÝ These are not the final page numbers!
6
M. G. Organ et al.
7. glovebox whereupon the corresponding thiol (3 equiv, 0.45 mmol) was
added followed by toluene (2 mL). The reaction mixture was stirred at
the indicated temperature and time after which the reaction vial was cen-
trifuged and the supernatant transferred to a round bottom flask. The re-
maining solid was washed with toluene (3”1 mL), centrifuging each
time, and the combined supernatant was evaporated under reduced pres-
sure and the residue purified as indicated.
Synthesis of complex 28: Following
the general procedure 13 (97 mg,
0.15 mmol) and 10 (3 equiv,
0.45 mmol) were reacted at room tem-
perature for 2 h. The supernatant ob-
tained from the centrifugation process
was evaporated and the product was
purified by crystallising 29 out of solu-
tion using pentane/CH2Cl2 at À208C, which left 28 in the mother liquor
as a clean product. Solvent removal provided 28 (82 mg, 60%) as a red
powder. M.p. 82–848C; 1
H NMR (400 MHz, CDCl3): d=8.35 (d, J=
4.8 Hz, 2H), 7.43 (t, J=8.0 Hz, 2H), 7.30 (d, J=8.0 Hz, 4H), 7.23 (s,
2H), 7.0 (t, J=8.0 Hz, 1H), 6.50–6.39 (m, 12H), 3.19 (sept, J=8.0 Hz,
4H), 1.50 (d, J=8.0 Hz, 12H), 1.16 ppm (d, J=8.0, 12H); 13
C NMR
(75 MHz, C6D6): d=169.2, 151.7, 147.5, 146.8, 136.7, 135.0, 132.5, 130.0,
126.3, 124.6, 124.1, 122.2, 121.0, 29.3, 26.5, 23.2 ppm; HRMS (EI): m/z
calcd. for C44H53N3S2Pd [M+H]+
: 792.2637; found: 792.2648.
Synthesis of complex 29: Following
the general procedure, 20 (101 mg,
0.15 mmol) and 10 (3 equiv,
0.45 mmol) were reacted at 508C for
18 h. The supernatant obtained from
the centrifugation process was evapo-
rated and the product was purified by
crystallising 29 out of solution using
pentane/CH2Cl2 at À208C, which left 36 in the mother liquor as a clean
product. Solvent removal provided 36 (41 mg, 30%) as a dark-orange
powder. M.p. 140–1438C; 1
H NMR (400 MHz, C6D6): d=7.50–7.39 (m,
6H), 6.74–6.72 (m, 6H), 6.61 (t, J=9.0 Hz, 2H), 6.51 (t, J=9.0 Hz, 4H),
6.26 (t, J=6.0 Hz, 1H), 5.81 (d, J=6.0, 2H), 3.62 (sept, J=6.0 Hz, 4H),
2.59 (s, 6H), 1.71 (d, J=6.0 Hz, 12H), 1.12 ppm (d, J=6.0 Hz, 12H);
13
C NMR (75 MHz, C6D6): d=170.4, 158.2, 147.1, 144.9, 137.2, 135.8,
135.5, 129.8, 128.1, 126.5, 124.9, 123.9, 122.7, 121.2, 29.3, 27.4, 26.5,
22.9 ppm; HRMS (EI): m/z calcd for C40H50N3SPd [MÀSC6H5]+
:
710.2760; found: 710.2770; X-ray crystallographic analysis is included
below.
Synthesis of complex 30: Following the general procedure, 13 (97 mg,
0.15 mmol) and 10 (3 equiv, 0.45 mmol) were reacted at room tempera-
ture for 2 h. The supernatant obtained from the centrifugation process
was evaporated and the product was crystallised from pentane/CH2Cl2,
chilled at À 208C for 1 h to give 29 as a clean product leaving 28 in the
mother liquor. Compound 29 (35 mg, 40%) were isolated as a yellow
powder. M.p. 2838C (decomp); 1
H NMR (400 MHz, CDCl3): d=7.31–
7.26 (m, 4H), 7.16–7.11 (m, 12H), 6.07 (d, J=8.0 Hz, 4H), 6.89–6.79 (m,
14H), 6.37 (brs, 12H), 3.19 (s, J=6.8 Hz, 8H), 1.27 (d, J=6.8, 24H),
1.05 ppm (d, J=6.8, 24H); 13
C NMR (75 MHz, C6D6): d=175.9, 151.9,
148.2, 146.4, 136.2, 132.1, 130.9, 129.3, 127.1, 125.9, 124.2, 123.3, 120.5,
119.3, 28.8, 26.5, 22.4 ppm.
Synthesis of complex 32: Following the general procedure, 13 (97 mg,
0.15 mmol) and tolylthiol (3 equiv, 0.45 mmol) were reacted at room tem-
perature for 1 h. The supernatant obtained from the centrifugation proc-
ess was evaporated and the product was purified by crystallising impuri-
ties from pentane and leaving 31 in
the mother liquor as a clean product.
Solvent removal provided 32 (113 mg,
80%) as a yellow powder. M.p. 88–
908C; 1
H NMR (400 MHz, C6D6): d=
8.83 (d, J=4.0 Hz, 2H), 7.45 (t, J=
8.0 Hz, 2H), 7.39 d, J=8.0 Hz, 4H),
6.86–6.83 (m, 6H), 6.50 (d, J=8.0 Hz, 4H), 6.25 (t, J=4.0 Hz, 1H), 6.02
(t, J=4.0 Hz, 2H), 3.6 (sept, J=8.0 Hz, 4H), 2.0 (s, 6H), 1.85 (d, J=
8.0 Hz, 12H), 1.26 ppm (d, J=8.0 Hz, 12H); 13
C NMR (75 MHz, C6D6):
d=169.7, 151.6, 146.8, 143.6, 136.7, 134.8, 132.4, 129.8, 129.6, 124.7, 124.0,
122.1, 29.2, 26.4, 23.2, 20.5 ppm; HRMS (EI): m/z calcd for C46H56N3S2Pd
[M+H]+
: 820.2950; found: 820.2957.
Preparation of compound 34 from 32:
An oven-dried vial (4 mL screw-cap
threaded) equipped with a magnetic
stir bar was charged with complex 31
(30 mg, 0.031 mmol) followed by
[D6]benzene. The vial was sealed with
a Teflon
-lined screw cap and the heated to 1008C for 16 h. The
1
H NMR spectrum of this transformation indicated 62% conversion of
31 to 33. At this time, the solvent was removed under reduced pressure
and the product was purified using column chromatography (pentane/
EtOAc 30:1, Rf =0.35) providing (12 mg, 59%) as a dark-orange solid.
M.p. 198–2008C; 1
H NMR (300 MHz, CDCl3): d=7.32–7.28 (m, 6H),
6.88 (brs, 3H), 6.70 (d, J=9.0 Hz, 3H), 7.37 (d, J=9.0 Hz, 2H), 5.66 (d,
J=9.0 Hz, 2H), 2.16 (s, 3H), 1.91 (s, 3H), 1.61 (brs, 4H), 1.44 (d, J=
6.0 Hz, 6H), 1.14 (d, J=6.0 Hz, 6H), 0.81 ppm (d, J=6.0 Hz, 12H);
13
C NMR (75 MHz, CDCl3): d=174.7, 146.4, 145.7, 140.8, 136.7, 135.5,
134.0, 133.4, 131.8, 130.7, 129.6, 127.7, 126.7, 125.0, 124.1, 29.7, 28.7, 28.4,
26.2, 23.5, 22.6, 21.0, 20.8 ppm; HRMS (EI): m/z calcd for C34H43N2S
[MÀSC7H7]+
: 511.3146; found: 511.3142.
Reaction between 32 and 33 in the
presence of KOtBu to produce 35
[Eq. (2)]: In the glovebox an NMR
tube was loaded with 31 (100 mg,
0.122 mmol) and KOtBu (72.5 mg,
5 equiv, 0.61 mmol). A septum was
placed on top of the tube and once
outside the glovebox 32 (57 mg,
2 equiv, 0.244 mmol) was added under argon atmosphere followed by
C6D6 (1 mL). The tube was left to stand in an oil bath at 608C for 16 h at
which time a 1
H NMR spectrum was recorded that revealed 22% conver-
sion to 34 had taken place The solvent was removed under reduced pres-
sure and the product was purified by column chromatography (pentane/
diethyl ether 7:1, Rf =0.24) providing 34 (19 mg, 20%) as a dark-yellow
solid. M.p. 171–1738C; 1
H NMR (400 MHz, C6D6): d=9.66 (d, J=5.2 Hz,
1H), 7.43 (d, J=7.6 Hz, 2H), 7.29–7.24 (m, 2H), 7.25–7.07 (m, 8H), 6.89
(s, 2H), 6.79 (d, J=8.0 Hz, 1H), 6.68 (d, J=7.6 Hz, 2H), 6.54 (t, J=
8.0 Hz, 1H), 6.09 (t, J=8.0 Hz, 1H), 3.84 (sept, J=6.8 Hz, 2H), 3.42
(sept, J=6.4 Hz, 2H), 2.19 (s, 3H), 1.89 (d, J=6.8 Hz, 6H), 1.24 (d, J=
6.8 Hz, 6H), 1.16 (d, J=6.4 Hz, 6H), 1.09 ppm (d, J=6.4 Hz, 6H);
13
C NMR (100 MHz, C6D6): d=181.2, 165.5, 164.0, 151.3, 147.5, 147.4,
147.0, 144.8, 138.3, 136.8, 136.3, 132.3, 129.8, 128.4, 127.6, 124.8, 124.1,
123.9, 123.2, 122.8, 121.2, 117.1, 29.2, 28.4, 26.7, 26.0, 23.1, 22.9, 20.6 ppm;
HRMS (EI): m/z calcd for C38H44N3Pd [MÀC6H5S]+
: 648.2567; found:
648.2589.
Acknowledgements
The authors are grateful to the National Science and Engineering Coun-
cil of Canada (NSERC) and the Ontario Research and Development
Challenge Fund (ORDCF).
Chem. Eur. J. 2013, 00, 0 – 0 2013 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim www.chemeurj.org
These are not the final page numbers! ÞÞ
7
FULL PAPER
Sulfination by Using Pd-PEPPSI Complexes
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[8] For the crystal structure of the disulfide complex derived from 12,
and key structural information (e.g., bond lengths), see the Support-
ing Information. CCDC-898001, 898000 (28) and 898002 (29) con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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[12] For reaction conditions used in the NMR studies, see the Supporting
Information.
[13] When the reaction was performed under the same conditions but
for 30 min instead of 2 h, only 28 was formed as determined by
1
H NMR spectroscopy. Therefore, the formation of 28 and 30 show
time dependency, that is, 28 forms first and then 30 starts to form,
apparently from 28.
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Received: September 5, 2012
Published online: , 0000
www.chemeurj.org 2013 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ These are not the final page numbers!
8
M. G. Organ et al.
9. Pd-Catalysed Sulfination
M. Sayah, A. J. Lough,
M. G. Organ* .................... —
Sulfination by Using Pd-PEPPSI
Complexes: Studies into Precatalyst
Activation, Cationic and Solvent
Effects and the Role of Butoxide Base
On activation duty: The activation of
PEPPSI precatalysts has been evalu-
ated in the sulfination of aryl halides
(see figure). Substitution of the two
chlorides on Pd with two sulfides
occurs immediately, even at low tem-
perature, and it is this species that is
reduced and enters the catalytic cycle.
Butoxide base is involved in precata-
lyst activation and maintaining a
healthy level of active catalyst to
ensure high catalytic performance.
Examination of the cation of the sul-
fide salt and solvent dielectric revealed
that solubility is very important to the
success of this transformation.
Chem. Eur. J. 2013, 00, 0 – 0 2013 Wiley-VCH Verlag GmbH Co. KGaA, Weinheim www.chemeurj.org
These are not the final page numbers! ÞÞ
9
FULL PAPER
Sulfination by Using Pd-PEPPSI Complexes