Reaction Cycles Flashcards by Megan Law

Name some charged ligands

X-, H-, CH3-, OH-, NR2-

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How to find d electron count

Group number - oxidation state

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How to know if a complex is low spin

Metal is 2nd/3rd row
Strong field ligands
High metal charge

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Octahedral splitting is high (tetrahedral is …)

Tetrahedral splitting is low = square planar

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How to know if complex is high spin

Metal is 1st row
Weak field ligands
Low metal charge

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Octahedral splitting is low (tetrahedral is …)

Tetrahedral is high = tetrahedral

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Counting electrons structure (NEUTRAL)

dn metal = n electrons
Total ligands electrons
Overall complex charge: + = -1e, - = +1e

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vacant site H
| |
M——(H) —> M=—

B-Hydride elimination:
Cis vacant site
Planar space for alkene
Stable alkene

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CO O=CMe O=CMe
/ / /
M —> M —> M
\ \ \
Me Vacant site R

Migratory Insertion:
Bulky ligands increase rate
More positive carbon increase rate
Eth or Meth are best at migrating

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A
/
M —> M + A—B
\
B

Reductive elimination:
Oxidation state= -2
d electrons= +2
Coordinatively saturated
Electron withdrawing groups on metal

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A
/
M + A—B ——> M
\
B

Oxidative addition:
Oxidation state =+2
d electrons =-2
Neutral molecule added
Coordinately unsaturated complex
EDG ligands

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Pre catalyst —> active catalyst

Thermal or photolysis ligand dissociation

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How to selectively increase the rate

Donor solvent for migratory insertion
Less substituted alkene
Conjugated alkene
Increase temperature

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Define Productivity

Grams made per mole of catalyst per unit of time

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Define Turn over number

Number of cycles catalyst completes in a set time
Nproduct / Ncatalyst = TON

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Define Turn over frequency

Moles of product by moles of catalyst over time

TON / time = TOF

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Why is selectivity the most important for a catalyst

Industrial processes are continuous, side products are a loss so a low yield can be fixed by recycling the starting material, increasing the catalyst loading and increasing the time for the reaction. Side products cannot be fixed.

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Methanol carbonylation

Methanol + CO —> methanonic acid

Draw the catalytic cycle for methanol carbonylation.

Organic cycle :
Methanol to methyl-iodide
Methylcarbonyl-iodide to methanoic acid
Organometallic cycle
Oxidative addition
Migratory insertion of CO
Reductive elimination

Rds for methanol carbonylation

Oxidative addition: Rh
Migratory insertion: Ir

Hydroformulation

Alkene to aldehyde

Draw the catalytic cycle for hydroformylation

Activation to 16e
Alkene insertion
1,2 migratory insertion of H
Ligand coordination
Migratory insertion of CO
Oxidative addition of H2
B-hydride elimination

What is the rds for hydroformylation

Oxidative addititon

Cross coupling reactions (Suzuki)

Aromatic-X + R-B(OH)2 —> Aromatic-R

Draw the catalytic cycle for Suzuki cross coupling reaction

Activation to 16e Oxidative addition Transmetalation Reductive elimination

Cross coupling reactions (Heck - alkene/arom)

R-Alkene + Aromatic-X —> R-Alkene-Aromatic Basic conditions

Cross coupling reactions (Heck - Alkene/Alkene)

R-Alkene + Alkene-X —> R-Conjugated Alkene

Draw the catalytic cycle for Heck Reaction mechanism

Activate catalyst to 14e Oxidative addition of Aromatic-X Ligand substitution for alkene 2,1 migratory insertion B-hydride elimination Ligand substitution of product Reductive elimination of HX

Cross coupling reaction (Amination)

Aromatic-X + NHR2 —> Aromatic-NR2 Strong base

Draw the catalytic cycle for Amination

Catalyst activation 16e Oxidative addition of Aromatic-X Ligand substitution of H for NHR2 Deprotination of NHR2 Reductive elimination of Aromatic-NR2

What is a cationic catalyst cycle

Alkene coordination THEN Oxidative Addition Chelating phosphene ligand Weakly coordinating ligand Overall positive charge on the complex

How to make chiral alkane

Prochiral alkene Stereoisomer phosphene ligands, one side bulky other side less bulky After reaction two stereoisomers made depending on what face of prochiral alkene is attacked

How to control stereoselectivity

Phosphene ligands have different sized substituents that cannot interconvert Phosphene ligands have the same sized substituents that cannot interconvert due to chiral backbone that sets the conformation The diastereoisomers that are formed are of different energies and stabilises

What is the main complication with controlling the stereoselectivity of catalysis

The most stable diastereoisomer doesn’t always lead to the major product, eg the rate of addition may be faster than that of the stable product so it progresses to form the product and the stable one doesn’t.

What are the different types of chiral ligands

Chiral backbone P-chiral (chelating phosphene ligands substituents are chiral) Chiral substituents Planar chirality Atropisomer

How do you control regioselectivity for a branches isomer in hydroformylation

Electron withdrawing R groups on the substituent

What is cooperative catalysis

One catalyst and one catalytic cycle but substrate activation happens across two sites

How does hydrogenation work in cooperative catalysis

The catalyst has 2 active sites the metal and a ligand with lone pair H2 binds and is split Metal H: Hydride Lone pair H: Proton The different reactivities bind ti the carbonyl group and control the reaction geometry

Asymmetric hydrogenation using different metals

Fe, needs CO ligand to make more Fe+ character Ru, for amides Rh is el clasico

Methoxy carbonylation

= + CO + MeOH —> MeCH2C(O)OMe + H2O + O=CH2 —> CH2C(=)C(O)OMe 100% atom efficiency and cheap

What’s the catalytic mechanism for methoxycarbonylation

Oxidative addition of = to form alkane Oxidative addition of CO to form carbonyl Reductive elimination with MeOH to form product and hydrated catalyst

What is the structure of the catalyst in the second step of methoxycarbonylation (polymerisation)

Pd catalyst with chelating phosphenes H+X-

Polymerisation mechanism of methoxycarbonylation

Rate of = and CO insertion (looped reaction for polymerisation) faster than termination step (reductive elimination)

How do you increase the selectivity for methoxycarbonylation (mechanism)

Pd with bulky t-butyl substituents keep selectivity to methyl propanoate But has poor stability = insertion CO insertion MeOH coordination and elimination of products (methanolysis)