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Coordinatinon chemistry:reaction of complexes - ligand substitution reactions

22 important questions on Coordinatinon chemistry:reaction of complexes - ligand substitution reactions

Are small metal ions labile or inert?

Very small metal ions are often less labile --> Greater ML strength , streakily difficult to approach for incoming ligands

What are other factors playing a role in ligand substitution?

Nature of incoming ligand and spectator ligand: Ligand already present on the complex that influence the substitution reaction

LIgand substitution constant

Kf=prod/reactant

How does the addition of multiple ligands go, and what does this do with the k value?

M+L --> ML kf1=[ML]/[M]*[L]
ML + L --> ML2 Kf2= [ML2]/[ML][L]
The more ligands are added --> the weaker kf value becomes --> more difficult to attach the ligand

What is known as the chelating effect?

Ligand can bind to two or more sites of a metal centre

What is the difference of ionic and covalent counting and count both for the following complex: [Fe(3+(CO)3Cll3

Difference: Ionic counting takes the charge into account of the metal centre and x-ligands contributes to 2e-. Covalent and ionic counting should be the same electron count!!!
Ionic: Fe3+ --> 8-3= 5 + CO=6 + Cl= 6 --> 17 e-
Covalent: Fe--> 8 + CO=6 Cl=3 --> 17e-

What can a higher k value indicate?

If the k value is higher --> this would indicate a more favourable complex formation --> think about chelate effect (could be due to this)

What is a cone angle?

Solid angle at meta M-P which encloses the van der waals surface of all ligand atoms or substituents over all rotational orientations

What does a increase in cone angle result in?

makes the bonds stronger --> makes it easier to lose the leaving group --> dissociative activation

What is the inner sphere redox reaction?

Bridge formation occurs followed by the electron transfer from one complex to the other

What is the outer sphere redox reaction?

No bridging ligand if formed between the reacting species. Electron is transferred from one species to the other

What is a reduction reaction

2H+ + 2e- --> H2
Opnemen van e-

H+ is the oxidator in a reduction reaction

What is an oxidation reaction?

Zn (s) --> Zn 2+ + 2e-
afstaan van e-
Zn(s) is the reductor in the oxidation reaction

Substrates that can perform oxidative addition to metal centers are non-electrophilic substrates, electrophilic substrates and substrates containing multiple bonds. Explain the non-electrophilic substrates and name examples.

Do not contain electronegative atoms and require an empty orbital on the metal centre --> pre-coordination. Examples: H2, C-H, Si-H, B-H N-H, S-S, C-C. Activate for oxidative addition by an occupied/non-bonding orbital: Pt(0)(PR3)2 + H2 --> Pt(2+)(PR3)2H2

Substrates containing multiple bonds

May or may not contain electroneg bonds but do need to have a double or triple bond. Only 1 pi bond is broken, leaving the sigma bond intact. Metal centre needed with an empty orbital that can pre-coordinate the nucleophilic ligand before the oxidative addition occurs.

What metal is the most reactive for oxidative addition?

Metal complex with:
- Most and strongest donor ligands
- Fewest pi-acceptors ligands
Most negative charge on metal

Reductive elimination, what are the general features?

Electron-poor metals favour reductive elimination
--> There is more plus charge --> More you will pull the ligand --> favours reductive elimination.

What are the three substitution mechanisms and explain all three.

-Assosiative mechanism: X-MLn --> X-MLn-Y --> X + MLn-Y --> Often observed for square planars.
-Dissociative mechanicsm: Intermediate with lower coordination number, first X leaves, then Y attaches --> X-MLn --> X+ MLn --> X+ MLn-Y (WCO(6)--> W(CO)5+CO --> WCO5(PPH3) (Two step)
-Interchange mechanism: X-ML--> X--MLn--y --> X+ Y-MLn (Occurs for many 6-coordinate species, no detectable intermediate)

Which mechanisms are detectable and which are not?

Detectable: Associative-dissociative act , Dissociative associative act
Not detectable : Associative-associative act , Dissociative dissociative act

What is associative activation?

Ex: P + CL(dien)+ + I- --> [PtI(dien)+ +Cl- Rate depends strongly on incoming ligand Y, in transition state significant bonding of the incoming ligand

What is dissociative activation?

Ex: [Ni(OH2)6]2+ + NH3 --> [Ni(NH3)(OH2)5]2+ +H2O. Formation of transition state mainly depending on the rate of the breaking bond of the leaving ligand.

How can you know if it is an associative or dissociative mechanism?

Delta V > 0 --> Volume TS > Volume initial state --> Dissociative
Delta V < 0 --> Volume TS < Volume initial state --> Associative
Delta S > 0 --> More disorder --> Dissociative
Delta S< 0 --> less disorder --> Associative

If k1 dominates (straight line) : horizontal --> Dissociative
If k2 dominates --> associative

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Inorganic Chemistry | 9780199641826

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Coordinatinon chemistry:reaction of complexes - ligand substitution reactions

22 important questions on Coordinatinon chemistry:reaction of complexes - ligand substitution reactions

Are small metal ions labile or inert?

What are other factors playing a role in ligand substitution?

LIgand substitution constant

How does the addition of multiple ligands go, and what does this do with the k value?

What is known as the chelating effect?

What is the difference of ionic and covalent counting and count both for the following complex: [Fe(3+(CO)3Cll3

What can a higher k value indicate?

What is a cone angle?

What does a increase in cone angle result in?

What is the inner sphere redox reaction?

What is the outer sphere redox reaction?

What is a reduction reaction

What is an oxidation reaction?

Substrates that can perform oxidative addition to metal centers are non-electrophilic substrates, electrophilic substrates and substrates containing multiple bonds. Explain the non-electrophilic substrates and name examples.

Substrates containing multiple bonds

What metal is the most reactive for oxidative addition?

Reductive elimination, what are the general features?

What are the three substitution mechanisms and explain all three.

Which mechanisms are detectable and which are not?

What is associative activation?

What is dissociative activation?

How can you know if it is an associative or dissociative mechanism?

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