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Homogeneous Catalysis > Reaction Cycles > Flashcards

Reaction Cycles Flashcards

1
Q

Name some charged ligands

A

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

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2
Q

How to find d electron count

A

Group number - oxidation state

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3
Q

How to know if a complex is low spin

A

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

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4
Q

Octahedral splitting is high (tetrahedral is …)

A

Tetrahedral splitting is low = square planar

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5
Q

How to know if complex is high spin

A

Metal is 1st row
Weak field ligands
Low metal charge

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6
Q

Octahedral splitting is low (tetrahedral is …)

A

Tetrahedral is high = tetrahedral

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7
Q

Counting electrons structure (NEUTRAL)

A

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

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8
Q

vacant site H
| |
M——(H) —> M=—

A

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

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9
Q

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

A

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

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10
Q

A
/
M —> M + A—B
\
B

A

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

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11
Q

A
/
M + A—B ——> M
\
B

A

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

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12
Q

Pre catalyst —> active catalyst

A

Thermal or photolysis ligand dissociation

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13
Q

How to selectively increase the rate

A

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

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14
Q

Define Productivity

A

Grams made per mole of catalyst per unit of time

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15
Q

Define Turn over number

A

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

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16
Q

Define Turn over frequency

A

Moles of product by moles of catalyst over time

TON / time = TOF

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17
Q

Why is selectivity the most important for a catalyst

A

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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18
Q

Methanol carbonylation

A

Methanol + CO —> methanonic acid

19
Q

Draw the catalytic cycle for methanol carbonylation.

A

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

20
Q

Rds for methanol carbonylation

A

Oxidative addition: Rh
Migratory insertion: Ir

21
Q

Hydroformulation

A

Alkene to aldehyde

22
Q

Draw the catalytic cycle for hydroformylation

A

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

23
Q

What is the rds for hydroformylation

A

Oxidative addititon

24
Q

Cross coupling reactions (Suzuki)

A

Aromatic-X + R-B(OH)2 —> Aromatic-R

25
Q

Draw the catalytic cycle for Suzuki cross coupling reaction

A

Activation to 16e
Oxidative addition
Transmetalation
Reductive elimination

26
Q

Cross coupling reactions (Heck - alkene/arom)

A

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

27
Q

Cross coupling reactions (Heck - Alkene/Alkene)

A

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

28
Q

Draw the catalytic cycle for Heck Reaction mechanism

A

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

29
Q

Cross coupling reaction (Amination)

A

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

30
Q

Draw the catalytic cycle for Amination

A

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

31
Q

What is a cationic catalyst cycle

A

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

32
Q

How to make chiral alkane

A

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

33
Q

How to control stereoselectivity

A

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

34
Q

What is the main complication with controlling the stereoselectivity of catalysis

A

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.

35
Q

What are the different types of chiral ligands

A

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

36
Q

How do you control regioselectivity for a branches isomer in hydroformylation

A

Electron withdrawing R groups on the substituent

37
Q

What is cooperative catalysis

A

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

38
Q

How does hydrogenation work in cooperative catalysis

A

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

39
Q

Asymmetric hydrogenation using different metals

A

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

40
Q

Methoxy carbonylation

A

= + CO + MeOH —> MeCH2C(O)OMe + H2O + O=CH2 —> CH2C(=)C(O)OMe

100% atom efficiency and cheap

41
Q

What’s the catalytic mechanism for methoxycarbonylation

A

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

42
Q

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

A

Pd catalyst with chelating phosphenes
H+X-

43
Q

Polymerisation mechanism of methoxycarbonylation

A

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

44
Q

How do you increase the selectivity for methoxycarbonylation (mechanism)

A

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)

Homogeneous Catalysis (2 decks)

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