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.
Oxidative addition is a process where a metal complex increases its oxidation state and coordination number by addition of two ligands. It is the reverse of reductive elimination. It requires the metal to have available orbitals and be in a lower oxidation state. There are four mechanisms for oxidative addition: concerted, SN2, radical, and ionic. Oxidative addition and reductive elimination are important steps in many catalytic cycles in organometallic chemistry and homogeneous catalysis.
This document discusses applications of frontier molecular orbital theory, including cycloaddition reactions, sigma-tropic reactions, and electrocyclic reactions. Cycloaddition reactions like the Diels-Alder reaction can be predicted by Woodward-Hoffmann rules and frontier molecular orbital theory. Sigma-tropic reactions involve breaking a sigma bond and forming a new sigma bond with pi electron rearrangement. Electrocyclic reactions involve opening or closing a ring through conversion of sigma to pi bonds or vice versa. Frontier molecular orbital theory can be used to understand the orbital interactions in these pericyclic reactions. However, the theory has limitations and may not accurately predict reactivity in all cases.
Seminar about the revolutionary impact given by the Pd catalysis to organic synthesis and, as consequence, to medicinal chemistry and drug discovery. A tribute to three amazing Nobel Prizes and a little bit of my personal experience....
Cucurbituril[7] Host - Viologen Guest Complexes: Electrochromic and Photochem...Marina Freitag
The document outlines Marina Freitag's Ph.D. defense presented on Sep 28th 2011. It discusses three topics: 1) Electrochromic properties of viologen cucurbituril complexes. Viologens like methylviologen were encapsulated in cucurbit[7]uril and bound to TiO2 films for use in electrochromic devices. 2) Synthesis of alkyl and aryl viologen derivatives for inclusion in cucurbituril. 3) Fluorescence properties of tolyl-viologen derivatives and their encapsulation and binding in cucurbituril, characterized using NMR and emission titration. The encapsulation prevented aggregation and quenching, and modulated the photophysical properties
Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. They were first synthesized in 1868 by passing carbon monoxide over platinum. Metal carbonyls typically obey the 18 electron rule and are often diamagnetic. They have applications as catalysts in organic synthesis and in producing pure metals like nickel. Precautions must be taken when using metal carbonyls due to their toxicity.
Oxidative addition is a process where a metal complex increases its oxidation state and coordination number by addition of two ligands. It is the reverse of reductive elimination. It requires the metal to have available orbitals and be in a lower oxidation state. There are four mechanisms for oxidative addition: concerted, SN2, radical, and ionic. Oxidative addition and reductive elimination are important steps in many catalytic cycles in organometallic chemistry and homogeneous catalysis.
This document discusses applications of frontier molecular orbital theory, including cycloaddition reactions, sigma-tropic reactions, and electrocyclic reactions. Cycloaddition reactions like the Diels-Alder reaction can be predicted by Woodward-Hoffmann rules and frontier molecular orbital theory. Sigma-tropic reactions involve breaking a sigma bond and forming a new sigma bond with pi electron rearrangement. Electrocyclic reactions involve opening or closing a ring through conversion of sigma to pi bonds or vice versa. Frontier molecular orbital theory can be used to understand the orbital interactions in these pericyclic reactions. However, the theory has limitations and may not accurately predict reactivity in all cases.
Seminar about the revolutionary impact given by the Pd catalysis to organic synthesis and, as consequence, to medicinal chemistry and drug discovery. A tribute to three amazing Nobel Prizes and a little bit of my personal experience....
Cucurbituril[7] Host - Viologen Guest Complexes: Electrochromic and Photochem...Marina Freitag
The document outlines Marina Freitag's Ph.D. defense presented on Sep 28th 2011. It discusses three topics: 1) Electrochromic properties of viologen cucurbituril complexes. Viologens like methylviologen were encapsulated in cucurbit[7]uril and bound to TiO2 films for use in electrochromic devices. 2) Synthesis of alkyl and aryl viologen derivatives for inclusion in cucurbituril. 3) Fluorescence properties of tolyl-viologen derivatives and their encapsulation and binding in cucurbituril, characterized using NMR and emission titration. The encapsulation prevented aggregation and quenching, and modulated the photophysical properties
Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. They were first synthesized in 1868 by passing carbon monoxide over platinum. Metal carbonyls typically obey the 18 electron rule and are often diamagnetic. They have applications as catalysts in organic synthesis and in producing pure metals like nickel. Precautions must be taken when using metal carbonyls due to their toxicity.
Transition metal carbonyls form when carbon monoxide bonds to a transition metal through both sigma and pi bonding. This synergistic metal-ligand bonding strengthens the metal-carbon bond. Metal carbonyls can be classified based on the ligands present and the number/structure of metal atoms. They exhibit a variety of reactions including substitution, reactions with halogens, and disproportionation. Metal carbonyls display properties related to their toxicity, magnetic behavior, thermal stability, and thermodynamic instability.
The selection rules that determine which electronic transitions are allowed or forbidden in transition metal complexes are the Laporte selection rule and spin selection rule. The Laporte rule forbids transitions that result in no change in orbital angular momentum, while the spin rule forbids transitions that change the overall spin of the complex. These rules can be relaxed by vibronic coupling in octahedral complexes or do not apply in tetrahedral complexes. Orbital contributions to paramagnetic moment only occur when the transition metal d orbitals are asymmetrically occupied, allowing electron circulation between degenerate orbitals.
This document discusses methods of organic synthesis, specifically the metathesis of olefins. Metathesis is a reaction where the alkylidene groups of olefins are interchanged, catalyzed by complexes of molybdenum, tungsten, or ruthenium. Examples show olefins converting to mixtures of other olefins. Grubbs catalysts, a series of ruthenium carbene complexes, are also discussed and can tolerate multiple functional groups and solvents. The second generation Grubbs catalyst has higher activity and stability than the first generation.
REDUCTION AND REDUCING AGENTS. in this presentation we explain the
Definition
Identification
Position in periodic table
Examples etc
of reduction and reducing agents.
Organometallic Reactions and CatalysisRajat Ghalta
Organometallic compounds undergo a rich variety of reactions (oxidative addition, reductive elimination, cyclometalization, migratory insertion, carbonylation, hydrometallation hydrate elimination, etc ) that can sometimes be combined into useful homogeneous catalytic cycles. In this presentation, I have discussed organometallic reactions of particular importance for synthetic and catalytic processes like the oxo process (hydroformylation), heck coupling reaction, Wilkinson’s Catalyst
(Hydrogenation) etc.
Biological Applications & Environmental aspects of Organometallic CompoundsRudreshMr
It is the descriptive approach on Applicational aspects of Organometallic Compounds with a higly Interactive e-Content with appropriate links, references....
An approach for designing organic synthesis which involves breaking down of target molecule into available starting material by imaginary breaking of bonds (disconnection) and/or by functional group interconversion is known as disconnection approach or retrosynthesis or synthesis backward.
The C-X disconnection approach is mainly applicable to a carbon chain attached to any of the heteroatoms like O, N, or S. Here, a bond joins the heteroatom (X) to the rest of the molecule like a C-O, C-N, or C-S group. This point is good point to initiate a disconnection. This is called a ‘One-group’ C-X disconnection as one would need to identify only one functional group like ester, ether, amide etc. to make the disconnection.
How to choose a disconnection?
These are the few general strategy which are important points introduced which apply to the whole of synthetic design rather than one particular area. The main choice is between the various disconnection, even such a simple disconnection as the following alcohol can be disconnected.
We want to get back to simple starting materials and we shall do if we disconnect the bond which are:
Towards the middle of the molecule thereby breaking into two reasonably equal halves rather than chopping off one or two carbon atoms from the end and,
At a branch as this is more likely to give straight chain fragments and these are more likely to be available.
Disconnections very often take place immediately adjacent to, or very close to functional groups in the target molecule. This is pretty much inevitable, given that functionality almost invariably arises from the forward reaction.
A simple example is the weedkiller propanil used on rice fields. Amide disconnection gives amine obviously made from o-dichlorobenzene by nitration and reduction. All positions around the ring in o-dichlorobenzene are about the same electronically but steric hindrance will lead to dichloronitrobenzene being the major product
This compound was needed for some research into the mechanisms of rearrangements. We can disconnect on either side of the ether oxygen atom, but (b) is much better because (a) does not correspond to a reliable reaction: it might be hard to control selective alkylation of the primary hydroxyl group in the presence of the secondary one.
The disconnections we have made so far have all been of C–O, C–N, or C–S bonds, but, of course, the most important reactions in organic synthesis are those that form C–C bonds. We can analyze C–C disconnections in much the same way as we’ve analyzed C–X disconnections.
The Zeneca drug propranolol is a beta-blocker that reduces blood pressure and is one of the top drugs worldwide. It has two 1,2-relationships in its structure but it is best to disconnect the more reactive amine group first.
Arildone is a drug that prevents polio and herpes simplex viruses from ‘unwrapping’ their DNA, and renders them harmless.
The document discusses charge transfer complexes and the different types of charge transfer that can cause color in transition metal complexes. It explains that ligand to metal charge transfer and metal to ligand charge transfer can produce color when pi donor or accepting ligands are present with metals lacking or having low oxidation state d-electrons, respectively. As an example, it describes the metal to ligand charge transfer observed in the spectra of the tris(bipyridine)ruthenium(II) dichloride complex.
This document discusses reduction reactions and reducing agents. It aims to teach the reader to: 1) exploit differences in reactivity between hydride and neutral reducing agents to achieve chemoselective reductions; 2) use substrate chirality to control syn vs. anti diastereoselectivity in ketone reductions; 3) rationalize reaction outcomes using transition state diagrams; 4) appreciate the versatility of transition metals in reductions; 5) understand the utility of dissolving metal reductions; and 6) use radical chemistry for deoxygenation and halide reduction. It then provides details on various hydride and neutral reducing agents, focusing on their reactivities and applications in selective reductions.
This document summarizes the Huckel molecular orbital theory. It describes the theory's key postulates for simplifying calculations for pi-electron systems like ethylene. The postulates state that overlap integrals are zero, coulomb integrals are equal, and exchange integrals are non-zero only for adjacent atoms. For ethylene, the HMO calculations yield two energy levels - a bonding and antibonding level. The coefficients and electron density are also calculated for ethylene's bonding orbital. Finally, the bond order and free valence are determined, showing ethylene has one pi-bond and equal reactivity at both carbon atoms.
This document contains answers from an expert to questions on asymmetric synthesis. It addresses predicting major products of reactions based on stereochemistry, identifying the appropriate starting material for synthesizing a target molecule via retrosynthesis analysis and mechanism, and determining whether (Z)- or (E)-enolates would form as major products from reactions with lithium diisopropylamine. The expert provides short answers for multiple choice and theoretical questions relating to stereochemistry and asymmetric synthesis.
This document discusses organometallic compounds and their uses as catalysts in homogeneous and heterogeneous reactions. It provides examples of homogeneous catalysis using organometallic compounds like cobalt carbonyl and rhodium complexes. The mechanisms involve steps like oxidative addition, CO insertion, 1,2-insertion, and reductive elimination. Examples of heterogeneous catalysis on titanium surfaces are also provided. Finally, the document lists references used.
Crown ethers
NOMENCLATURE
GENERAL SYNTHESIS OF CROWN ETHER
AZA CROWN
CRYPTAND
APPLICATIONS
1. SYNTHETIC APPLICTION
Esterification
Saponification
Anhydride formation
Potassium permanganate oxidation
Aromatic substitution reactions
Elimination reactions
Displacement reaction
Generation of carbenes
Superoxide anion
Alkylations – 1. o-alkylations
2. c-alkylations
3. n-alkylations
2. ANALYTICAL APPLICATION
Determination of gold in geological samples
Super critical fluid extraction of trace metal from solid and liquid materials
Application of ionic liquids in analytical chemistry
Oxidation and determination of aldehydes
Crown ethers are used in the laboratory as phase transfer catalyst
OTHER APPLICATION
It is used in photocynation
Resolution of racemic mixture
Benzoin condensation
Hetrocyclisation
Synthesis of furanones
Acetylation of secondary amines in presence of primary amine
This presentation discusses the reactions of organolithium compounds. Organolithium compounds undergo several reactions including: reaction with carbon dioxide to form ketones; reaction with oxygen to form hydroperoxides; reaction with esters and alkyl cyanides to form ketones; and electrophilic displacement reactions with organic halides. Electrophilic displacement, or metal-halogen exchange, is an important reaction as it allows for the synthesis of reactive organolithium compounds like vinyl lithium and phenyl lithium which can be used as precursors in organic synthesis.
Longifolene is common naturally occurring, oily liquid hydrocarbon found in the high boiling fraction of certain pine resins.
Juvabione is a terpene- derived-keto-ester that has been isolated from plant sources.
Morphine is a major component of opium,it is isolated from poppy straw of the opium poppy.
Retrosynthes analysis and disconnection approach ProttayDutta1
Retrosynthetic analysis is a technique used to plan organic syntheses by working backwards from the target molecule. It involves mentally deconstructing the target molecule through sequential disconnections and functional group transformations until commercially available starting materials are reached. Each disconnection produces synthons, which are idealized fragments that represent possible reaction precursors. Common types of disconnections include C-X, C-C, and carbonyl bonds. The goal of retrosynthesis is to simplify the target structure and design multiple possible synthesis routes leading from simple starting materials to the target. It helps chemists discover efficient syntheses by considering the reactivity, selectivity, and availability of materials at each step.
This document summarizes key concepts in organometallic chemistry. It discusses the definition of organometallic compounds as those containing metal-carbon bonds. It outlines different types of ligands that can bind to metals, including carbonyl, carbene, and cyclic π systems. It also describes principles for understanding bonding interactions between ligands and metals, such as the 18-electron rule and molecular orbital theory. Spectroscopic techniques for analyzing organometallic compounds are also summarized.
The homolytic cleavage of covalent bonds in carbonyl compound under photochemical conditions known as Norrish Type Reactions
They are divided into two types
Norrish Type I
Norrish Type II reaction
Gilman's reagent is a lithium and copper (diorganocopper) compound that can be prepared by adding copper(I) iodide to methyllithium at -78°C. Gilman's reagent is useful for replacing halide groups with organic groups through SN2 reactions. Some applications include 1) 1,4-addition to conjugated enones due to the soft nucleophilicity of the reagent, 2) alkyl cross-coupling reactions with organic halides, and 3) addition to acid chlorides to form ketones.
This document discusses hydrocarbons derivatives, which are formed when one or more hydrogen atoms in a hydrocarbon are replaced by other elements or functional groups. It provides examples of common derivatives such as alcohols, haloalkanes, aldehydes, ketones, carboxylic acids, and amines. It also summarizes several chemical reactions these derivatives undergo, such as alcohol oxidation, esterification, and acid-base reactions. Finally, it gives examples of applications for these derivatives in areas like pharmaceuticals, fuels, solvents, flavors, fragrances, and more.
Syngas is a mixture of hydrogen and carbon monoxide produced through gasification processes. It can be used directly as fuel or to synthesize other fuels and chemicals. The main industrial processes for syngas production are steam reforming, autothermal reforming, and partial oxidation of hydrocarbons. Partial oxidation involves reacting hydrocarbons with oxygen without steam, producing syngas at lower costs but higher temperatures than steam reforming. Catalytic partial oxidation uses catalysts to control the reaction and reduce heat generation. Research continues to improve catalyst heat resistance and prevent coking while reducing costs of syngas production.
Transition metal carbonyls form when carbon monoxide bonds to a transition metal through both sigma and pi bonding. This synergistic metal-ligand bonding strengthens the metal-carbon bond. Metal carbonyls can be classified based on the ligands present and the number/structure of metal atoms. They exhibit a variety of reactions including substitution, reactions with halogens, and disproportionation. Metal carbonyls display properties related to their toxicity, magnetic behavior, thermal stability, and thermodynamic instability.
The selection rules that determine which electronic transitions are allowed or forbidden in transition metal complexes are the Laporte selection rule and spin selection rule. The Laporte rule forbids transitions that result in no change in orbital angular momentum, while the spin rule forbids transitions that change the overall spin of the complex. These rules can be relaxed by vibronic coupling in octahedral complexes or do not apply in tetrahedral complexes. Orbital contributions to paramagnetic moment only occur when the transition metal d orbitals are asymmetrically occupied, allowing electron circulation between degenerate orbitals.
This document discusses methods of organic synthesis, specifically the metathesis of olefins. Metathesis is a reaction where the alkylidene groups of olefins are interchanged, catalyzed by complexes of molybdenum, tungsten, or ruthenium. Examples show olefins converting to mixtures of other olefins. Grubbs catalysts, a series of ruthenium carbene complexes, are also discussed and can tolerate multiple functional groups and solvents. The second generation Grubbs catalyst has higher activity and stability than the first generation.
REDUCTION AND REDUCING AGENTS. in this presentation we explain the
Definition
Identification
Position in periodic table
Examples etc
of reduction and reducing agents.
Organometallic Reactions and CatalysisRajat Ghalta
Organometallic compounds undergo a rich variety of reactions (oxidative addition, reductive elimination, cyclometalization, migratory insertion, carbonylation, hydrometallation hydrate elimination, etc ) that can sometimes be combined into useful homogeneous catalytic cycles. In this presentation, I have discussed organometallic reactions of particular importance for synthetic and catalytic processes like the oxo process (hydroformylation), heck coupling reaction, Wilkinson’s Catalyst
(Hydrogenation) etc.
Biological Applications & Environmental aspects of Organometallic CompoundsRudreshMr
It is the descriptive approach on Applicational aspects of Organometallic Compounds with a higly Interactive e-Content with appropriate links, references....
An approach for designing organic synthesis which involves breaking down of target molecule into available starting material by imaginary breaking of bonds (disconnection) and/or by functional group interconversion is known as disconnection approach or retrosynthesis or synthesis backward.
The C-X disconnection approach is mainly applicable to a carbon chain attached to any of the heteroatoms like O, N, or S. Here, a bond joins the heteroatom (X) to the rest of the molecule like a C-O, C-N, or C-S group. This point is good point to initiate a disconnection. This is called a ‘One-group’ C-X disconnection as one would need to identify only one functional group like ester, ether, amide etc. to make the disconnection.
How to choose a disconnection?
These are the few general strategy which are important points introduced which apply to the whole of synthetic design rather than one particular area. The main choice is between the various disconnection, even such a simple disconnection as the following alcohol can be disconnected.
We want to get back to simple starting materials and we shall do if we disconnect the bond which are:
Towards the middle of the molecule thereby breaking into two reasonably equal halves rather than chopping off one or two carbon atoms from the end and,
At a branch as this is more likely to give straight chain fragments and these are more likely to be available.
Disconnections very often take place immediately adjacent to, or very close to functional groups in the target molecule. This is pretty much inevitable, given that functionality almost invariably arises from the forward reaction.
A simple example is the weedkiller propanil used on rice fields. Amide disconnection gives amine obviously made from o-dichlorobenzene by nitration and reduction. All positions around the ring in o-dichlorobenzene are about the same electronically but steric hindrance will lead to dichloronitrobenzene being the major product
This compound was needed for some research into the mechanisms of rearrangements. We can disconnect on either side of the ether oxygen atom, but (b) is much better because (a) does not correspond to a reliable reaction: it might be hard to control selective alkylation of the primary hydroxyl group in the presence of the secondary one.
The disconnections we have made so far have all been of C–O, C–N, or C–S bonds, but, of course, the most important reactions in organic synthesis are those that form C–C bonds. We can analyze C–C disconnections in much the same way as we’ve analyzed C–X disconnections.
The Zeneca drug propranolol is a beta-blocker that reduces blood pressure and is one of the top drugs worldwide. It has two 1,2-relationships in its structure but it is best to disconnect the more reactive amine group first.
Arildone is a drug that prevents polio and herpes simplex viruses from ‘unwrapping’ their DNA, and renders them harmless.
The document discusses charge transfer complexes and the different types of charge transfer that can cause color in transition metal complexes. It explains that ligand to metal charge transfer and metal to ligand charge transfer can produce color when pi donor or accepting ligands are present with metals lacking or having low oxidation state d-electrons, respectively. As an example, it describes the metal to ligand charge transfer observed in the spectra of the tris(bipyridine)ruthenium(II) dichloride complex.
This document discusses reduction reactions and reducing agents. It aims to teach the reader to: 1) exploit differences in reactivity between hydride and neutral reducing agents to achieve chemoselective reductions; 2) use substrate chirality to control syn vs. anti diastereoselectivity in ketone reductions; 3) rationalize reaction outcomes using transition state diagrams; 4) appreciate the versatility of transition metals in reductions; 5) understand the utility of dissolving metal reductions; and 6) use radical chemistry for deoxygenation and halide reduction. It then provides details on various hydride and neutral reducing agents, focusing on their reactivities and applications in selective reductions.
This document summarizes the Huckel molecular orbital theory. It describes the theory's key postulates for simplifying calculations for pi-electron systems like ethylene. The postulates state that overlap integrals are zero, coulomb integrals are equal, and exchange integrals are non-zero only for adjacent atoms. For ethylene, the HMO calculations yield two energy levels - a bonding and antibonding level. The coefficients and electron density are also calculated for ethylene's bonding orbital. Finally, the bond order and free valence are determined, showing ethylene has one pi-bond and equal reactivity at both carbon atoms.
This document contains answers from an expert to questions on asymmetric synthesis. It addresses predicting major products of reactions based on stereochemistry, identifying the appropriate starting material for synthesizing a target molecule via retrosynthesis analysis and mechanism, and determining whether (Z)- or (E)-enolates would form as major products from reactions with lithium diisopropylamine. The expert provides short answers for multiple choice and theoretical questions relating to stereochemistry and asymmetric synthesis.
This document discusses organometallic compounds and their uses as catalysts in homogeneous and heterogeneous reactions. It provides examples of homogeneous catalysis using organometallic compounds like cobalt carbonyl and rhodium complexes. The mechanisms involve steps like oxidative addition, CO insertion, 1,2-insertion, and reductive elimination. Examples of heterogeneous catalysis on titanium surfaces are also provided. Finally, the document lists references used.
Crown ethers
NOMENCLATURE
GENERAL SYNTHESIS OF CROWN ETHER
AZA CROWN
CRYPTAND
APPLICATIONS
1. SYNTHETIC APPLICTION
Esterification
Saponification
Anhydride formation
Potassium permanganate oxidation
Aromatic substitution reactions
Elimination reactions
Displacement reaction
Generation of carbenes
Superoxide anion
Alkylations – 1. o-alkylations
2. c-alkylations
3. n-alkylations
2. ANALYTICAL APPLICATION
Determination of gold in geological samples
Super critical fluid extraction of trace metal from solid and liquid materials
Application of ionic liquids in analytical chemistry
Oxidation and determination of aldehydes
Crown ethers are used in the laboratory as phase transfer catalyst
OTHER APPLICATION
It is used in photocynation
Resolution of racemic mixture
Benzoin condensation
Hetrocyclisation
Synthesis of furanones
Acetylation of secondary amines in presence of primary amine
This presentation discusses the reactions of organolithium compounds. Organolithium compounds undergo several reactions including: reaction with carbon dioxide to form ketones; reaction with oxygen to form hydroperoxides; reaction with esters and alkyl cyanides to form ketones; and electrophilic displacement reactions with organic halides. Electrophilic displacement, or metal-halogen exchange, is an important reaction as it allows for the synthesis of reactive organolithium compounds like vinyl lithium and phenyl lithium which can be used as precursors in organic synthesis.
Longifolene is common naturally occurring, oily liquid hydrocarbon found in the high boiling fraction of certain pine resins.
Juvabione is a terpene- derived-keto-ester that has been isolated from plant sources.
Morphine is a major component of opium,it is isolated from poppy straw of the opium poppy.
Retrosynthes analysis and disconnection approach ProttayDutta1
Retrosynthetic analysis is a technique used to plan organic syntheses by working backwards from the target molecule. It involves mentally deconstructing the target molecule through sequential disconnections and functional group transformations until commercially available starting materials are reached. Each disconnection produces synthons, which are idealized fragments that represent possible reaction precursors. Common types of disconnections include C-X, C-C, and carbonyl bonds. The goal of retrosynthesis is to simplify the target structure and design multiple possible synthesis routes leading from simple starting materials to the target. It helps chemists discover efficient syntheses by considering the reactivity, selectivity, and availability of materials at each step.
This document summarizes key concepts in organometallic chemistry. It discusses the definition of organometallic compounds as those containing metal-carbon bonds. It outlines different types of ligands that can bind to metals, including carbonyl, carbene, and cyclic π systems. It also describes principles for understanding bonding interactions between ligands and metals, such as the 18-electron rule and molecular orbital theory. Spectroscopic techniques for analyzing organometallic compounds are also summarized.
The homolytic cleavage of covalent bonds in carbonyl compound under photochemical conditions known as Norrish Type Reactions
They are divided into two types
Norrish Type I
Norrish Type II reaction
Gilman's reagent is a lithium and copper (diorganocopper) compound that can be prepared by adding copper(I) iodide to methyllithium at -78°C. Gilman's reagent is useful for replacing halide groups with organic groups through SN2 reactions. Some applications include 1) 1,4-addition to conjugated enones due to the soft nucleophilicity of the reagent, 2) alkyl cross-coupling reactions with organic halides, and 3) addition to acid chlorides to form ketones.
This document discusses hydrocarbons derivatives, which are formed when one or more hydrogen atoms in a hydrocarbon are replaced by other elements or functional groups. It provides examples of common derivatives such as alcohols, haloalkanes, aldehydes, ketones, carboxylic acids, and amines. It also summarizes several chemical reactions these derivatives undergo, such as alcohol oxidation, esterification, and acid-base reactions. Finally, it gives examples of applications for these derivatives in areas like pharmaceuticals, fuels, solvents, flavors, fragrances, and more.
Syngas is a mixture of hydrogen and carbon monoxide produced through gasification processes. It can be used directly as fuel or to synthesize other fuels and chemicals. The main industrial processes for syngas production are steam reforming, autothermal reforming, and partial oxidation of hydrocarbons. Partial oxidation involves reacting hydrocarbons with oxygen without steam, producing syngas at lower costs but higher temperatures than steam reforming. Catalytic partial oxidation uses catalysts to control the reaction and reduce heat generation. Research continues to improve catalyst heat resistance and prevent coking while reducing costs of syngas production.
The document discusses retrosynthetic analysis, which is a problem-solving technique used in organic synthesis. It involves working backwards from the target molecule and breaking it down into simpler structures through the reverse of known reactions. This allows chemists to plan a synthesis by tracing the target back to commercially available starting materials. The document outlines common disconnections, reactions, and strategies used in retrosynthetic analysis and organic synthesis planning.
The document discusses the derivation of Beer-Lambert's law, which relates the absorption of light to the properties of the material through which the light is passing. Lambert first derived a relationship showing that the decrease in light intensity through a medium is directly proportional to the intensity and thickness of the medium. Beer later extended this by showing absorption also depends on the concentration of the absorbing solution. Together, Beer and Lambert derived an equation, now known as Beer-Lambert's law, that quantifies the relationship between light absorption and intensity, thickness of the medium, and concentration of an absorbing solution. The law has limitations in that it applies only to monochromatic, unscattered light passing through dilute solutions.
1) Wilkinson catalyst, chlorotris(triphenylphosphine)rhodium(I), is an efficient homogeneous catalyst for hydrogenation of alkenes.
2) The mechanism of hydrogenation involves oxidative addition, ligand dissociation, alkene coordination, migratory insertion, ligand association, and reductive elimination steps.
3) The hydrogenation is selective based on sterics and substitution - less substituted and sterically hindered alkenes react first, followed by exocyclic over endocyclic and cis over trans alkenes.
Alkenes readily undergo addition reactions where carbon-carbon double bonds become single bonds. Common addition reactions include bromination, hydrogenation, and combustion. Alkenes are manufactured through cracking of petroleum, which involves breaking down long-chain hydrocarbons into smaller molecules like alkenes over a catalyst at high temperatures. Cracking provides important products for fuels and materials.
Physical and chemical properties of petroleumkhurasani
Petroleum is a naturally occurring liquid found beneath the Earth's surface that is refined into fuels. It consists mainly of hydrocarbons like alkanes, naphthenes, and aromatics. Petroleum forms from the thermal maturation of buried organic matter over millions of years. It varies in composition but is largely made up of carbon and hydrogen, with other elements like sulfur, oxygen, and nitrogen present in smaller amounts. The type of petroleum depends on factors like the organic material it formed from and temperature/pressure conditions during formation.
This dissertation examines theoretical models for cyclone design parameters, including travel distance, number of turns, pressure drop, and collection efficiency. The author develops new models for these parameters based on analysis of particle motion and air flow within the cyclone. Experimental testing is used to validate the theoretical pressure drop model. The effects of particle size distribution and air density on cyclone performance are also investigated. The goal of this research is to improve the accuracy of predicting cyclone performance for particulate control applications.
1. Biological oxidation is the cellular process by which organic substances like carbohydrates, fats, and proteins release energy through redox reactions, producing CO2, H2O, and ATP.
2. In the mitochondria, electrons are transferred through redox carriers in the electron transport chain from NADH or FADH2 to oxygen, driving the pumping of protons across the inner mitochondrial membrane and building an electrochemical gradient.
3. The potential energy of this proton gradient is harnessed by ATP synthase to phosphorylate ADP, coupling electron transport to oxidative phosphorylation and the production of ATP through chemiosmosis.
The document analyzes and compares two types of Dickson charge pump designs: 1) a parallel combination of small charge pumps and 2) a single large charge pump. It discusses the specifications and design parameters that affect the output voltage, current drivability, and power efficiency of each design. Graphs are presented showing the performance metrics for each design type under variations in output voltage, clock period, and input voltage. The document concludes by directly comparing the two designs across these metrics to determine which provides better current drivability and power efficiency for a given chip area.
The Cyclone Engine is built of three major components, the Steam Generator, Piston Block, and Condenser. The working fluid, deionized water, travels continuously through these three components. Beginning in the steam generator, moving into the pistons, then to the condenser, and finally pumped back into the steam generator.
Light absorption enhancement in extremely confined Ge nanostructures Salvo Mirabella
Invited talk at EMRS Spring conference, Lille, France.
How and to which extent quantum confinement affects the light absorption bandgap and efficiency in germanium quantum dots embedded in silica.
PPT ON MANAGEMENT OF CYCLONIC DISASTERShreya Soman
This document discusses the management of cyclones, including:
- Defining cyclones as areas of low atmospheric pressure characterized by inward spiraling winds that rotate counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere.
- Explaining that cyclones are known as hurricanes, typhoons, or cyclones depending on where they occur.
- Detailing the structure and formation of cyclones and categorizing different types including polar, polar low, sub-tropical, and tropical cyclones.
- Identifying major factors for cyclone disasters such as human effects on climate change and global warming, destruction of coastal forests, and poverty exacerbating damage.
- Providing recommendations for prec
1.9 light absorption, reflection and colourQC Labs
The document discusses light absorption, reflection, and color. It defines key terms used in color technology like hue, strength/depth, and brightness/dullness. It explains that hue is determined by the wavelength region where light absorption is strongest. Strength refers to the color yield of a dye. Depth and brightness are also defined. Examples are given of absorption curves for dyes of different colors and how they relate to hue. Methods for measuring dye and pigment strength are outlined. The factors that influence dullness versus brightness in dyes are explained.
The document summarizes advanced oxidation processes (AOPs) for treating food industry wastewater. It discusses four main AOP groups - electrochemical oxidation, Fenton's process, ozonation, and photocatalytic processes. All generate highly reactive hydroxyl radicals to degrade organic pollutants that are resistant to biological treatment. Electrochemical oxidation uses electrodes to produce hydroxyl radicals and has effectively treated various food industry wastewaters. Fenton's process uses ferrous ions and hydrogen peroxide to catalytically produce hydroxyl radicals. Photocatalytic processes employ materials like TiO2 and UV light to generate radicals.
Magnesium and methane undergo oxidation reactions in the examples provided. In the magnesium reaction, magnesium atoms are oxidized when they lose electrons to form magnesium ions. In the methane reaction, hydrogen atoms gain oxygen and are oxidized to form water, while carbon gains oxygen and is oxidized to carbon dioxide. Oxidation causes a loss of electrons or gain of oxygen. Reduction is the opposite, with a gain of electrons or loss of oxygen. Oxidizing agents become reduced by causing other reactants to be oxidized, while reducing agents become oxidized by causing other reactants to be reduced.
Organic chemistry is the study of carbon compounds. Atoms bond together to form molecules, the smallest units that retain a compound's properties. Carbon can form four bonds, allowing it to create large, complex molecules. The bonding between carbon atoms involves the overlap of atomic orbitals, resulting in sigma and pi bonds that determine a molecule's shape and reactivity. Understanding bonding models allows organic chemists to predict and explain the properties of carbon compounds.
1) Cyclones form due to low atmospheric pressure and spiral inward in a counterclockwise direction in the Northern Hemisphere. They are known as hurricanes, typhoons, or cyclones depending on the region.
2) Cyclones form from either cold or warm cores and consist of a northern and southern hemisphere surrounding a low pressure center.
3) Major factors for cyclone disasters include human-caused climate change, destruction of coastal barriers, and poverty exacerbating storm impacts.
Chapter 20.3 : Saturated and Unsaturated HydrocarbonsChris Foltz
The document discusses different types of hydrocarbons:
- Saturated hydrocarbons like alkanes have only single carbon-carbon bonds. Unsaturated hydrocarbons have double or triple bonds.
- Alkanes are named using Greek or Latin prefixes to indicate the number of carbon atoms and the suffix "-ane". Branched alkanes use alkyl groups.
- Alkenes contain double bonds and are named similarly but use the suffix "-ene". Alkynes have triple bonds and use "-yne". Aromatic hydrocarbons have delocalized electrons in six-carbon rings like benzene.
This document provides an introduction to organic chemistry, focusing on hydrocarbons. It defines organic chemistry as the study of carbon-containing compounds, of which over 90% are organic. The key types of hydrocarbons discussed are alkanes (containing only single bonds), alkenes (containing carbon-carbon double bonds), and alkynes (containing carbon-carbon triple bonds). The document outlines methods for naming and drawing structural formulas of straight-chain and branched alkanes, as well as alkenes and alkynes.
Homogeneous catalysis refers to reactions where the catalyst is in the same phase as the reactants. Common homogeneous catalysts include acids and bases in aqueous solutions. Homogeneous catalysts can provide selectivity in terms of chemoselectivity, regioselectivity, diastereoselectivity, and enantioselectivity. Important reaction types for homogeneous catalysis include oxidative addition, reductive elimination, migratory insertion, and β-hydride elimination. Key reactions discussed are hydrogenation, hydroformylation, hydrocyanation, and applications of Ziegler-Natta catalysts and Wilkinson's catalyst. Chiral induction with chiral ligands is also discussed for producing chiral molecules in drug synthesis such as L-DOPA
This document discusses different types of catalysis including homogeneous catalysis, heterogeneous catalysis, and enzyme catalysis. Homogeneous catalysis involves catalysts and reactants in the same phase, while heterogeneous catalysis involves catalysts in a different phase than the reactants. Enzyme catalysis is biologically important and involves enzymes acting as highly specific catalysts within organisms. The mechanisms of these catalysis types and examples such as hydrogenation reactions and catalytic converters are also described.
Catalysts accelerate chemical reactions without being consumed. There are two types of catalysts: homogeneous, where the catalyst is in the same phase as the reactants, and heterogeneous, where the catalyst is in a different phase. In heterogeneous catalysis, the catalyst is typically a solid and the reactants are gases or liquids. The catalyst provides alternative reaction pathways with lower activation energies. Enzymes are biological catalysts that work by binding reactants in cavities on their surfaces, forming activated complexes that decompose into products.
The document discusses the principles and characteristics of catalysts. It begins by defining catalysts as substances that accelerate chemical reactions by lowering activation energy without being consumed. It then discusses several key points about catalysts, including that they: (1) provide alternative reaction pathways with lower activation energies; (2) are regenerated after reactions and only small amounts are needed; and (3) do not change chemical equilibrium but help reactions reach equilibrium faster. The document also outlines general characteristics of catalysts such as specificity, inability to initiate reactions, and achieving maximum activity at an optimum temperature.
This document provides an overview of catalysis by organometallic compounds. It discusses that organometallic compounds are widely used as homogeneous catalysts in industrial processes and research. Nobel Prizes have been awarded for discoveries in organometallic chemistry and homogeneous catalysis. Examples of important organometallic catalysts discussed include Wilkinson's catalyst, Noyori's catalyst for asymmetric hydrogenation, and Ziegler-Natta catalysts for polymerization of olefins. The mechanisms of homogeneous hydrogenation and different types of catalysis such as homogeneous versus heterogeneous are also summarized.
Introduction
Basis
Importance
Classification
Homogeneous catalysis
Mechanism
Example
Heterogeneous catalysis
Mechanism
Examples
Promoters
Catalytic Poisoning
Autocatalysis
Enzyme catalysis
Enzymes
References
Catalyst: -
The substances that alter the rate of a reaction but itself remains chemically unchanged at the end of the reaction is called a Catalyst.
The process is called Catalysis.
prop-
A catalyst cannot start the reaction by itself.
Catalytic activity increases as surface area of catalyst increases.
Catalysts are thermolabile, this effect is very well pronounced in enzymes.
Catalytic activity is maximum at a catalyst’s optimum temperature.
A catalyst does not alter the position of the equilibrium, instead it helps in achieving the equilibrium faster.
Biochemistry 304 2014 student edition enzymes and enzyme kineticsmartyynyyte
Enzyme kinetics and the mechanisms of enzyme catalysis are described. Key points include:
1) Enzymes lower the activation energy of biochemical reactions, increasing rates up to billions of times faster than uncatalyzed reactions. This is achieved through various catalytic mechanisms including acid-base, covalent, and metal ion catalysis.
2) Michaelis-Menten kinetics describe enzyme-catalyzed reactions, relating reaction velocity to substrate concentration. The Michaelis constant Km and maximum velocity Vmax are important parameters.
3) Different kinetic approaches like rapid equilibrium and steady state are used to derive rate equations depending on if reaction steps are at equilibrium. Rate equations can be plotted and analyzed to determine
Catalysis is the process by which a catalyst speeds up a chemical reaction without being consumed. There are different types of catalysis including homogeneous, heterogeneous, positive, negative, and auto-catalysis. Catalysts lower the activation energy of reactions and remain unchanged after reactions. They can accelerate millions of reaction cycles. Characteristics of catalysts are that they are specific, used in small amounts, and do not change reaction equilibrium or thermodynamics.
Enzymes use several catalytic mechanisms to lower the free energy of transition states and greatly increase reaction rates, including acid-base catalysis, covalent catalysis, metal ion catalysis, and bringing substrates into close proximity and proper orientation. Acid-base catalysis involves proton transfer from catalytic amino acid side chains. Covalent catalysis transiently forms covalent bonds between enzyme and substrate. Metal ion catalysis uses transition metals to orient substrates, mediate redox reactions, or stabilize charges. Proximity and orientation align substrates for reaction, while catalysis by approximation brings two substrates together for reaction.
Catalysis and catalysts - Introduction and applicationManoj Mohapatra
1. Catalysts play an essential role in many life processes like photosynthesis and in maintaining the environment. They are also crucial in the chemical industry, contributing to 90% of chemical processes.
2. Catalysts participate in and alter the rates of chemical reactions while remaining unchanged themselves. They allow reactions to proceed under milder conditions with less energy.
3. The main requirements for a good catalyst are that it promotes the desired reaction rate selectively while also being stable and resistant to deactivation over time.
1. Catalysts play a key role in many life processes and industrial applications. They contribute greatly to photosynthesis and the conversion of sun energy into other forms of energy.
2. Catalysts increase reaction rates and allow reactions to proceed under milder conditions with less energy and raw material usage. This improves process efficiency and reduces waste.
3. Almost all chemical industries employ catalytic processes in one or more steps due to the economic and environmental benefits. Over 90% of chemical industry processes involve catalysis.
The document provides an overview of catalysis. It defines a catalyst as a substance that speeds up a chemical reaction but is not consumed by the reaction. It discusses different types of catalysis including homogeneous catalysis where the catalyst is in the same phase as the reactants, and heterogeneous catalysis where the catalyst is in a different phase. The document also covers catalyst characterization techniques, factors that can lead to catalyst deactivation, and methods for catalyst regeneration. Examples are provided throughout to illustrate catalysis concepts and applications.
It shows the basic facts of catalyst along with its importance in industry along with its long last milestone,its characteristics & application in industry its reaction process and preparation of a solid catalyst.
This document summarizes information about simple eutectic systems and enzyme catalysis. It first discusses the lead-silver eutectic system, noting that lead and silver are completely miscible in liquid state but immiscible in solid state, forming a simple eutectic system. The phase diagram shows the eutectic point occurs at 2.5% silver and 97.5% lead with a temperature of 327°C. It then discusses enzyme catalysis, noting enzymes are protein catalysts that increase reaction rates via an active site. The two main theories of catalysis are intermediate compound formation and adsorption, while the two main theories of enzyme catalysis are the lock-and-key and induced fit
Phase Transfer Catalysis and Ionic liquids Gopika M G
Mechanism of Phase Transfer Catalysis, Examples of Phase Transfer Catalysts, Catalysis by Ionic Liquids, Examples of Ionic Liquids, Reactions involving Ionic Liquids.
chemoselective oxidation of secondary alcohols using a ruthenium phenylendeny...VasiUddin Siddiqui
i make this presentation for my seminar project.basically it is a paper work done by Simone Manzini, César A. Urbina-Blanco, and Steven P. Nolan*EaStCHEM School of Chemistry, University of St Andrews, St Andrews, U.K. KY16 9ST ..
Catalysts accelerate chemical reactions while remaining unchanged. There are two types of catalyzed reactions: heterogeneous, where reactants and catalysts are in different phases, and homogeneous, where they are in the same phase. Catalysts lower activation energy and increase reaction rate without affecting products or equilibrium. They are often specific to certain reactions. Promoters increase catalytic activity while inhibitors decrease it. Poisons deactivate catalysts permanently or temporarily. Enzymes are biological catalysts that catalyze specific biochemical reactions optimally at 15-25°C. Acid and base catalysts donate or accept protons to facilitate reactions.
1. Homogeneous Catalysis
HMC-1- 2010
Dr. K.R.Krishnamurthy
National Centre for Catalysis Research
Indian Institute of Technology, Madras
Chennai-600036
2. Homogeneous Catalysis- 1
Basics
Homogeneous Catalysis- General features
Metal complex chemistry- Metals & Ligands –bonding & reactivity
Reaction cycles
Reaction types/ Elementary reaction steps
Kinetics & Mechanism
3. Catalysis
1850 Berzelius C a ta ly z e d r x n
p ro c e e d in g th r o u g h
1895 Ostwald: A catalyst is a a n in te r m e d ia te
substance that changes the rate of a
Ea
chemical reaction without itself
appearing into the products E a
∆G c a t a ly z e d
Definition: a catalyst is a substance
that increases the rate at which a R e a c ta n ts
∆G
chemical reaction approaches
equilibrium without becoming itself P ro d u c ts
permanently involved.
Catalysis is a kinetic phenomenon.
R e a c tio n C o o r d in a te
Catalysis –Types
Heterogeneous
Homogeneous
Enzymatic/Bio
Obeys laws of thermodynamics Photo/Electro/Photo-electro
Phase transfer
4. Homogeneous Catalysis
Reactions wherein the Catalyst components and substrates of the reaction
are in the same phase, most often the liquid phase
Mostly soluble organometallic complexes are used as catalysts
Characterized by high TON & TOF
Operate under milder process conditions
Amenable to complete spectroscopic characterization
Homogeneous processes without a heterogeneous counterpart:
Pd-catalyzed oxidation of ethylene to acetaldehyde (Wacker process)
Ni-catalyzed hydrocyanation of 1,3-butadiene to adiponitrile (DuPont)
Rh- and Ru-catalyzed reductive coupling of CO to ethylene glycol
Enantioselective hydrogenation, isomerization, and oxidation reactions.
5. Catalysis- Heterogeneous Vs Homogeneous
Aspect Heterogeneous Homogeneous
Activity Comparable Comparable
Reproducibility Difficulty in reproducibility Reproducible results
Selectivity Heterogeneous sites. Difficult to control Relatively higher selectivity, easy to
selectivity optimize, various types of selectivity
Reaction conditions Higher temp. & pressure, better thermal Lower temp. (<250ºC), Higher pressure,
stability lower thermal stability
Catalyst cost & High volume –low cost. Easy catalyst Low volume, high value. Recovery
recovery recovery difficult. Major drawback
Active sites, nature Not well- defined, heterogeneous, Molecular active sites, very well defined,
& accessibility but tunable, limited accessibility uniform, tunable & accessible
Diffusion limitations Susceptible, to be eliminated with proper Can be overcome easily by optimization
reaction conditions of stirring
Catalyst life Relatively longer, regeneration feasible Relatively shorter, regeneration may/may
not be feasible
Reaction kinetics Complex kinetics & mechanism, Difficult Reaction kinetics ,mechanism & catalytic
mechanism & to establish & understand unequivocally activity could be established &
catalytic activity at l, but days are not far-off understood with relative ease
molecular level
Susceptibility to Highly susceptible Relatively less susceptible. Sensitive to
poisons water & oxygen
Industrial Bulk/Commodity products manufacture Pharma, fine & specialty chemicals
Application ~ 85% manufacture, ~15%
10. Transition-metal catalysts- Features / Potential
Activity & Selectivity can be controlled in several ways:
Strength of metal-ligand bond can be varied
Variety of ligands can be incorporated into the coordination sphere
Specific ligand effects can be tuned- constituents
Variable oxidations states are feasible
Variation in coordination number can be possible
Tailor made catalyst systems are possible
11. Effect of ligands and valance states on the selectivity
in the nickel catalyzed reaction of butadiene
( )
n
( )n
( )
n
Scheme: 1,3-butadiene reactions on “Ni”
14. 12 Principles of green chemistry
1. Prevent waste
2. Increase atom economy
3. Use and generate no / less toxic chemicals
4. Minimize product toxicity during function
5. Use safe solvents and auxiliaries
6. Carry out processes with energy economy (ambient temperature and
pressure)
7. Use renewable feedstocks
8. Reduce derivatives and steps
9. Use catalytic instead of stoichiometric processes
10. Keep in mind product life time (degradation vs. biodegradation processes)
11. Perform real-time analysis for pollution prevention
12. Use safe chemistry for accident prevention
Amenable for adoption in homogeneous catalysis
19. Basics - Reactivity of metal complexes
A metal complex:
The catalytic activity is influenced by the characteristics of the central metal ions
and attached ligands.
Metal
The oxidation state and the electron count (EC) of the valence shell of the metal ion
are the critical parameters for activity. A fully ionic model is implicit.
Activity of a metal complex is governed by
Rule of effective atomic number (EAN) or the 18 e- rule
EC=18- Co-ordinative saturation Inactive
EC < 18- Co-ordinative unsaturation Activity
Easy displacement of weakly bound ligands;
e.g., Zr Complex, THF can be easily replaced by the substrate and solvent
molecules.
Influenced of bulkier ligands; Steric constraints- Easy ligand dissociation
NiL4 ↔ NiL3 + L
Many complexes have electron counts less that 16
20. Metal complexes-Electron counts for activity
Oxidation state Electron
Cl PPh3 count
Rh 1+ 16
Ph3P PPh3
H
PPh3
Ph3P Rh 1+ 18
PPh3
CO
+
CH3
Zr 4+ 16
O
-
OC CO 1- 18
Co
OC CO
21. Homogeneous Catalysis- Reaction cycle
The catalytically active species must
have a vacant coordination site (total
valence electrons = 16 or 14) to allow
the substrate to coordinate.
Noble metals (2nd and 3rd period of
groups 8-10) are privileged catalysts
(form 16 e species easily).
In general, the total electron count
alternates between 16 and 18.
Ancillary ligands insure stability and a
good stereoelectronic balance.
One of the catalytic steps in the
catalytic cycle is rate-determining.
22. Homogeneous Catalysis
Role of ‘vacant site’ and Co-ordination of the substrate
Catalyst provides sites for activation of reactant (s)
Through surface/site activation the activation barrier for reaction is reduced.
In homogeneous as well as heterogeneous catalysts such active sites are
normally referred to as vacant site/ co-ordinatively unsaturated site (cus).
Substrates on adsorption at cus get activated
In a typical homogeneous catalyst the active site is a cus in a metal
complex
In heterogeneous catalysis, similar cus exist
In homogeneous phase, metal complexes are fully saturated with ligand &
solvent molecules
There is a competition between the desired substrate and the other potential
ligands present in the solution for co-ordination with metal ion.
Nature of interaction/binding between Metal- ligand-substrate-solvent
governs overall activity & selectivity
These interactions/exchange takes place via different routes:
Substitution
Associative
Dissociative
23. Homogeneous Vs Heterogeneous
Functional similarities
Homogeneous Functions Heterogeneous
Dissociation Metal-ligand bond breaking Desorption
Association Metal-ligand bond formation Adsorption
Oxidative addition Fission of bond in substrate Dissoc. Adsorption
Reductive elimination Bond formation towards product Association
24. Wilkinson’s catalyst: Oxidative addition of H2
H2 adds to the catalyst before the olefin.
The last step of the catalytic cycle is irreversible. This is very useful
because a kinetic product ratio can be obtained. S-Solvent
25. Metal complexes
Metal complexes retain identity in solution
Have characteristic properties- XRD,IR,UV,ESR
Double salts exist as individual species
32. Ligand Effects
A. Electronic Effects
P as donor element: Alkyl (aryl) phosphines (PR3) and organo phosphites
Alkyl phosphines are strong bases, good σ-donor ligands
Organo phosphites are strong π-acceptors and form stable complexes with
electron rich transition metals.
Metal to P bonding resembles, metal to ethylene and metal to CO
Which orbitals of P are responsible for π back donation?
Antibonding σ* orbitals of P to carbon (phosphine) or to oxygen (phosphites)
P
O P
C C O
Strong back donation-low C-O stretch Weak back donation-high C-O stretch
The σ-basicity and π-acidity can be studied by looking at the stretching frequency
of the coordinated CO ligands in complexes, such as Ni L(CO) 3 or Cr L(CO)5
in which L is the P ligand.
1) Strong σ donor ligands → High electron density on the metal and hence a
substantial back donation to the CO ligands → Lower IR frequencies
Strong back donation and low C – O stretch
34. 2) Strong π acceptor ligands will compete with CO for the electron back donation
and C-O stretch frequency will remain high
Weak back donation → High C – O stretch
The IR frequencies represent a reliable yardstick for the electronic properties of a
series of P ligands toward a particular metal, M.
CrL(CO)5 or NiL(CO)3 as examples; L = P(t-Bu)3 as reference
The electronic parameter, χ (chi) for other ligands is simply defined as the
difference in the IR frequencies of the symmetric stretch of the two complexes
Ligand, PR3, R= χ (chi) IR Freq (A1) of NiL(CO)3 in cm-1
T-Bu 0 2056
N-Bu 4 2060
4-C6H4NMe3 5 2061
Ph 13 2069
4-C6H4F 16 2072
CH3O 20 2076
PhO 29 2085
CF3CH2O 39 2095
Cl 41 2097
(CF3)2CHO 54 2110
F 55 2111
CF3 59 2115
35. B. Steric Effects
1) Cone angle (Tolman’s parameter, θ) (Monodentate ligands)
From the metal center, located at a distance of
2.28 A from the phosphorus atom in the appropriate
direction, a cone is constructed with embraces all the
atoms of the substituents on the P atom, even though
ligands never form a perfect cone.
Sterically, more bulky ligands give less stable complexes
Cone angle
Crystal structure determination, angles smaller than θ M
P
values would suggest.
Thermochemistry: heat of formation of metal-phosphine adducts.
When electronic effects are small, the heats measured are a measure of the
steric hindrance in the complexes.
Heats of formation decrease with increasing steric bulk of the ligand.
Ligand, PR3; R = H θ value = 87
CH3O 107
n-Bu 132
PhO 128
Ph 145
i-Pr 160
C6H11 170
t-Bu 182
36. An ideal separation between Steric and electronic parameters is not possible.
Changing the angle will also change the electronic properties of the phosphine
ligand.
Both the χ- and θ- values should be used with some reservation
Predicting the properties of metal complexes and catalysts:
Quantitative use of steric and electronic parameters (QALE)
The use of χ- valaues in a quantitative manner in linear free energy relationships
(LFER)
Tolman’s equation:
Property = a + b(χ) + cθ
The property could be log of rate constant, equilibrium constant, etc.
Refinements:
Property = a + b (χ) + c(θ – θth)λ
where, λ, the switching factor, reads 0 below the threshold and 1 above it.
Refinement, the electronic parameter:
Property = a(χd) + b(θ – θth)λ + c(Ear) + d(πp) + e
where χd is used for σ-donicity and πp used for π-acceptor property;
Ear is for “aryl effect”.
For reactions having a simple rate equation, the evaluation of ligand effects with
the use of methods such as QALE will augment our insight in ligand effects,
a better comparison of related reactions, and a useful comparison between
different metals.
37. Bite angle effects (bidentate ligands)
Diphosphine ligands offer more control over regio- and stereoselectivity in many
catalytic reactions
The major dfiference between the mono- and bidentate ligands is the ligand
backbone, a scaffold which keeps the two P donor atoms at a specific distance.
This distance is ligand specific and it is an important characteristic, together with
the flexibility of the backbone
P
O P P
P P
P P X
P
X
X
Many examples show that the ligand bite angle is related to catalytic performance
in a number of reactions.
Pt-diphosphine catalysed hydroformylation
Pd catalyzed cross coupling reactions of Grignard reagents with organic halides
Rh catalyzed hydroformylation
Nickel catalyzed hydrocyanation and
Diels-Alder reactions
38. Ligands - Types & properties
1. Ligands: CO, R2C=CR1, PR3 and H- (N2, NO, etc.)
All ligands behave as Lewis bases and the M acts as a Lewis acid
Alkenes: π electrons
Whereas H2O and NH3 accept e- density from the metal, i.e., they act as
Lewis Acids (π acid ligands)
The donation of e- density by the metal atom to the ligand is referred to
as back donation.
H2 acts as a Lewis acid.
Also, Lewis acid-like behaviour of CO, C2H4 and H2 in terms of overlaps
between empty orbitals of the ligand and the filled metal orbitals of
compatible symmetry.
Back donation is a bonding interaction between the metal atom and
the ligands, because the signs of the donating metal ‘d’ orbitals and
the ligand π* (σ* for H2) acceptor orbitals match.
The π ligands play important roles in a large number of homogeneous
catalytic reactions.
39. Acids & Bases
Lewis acids
A Lewis acid accepts a pair of
electrons from other species
Bronsted acids transfer protons
while Lewis acids accept electrons
A Lewis base transfers a pair of
electrons to other species BF3- Lewis acid; Ammonia- Lewis base
40.
41. 2. Alkyl, Allyl and alkylidene ligands
Alkyl ligands: Two reactions M-Alkyl-Single bond- M-C
M-Alkylidene-Double bond M=C
a) Addition of RX to unsaturated metal center M-Allyl group
R
R
M + M
X X
Oxidation state: +n +n+2
valence electrons: p p-2
b) Insertion of alkene into a metal-H or an existing metal-C bond
R R
M M
H H H
H
Reactivity of metal-alkyls: kinetic instability towards conversion by β-hydride
elimination.
Others:
α-hydride elimination H
H H
M R
Agostic interaction M R H
Metallocycle formation
43. Homogeneous Catalysis –Key reaction steps
1. Ligand Coordination and Dissociation
2. Oxidative addition and Reductive elimination
3. Insertion and Elimination
4. Nucleophilic attack on coordinated ligands
5. Oxidation and Reduction
44. 1. Ligand Coordination and Dissociation
Basis
Easy coordination of substrate to the metal center-activation
Facile elimination of product from the metal coordination sphere- Desorption ?
Requirement
Co-ordinative unsaturation- active centre
Highly labile metal complex- activity
Substitution- addition-dissociation-migration
Examples E.g., Wilkinson’s catalyst
Many square-planar complexes with 16e
EC are highly active. Ph3P Cl
ML4 complexes of Pd(II), Pt(II) and Rh(I) Rh
are commonly used as catalysts. Ph3P PPh3
45. 2. Oxidative Addition & Reductive Elimination
Oxidative Addition
Addition of a molecule AX to a complex
Steps
Dissociation of the A—X bond
Coordination of the two fragments to the metal center
A
L L
L M L + AX L M X
L L
L
Reductive Elimination
Reverse of oxidative addition:
Steps
Formation of a A—X bond
Dissociation of the AX molecule from the coordination sphere
48. 3. Insertion and Elimination
Insertion : Migration of alkyl (R) or hydride (H) ligands from the metal center
to an unsaturated ligand
R L H
O
CH2
L + M C O M C R M M CH2CH3
CH2
Elimination:
Migration of alkyl (R) or hydride (H) ligands from a ligand to the metal center
e.g., β-hydride elimination
H CH2 H H
-C2H4
CH2
M CH2 CH3 M CH2 M M Sol
CH2 +Sol
49. 3. Insertion reactions : Migratory insertion - Examples
H
H
M M Insertion of olefin into M-H bond
R
R
M M Insertion of olefin into M-R bond
O
R
M Insertion of CO into M-R bond
CO M R
Migratory insertion of R in M-CO
O
H
M Insertion of CO into M-H bond
M H
CO
51. L H L
Insertion
Rh Rh
ß-elimination L
L
L = PPr3i
M +
M H n
H n
Polymer chain termination by ß-elimination
52. 4. Nucleophilic Attack on Coordinated Ligands
A (+)ve charge on a metal-ligand complex tends to activate the coordinated C
atom toward attack by a nucleophile.
H H 2+ +
OH2 H H
L C L
L Pd L Pd C C OH + H+
L C L H R
H R
53. Nucleophilic attack on a coordinated ligand
Upon coordination to a metal center, the electronic environment of the ligand
undergoes a change. The ligand may become susceptible to electrophilic or
nucleophilic attack.
OH
Pd
2+
+ H2O [ Pd ]+ + H+
R
O R
4+
+ Ti
4+
O + O
Ti O
H H
O -
Fe CO + HO- Fe
OH
The extent of the reactivity of the ligand is reflected in the rate constants
54. 5. Oxidation and Reduction
During a catalytic cycle, metal atoms frequently alternate between two oxidation
states:
Cu2+/Cu+ Co3+/Co2+ Mn3+/Mn2+ Pd2+/Pd
Catalytic Oxidation: generating alcohols and carboxylic acids
The metal atom 1) initiates the formation of the radical R•
2) contributes to the formation of R-O-O• radical
R H + Co(III) R + H + Co(II)
R + O2 R H
R O O R O O H + R
R O O H + Co(II) R O + Co(III)OH R O O H + Co(III) R O O + H + Co(II)
AND
55. The Catalytic Cycle –Elementary steps
Example: A metal complex catalyzed hydrogenation of an alkene
Alkene + H2 → Alkane
MLn+1 ⇋ MLn + L
MLn+ + H2 ⇋ H2MLn
H2MLn + alkene ⇋ H2MLn(alkene)
H2MLn(alkene) ⇋ HMLn(alkyl)
HMLn(alkyl) → MLn + alkane
56.
57. Kinetic studies
Reaction rates
Dependent on the concentration of reactants and the products in some
cases
Useful in understanding the mechanism of the reaction
Empirically derived rate expressions
Ligand dissociation
Leads to generation of catalytic active intermediate.
Addition of ligand in such a catalytic system, the rate of the reaction
decreases.
Examples
CO dissociation in Co-catalyzed hydroformylation
Phosphine dissociation in RhCl(PPh3) catalyzed hydrogenation
Cl- dissociation in the Wacker process
58. Michaelis-Menten Kinetics
(Enzyme catalysed reactions - Saturation kinetics
Rate = k.K[substrate][catalyst]/1 + K[substrate]
A complex is formed between the substrate and the catalyst by
a rapid equilibrium reaction.
K -The equilibrium constant of this reaction
k- rate constant for rate-determining step
Increasing the substrate concentration will increase the rate
initially, followed by more or less constant rate
At high substrate concentration, when
K[substrate] ~ 1 + K[substrate]
At constant catalyst concentration, plot of (1/rate) vs. (1/(substrate)
will give a straight line.
59. Homogeneous Catalysis- Kinetics & Mechanism
a. Kinetic studies and mechanistic insight
i) Macroscopic rate law
ii) Isotope labelling and its effect on the rate
or stoichiometry
iii) Rate determining step
iv) Variation of ligand structure and its
influence on ‘k’
b. Spectroscopic investigations
‘in-situ’ IR, NMR, ESR
c. Studies on model compounds
d. Theoretical calculations
60. Limitations:
- Kinetic studies are informative about the slowest step only,
not other steps.
- Spectroscopic investigations of a complex requires a
minimum concentration.
- It is possible that the catalytically active intermediates
never attain such concentrations and therefore,
not observed.
-The species that are seen by spectroscopy may not be
involved in the catalytic cycle!
However, a combination of kinetic and spectroscopic methods
can resolve such uncertainties to a large extent.
61. Reference Books
1. Homogeneous Catalysis: The Applications and Chemistry
of Catalysis by soluble Transition Metal Complexes,
G.W. Parshall and S.D. Ittel,
Wiley, New York, 1992.
2. Applied Homogeneous Catalysis with Organometallic
Compounds,
Vols 1 & 2, edited by B. Cornils and W.A. Herrmann, VCH,
Weinheim,New York, 1996.
3. Homogeneous Catalysis: Mechanisms and Industrial
Applications,
S. Bhaduri and D. Mukesh, Wiley, New York, 2000.
4. Homogeneous catalysis: Understanding the Art,
Piet W.N.M. van Leeuwen,
Kluwer Academic Publishers, 2003.
5. Catalysis-An integrated approach- R.A.van Santen, Piet W.N.M. van Leeuwen,
J.A.Moulijn &B.A.Averill