Chemistry of Metal Complexes

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Questions and Answers

What happens to the oxidation state and coordination number of the metal in this process?

They both increase

They remain unchanged (correct)

They both decrease

They are not affected by the process

How many mechanisms are involved in this process?

One

Two (correct)

Three

Four

What is the rate-determining step in the dissociative mechanism?

The fast step

The last step

The slow step (correct)

The first step

What type of liaisons are involved in the concerted mechanism with 3 centers?

Apolare or slightly polar liaisons Signup and view all the answers

What is similar to the dissociative mechanism in organic chemistry?

SN1 Signup and view all the answers

What is the geometry of the product formed in the concerted mechanism?

Cis Signup and view all the answers

What is the formula of the metal complex at the beginning of the process?

R3PNi(CO)3 Signup and view all the answers

What happens to the number of electrons during the reaction?

It decreases by two units Signup and view all the answers

What is the product of the process?

Ni(CO)4 Signup and view all the answers

What type of addition is necessary for the resulting intermediate to stabilize?

Non-oxidative addition Signup and view all the answers

How many types of mechanisms regulate the synthesis of Grignard reagents?

4 Signup and view all the answers

What happens to the coordination number of the metal in the dissociative mechanism?

It decreases Signup and view all the answers

Which of the following can be coupled together?

All of the above Signup and view all the answers

Which of the following mechanisms is analogous to the mechanism in organic chemistry?

SN2 mechanism Signup and view all the answers

What is a characteristic of metals that makes oxydative coupling easier?

Basicity (rich in electrons) Signup and view all the answers

What is the role of L in the dissociative mechanism?

It is a ligand Signup and view all the answers

What is the general formula of the reactants in the synthesis of Grignard reagents?

R-X + Mg Signup and view all the answers

What is the product of the synthesis of Grignard reagents?

RMgX Signup and view all the answers

What is the general trend in the reactivity of alcynes versus alkenes?

Alcynes are more reactive than alkenes Signup and view all the answers

What is the role of the metal complex in the reaction?

It acts as a catalyst Signup and view all the answers

What is the result of the elimination of a ligand L in a complex?

The number of electrons in the complex decreases by 2 units. Signup and view all the answers

What is the general purpose of the II-3 elimination reaction?

To permit the substitution of ligands L or to allow for oxidative addition. Signup and view all the answers

What type of reaction is represented by the equation HCo(CO)4 → HCo(CO)3 + CO?

II-3 elimination reaction Signup and view all the answers

What is the maximum number of electrons in the complex LnM in an oxidative addition reaction?

16 Signup and view all the answers

What is the oxidation state of the metal in the complex Ni(CO)3?

0 Signup and view all the answers

What type of ligands are involved in an oxidative addition reaction?

Ligands with 1 electron Signup and view all the answers

What is the result of the reaction Pt(PPh3)3 + PPh3 → Pt(PPh3)4?

The addition of a ligand L Signup and view all the answers

What is the general equation for the II-3 elimination reaction?

MXL4 → MXL3 + L Signup and view all the answers

What is the advantage of using rhodium complexes over palladium complexes?

They offer better regioselectivity Signup and view all the answers

What is the outcome of the elimination reaction (4) in the scheme?

Formation of an alkane Signup and view all the answers

What is the role of the metal (Rh) in the scheme?

To catalyze the hydrogenation reaction Signup and view all the answers

What is the reactant that undergoes hydrogenation in the scheme?

Alkene Signup and view all the answers

What is the catalyst used in the hydrogenation reaction?

Rhodium Signup and view all the answers

What is the net result of the reaction sequence?

Reduction of the alkene Signup and view all the answers

What is the significance of the scheme?

It demonstrates the application of catalytic synthesis Signup and view all the answers

Who is the author associated with the hydrogenation mechanism?

Halpern Signup and view all the answers

Study Notes

Organometallic Reactions

The degrees of oxidation and coordination of the metal, as well as the number of valence electrons, remain unchanged during the process.
The process occurs according to two limiting mechanisms: dissociative and associative.

Dissociative Mechanism

Resembles the SN1 mechanism in organic chemistry.
Example: Ni(CO)4 → Ni(CO)3 + CO
Rate-determining step: slow, followed by a rapid step.

Elimination Non-Reductive

Generally, the non-oxidative addition (Lewis base) is equilibrated in solution with the reverse reaction, which involves the dissociation of the M-L bond, i.e., the elimination of a ligand L.
Example: HCo(CO)4 → HCo(CO)3 + CO
The reaction releases a coordination site, and the number of electrons in the complex decreases by 2 units.

Oxidative Addition

Corresponds to the scheme: LnM + A → B → LnM
Involves the addition of an electron-deficient ligand A, resulting in the formation of a 3-coordinate intermediate.
Four types of mechanisms govern this type of reaction:
- Concerted 3-center mechanism
- SN2-like substitution mechanism
- Radical mechanism
- Ionic mechanism

Concerted 3-Center Mechanism

Involves apolar or weakly polar bonds (H-H, O-O, H-Si, H-C, etc.)
The product forms with a cis geometry, and the number of electrons decreases by 2 units, resulting in an unstable, non-isolable intermediate.
A subsequent non-oxidative addition is necessary to stabilize the product.

Catalytic Applications

Alkynes couple more easily than alkenes, and the coupling is facilitated by the basicity (electron richness) of the metal.
It is possible to couple two carbene molecules or a carbene and an olefin.
The alkane is obtained through reductive elimination (4) after insertion (3).
The Halpern mechanism (1977) illustrates the catalytic cycle of olefin hydrogenation.

Catalysis with Palladium

Rhodium complexes offer better regioselectivity than palladium complexes.

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Description

This quiz covers the process of metal complex formation and dissociation, including the dissociative and associative mechanisms. It involves the coordination and oxidation states of metal ions.