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Questions and Answers
What is the chemical process where a metal is inserted into a σ-bond, resulting in the formation of new metal-ligand bonds?
What is the chemical process where a metal is inserted into a σ-bond, resulting in the formation of new metal-ligand bonds?
Oxidative addition
What is the name given to the reverse process of oxidative addition?
What is the name given to the reverse process of oxidative addition?
Reductive elimination
Oxidative addition always results in a decrease in the coordination number of the metal.
Oxidative addition always results in a decrease in the coordination number of the metal.
False (B)
Both polar and non-polar σ-bonds can undergo oxidative addition
Both polar and non-polar σ-bonds can undergo oxidative addition
What two chemical reactions contribute to the formation of a Grignard reagent?
What two chemical reactions contribute to the formation of a Grignard reagent?
What is the general rule for the electron count of transition metal complexes that undergo oxidative addition?
What is the general rule for the electron count of transition metal complexes that undergo oxidative addition?
Oxidative addition can only occur intermolecularly.
Oxidative addition can only occur intermolecularly.
Alkylation and protonation reactions always lead to a change in the total electron count of the metal complex.
Alkylation and protonation reactions always lead to a change in the total electron count of the metal complex.
What is the name of the 16-electron square planar iridium complex that was instrumental in the early understanding of oxidative addition?
What is the name of the 16-electron square planar iridium complex that was instrumental in the early understanding of oxidative addition?
Which of the following are general pathways for oxidative addition? (Select all that apply)
Which of the following are general pathways for oxidative addition? (Select all that apply)
In general, which type of σ-bond is more likely to undergo concerted oxidative addition?
In general, which type of σ-bond is more likely to undergo concerted oxidative addition?
What type of transition state is involved in concerted oxidative addition reactions?
What type of transition state is involved in concerted oxidative addition reactions?
Concerted oxidative addition involves the retention of configuration at both reacting atoms.
Concerted oxidative addition involves the retention of configuration at both reacting atoms.
What is the name of the complex that forms prior to the actual oxidative addition in concerted oxidative addition?
What is the name of the complex that forms prior to the actual oxidative addition in concerted oxidative addition?
The oxidative addition of H2 to a metal complex is an example of a concerted reaction.
The oxidative addition of H2 to a metal complex is an example of a concerted reaction.
What is the name of the complex formed when H2 interacts with a metal complex?
What is the name of the complex formed when H2 interacts with a metal complex?
What interaction weakens the σ-bond in a dihydrogen complex?
What interaction weakens the σ-bond in a dihydrogen complex?
Oxidative addition of H2 can occur even in cases where the metal is not very basic.
Oxidative addition of H2 can occur even in cases where the metal is not very basic.
What specific type of oxidative addition reaction is the formation of a dihydride complex from H2 considered to be?
What specific type of oxidative addition reaction is the formation of a dihydride complex from H2 considered to be?
The oxidative addition of H2 results in the metal being reduced by two electrons.
The oxidative addition of H2 results in the metal being reduced by two electrons.
The example of oxidative addition with dihydrogen can be generalized to any σ-bond.
The example of oxidative addition with dihydrogen can be generalized to any σ-bond.
Oxidative addition generally begins with coordination of the σ-bond to the metal center.
Oxidative addition generally begins with coordination of the σ-bond to the metal center.
Oxidative addition of H2 is less facile than oxidative addition of a C-H bond.
Oxidative addition of H2 is less facile than oxidative addition of a C-H bond.
What are the primary factors that influence the ease of oxidative addition reactions?
What are the primary factors that influence the ease of oxidative addition reactions?
What type of metal complex is often involved in concerted oxidative addition reactions with aryl halides?
What type of metal complex is often involved in concerted oxidative addition reactions with aryl halides?
Pd(0) complexes readily undergo oxidative addition with aryl halides even if they have 18 electrons.
Pd(0) complexes readily undergo oxidative addition with aryl halides even if they have 18 electrons.
What is the type of oxidative addition where a nucleophilic metal center attacks a σ-bond by an SN2 mechanism?
What is the type of oxidative addition where a nucleophilic metal center attacks a σ-bond by an SN2 mechanism?
The SN2 pathway for oxidative addition involves the retention of configuration at the electrophile.
The SN2 pathway for oxidative addition involves the retention of configuration at the electrophile.
Alkylation reactions of nucleophilic metal complexes typically proceed via the SN2 mechanism.
Alkylation reactions of nucleophilic metal complexes typically proceed via the SN2 mechanism.
Oxidative addition by the SN2 mechanism is accelerated in non-polar solvents.
Oxidative addition by the SN2 mechanism is accelerated in non-polar solvents.
Both concerted and SN2 mechanisms involve a two-electron process for oxidative addition.
Both concerted and SN2 mechanisms involve a two-electron process for oxidative addition.
What is the other pathway for oxidative addition, besides the concerted and SN2 mechanisms?
What is the other pathway for oxidative addition, besides the concerted and SN2 mechanisms?
The products formed via single electron transfer mechanisms are always different from the products formed via a concerted mechanism.
The products formed via single electron transfer mechanisms are always different from the products formed via a concerted mechanism.
Single electron transfer mechanisms are only observed with first-row transition metals.
Single electron transfer mechanisms are only observed with first-row transition metals.
What type of experimental technique can be used to determine if a reaction proceeds through a radical mechanism?
What type of experimental technique can be used to determine if a reaction proceeds through a radical mechanism?
Single electron transfer pathways are generally inefficient in oxidative addition reactions.
Single electron transfer pathways are generally inefficient in oxidative addition reactions.
Metal complexes with an odd number of d electrons are not good candidates for radical oxidative addition.
Metal complexes with an odd number of d electrons are not good candidates for radical oxidative addition.
Manganese undergoes a two-electron change in oxidation state during the reaction of a binuclear manganese carbonyl complex with bromine.
Manganese undergoes a two-electron change in oxidation state during the reaction of a binuclear manganese carbonyl complex with bromine.
The same metal complex can exhibit different mechanisms of oxidative addition depending on the activated bond.
The same metal complex can exhibit different mechanisms of oxidative addition depending on the activated bond.
What is the reverse process of oxidative addition, where a metal center returns to a lower oxidation state by eliminating two ligands?
What is the reverse process of oxidative addition, where a metal center returns to a lower oxidation state by eliminating two ligands?
Reductive elimination is not affected by the factors that influence the rate of oxidative addition.
Reductive elimination is not affected by the factors that influence the rate of oxidative addition.
Oxidative addition and reductive elimination are always irreversible processes.
Oxidative addition and reductive elimination are always irreversible processes.
The reductive elimination process always results in the formation of a sigma complex.
The reductive elimination process always results in the formation of a sigma complex.
Reductive elimination always results in a decrease in the coordination number of the metal center.
Reductive elimination always results in a decrease in the coordination number of the metal center.
The mechanisms for reductive elimination are distinct from those for oxidative addition.
The mechanisms for reductive elimination are distinct from those for oxidative addition.
Reductive elimination is always faster for electron-rich metal complexes.
Reductive elimination is always faster for electron-rich metal complexes.
First-row transition metals tend to undergo reductive elimination at a slower rate than second or third-row metals.
First-row transition metals tend to undergo reductive elimination at a slower rate than second or third-row metals.
Ligand dissociation is a necessary step in reductive elimination for square planar complexes.
Ligand dissociation is a necessary step in reductive elimination for square planar complexes.
Steric hindrance around the metal center generally slows down reductive elimination.
Steric hindrance around the metal center generally slows down reductive elimination.
For concerted reductive elimination, the ligands undergoing elimination must be in a trans configuration.
For concerted reductive elimination, the ligands undergoing elimination must be in a trans configuration.
C-H reductive elimination is typically more facile than C-C reductive elimination.
C-H reductive elimination is typically more facile than C-C reductive elimination.
Reductive elimination involving sp³-hybridized carbons is often faster than that involving sp²-hybridized carbons.
Reductive elimination involving sp³-hybridized carbons is often faster than that involving sp²-hybridized carbons.
The role of supporting ligands like phosphines in reductive elimination is minimal.
The role of supporting ligands like phosphines in reductive elimination is minimal.
Bulkier, less electron-rich phosphines typically slow down reductive elimination.
Bulkier, less electron-rich phosphines typically slow down reductive elimination.
Flashcards
Oxidative Addition
Oxidative Addition
A reaction where a metal inserts into a σ-bond, increasing the metal's oxidation state and coordination number, and formally adding two electrons.
Reductive Elimination
Reductive Elimination
The reverse of oxidative addition, where a metal loses a ligand and decreases its oxidation state and coordination number, and formally removing two electrons.
σ-bond
σ-bond
A single covalent bond formed from direct overlap of electron density on two orbitals along the bond axis.
Oxidation State (Mn+)
Oxidation State (Mn+)
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Coordination Number
Coordination Number
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Electron Count (dn)
Electron Count (dn)
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Concerted Oxidative Addition
Concerted Oxidative Addition
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SN2 Mechanism
SN2 Mechanism
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Single Electron Processes
Single Electron Processes
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Grignard Reagent
Grignard Reagent
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Cyclometallation
Cyclometallation
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Vaska's Compound
Vaska's Compound
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Aryl Halide
Aryl Halide
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Alkylation
Alkylation
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Protonation
Protonation
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H2 Oxidative Addition
H2 Oxidative Addition
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Radical Mechanisms
Radical Mechanisms
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cis
cis
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trans
trans
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Orbital Interactions
Orbital Interactions
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Electron-poor complex
Electron-poor complex
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Reductive Elimination
Reductive Elimination
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Concerted Reductive Elimination
Concerted Reductive Elimination
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Study Notes
Oxidative Addition
- Oxidative addition involves the insertion of a metal into a σ-bond, increasing the oxidation state of the metal by two electrons.
- Both polar and non-polar σ-bonds can participate in this reaction.
- The reaction is reversible. The reverse reaction is reductive elimination.
Reductive Elimination
- Reductive elimination is the reverse of oxidative addition.
- The reaction proceeds with a reduction of the oxidation state of the metal by two electrons.
- Oxidative addition and reductive elimination are frequently reversible, with thermodynamics dictating the directionality.
Mechanisms for Oxidative Addition
- There are three general pathways for oxidative addition: concerted, SN2, and single electron transfer.
- Concerted pathways typically involve a three-membered transition state, resulting in a cis product. The mechanism occurs via prior formation of a sigma complex.
- SN2 mechanisms are analogous to organic SN2 reactions, involving inversion of configuration at the electrophile.
- Single electron transfer mechanisms commonly involve radical and outer sphere electron transfer processes
- The choice of pathway often depends on the nature of the bond being activated and the specific metal center.
Mechanisms for Reductive Elimination
- The pathways for reductive eliminations mirror those of oxidative addition.
- Concerted mechanisms involve cis elimination of the ligands.
- Reductive elimination with C-H bonds is generally favored over C-C bonds.
- Steric hindrance plays a role in determining the rate of reductive elimination.
- Reductive elimination rates are typically faster when the transition metal center is electron-poor. Typically first-row transition metals exhibit faster reductive elimination reactions compared to 2nd and 3rd row ones.
- Ligand dissociation may be necessary (i.e. a ligand is lost) prior to reductive elimination.
Example Reactions
- Oxidative addition of H2, involves tungsten (W). In this, the W atom is oxidized by two electrons, and the H-H bond is broken to form W-H bonds.
- Oxidative addition of aryl halides, Pd(0) complexes may exhibit oxidative addition of aryl halides. During this process, a phosphine ligand (or other ligand) may dissociate prior to the oxidative addition step.
- Alkylation/protonation of metals: These reactions typically include formal oxidative addition, where the metal is oxidized but the conjugate base is not bonded to the metal. Hence no change in electron count occurs.
- Reaction of Vaska's compound with CH3I, demonstrating nucleophilic attack by a metal complex.
Orbital Considerations
- Interactions in oxidative addition reactions, often utilizing dihydrogen complexes as examples, are often involved in the formation of σ complexes.
- Stabilizing effects often involve donation of electrons in the σ bonding orbital of the bond to be added to the metal (and possibly donation of electrons from the metal's d orbital to the σ* orbital of the bond to be added).
Other σ-bonds
- The reactivity shown in dihydrogen complex reactions (and other σ bonds) can be generalized to other σ-bonds.
- The metal center undergoing oxidative addition is usually oxidized by two electrons, and the total electron count is increased by two.
- The mechanism often involves initial coordination of the σ-bond to the metal center.
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Description
This quiz explores the concepts of oxidative addition and reductive elimination in coordination chemistry. It delves into the mechanisms involved, the nature of σ-bond participations, and the thermodynamic aspects that govern these reversible reactions. Test your understanding of these fundamental processes and their significance in metal-catalyzed reactions.
