Reaction Cycles Flashcards
Name some charged ligands
X-, H-, CH3-, OH-, NR2-
How to find d electron count
Group number - oxidation state
How to know if a complex is low spin
Metal is 2nd/3rd row
Strong field ligands
High metal charge
Octahedral splitting is high (tetrahedral is …)
Tetrahedral splitting is low = square planar
How to know if complex is high spin
Metal is 1st row
Weak field ligands
Low metal charge
Octahedral splitting is low (tetrahedral is …)
Tetrahedral is high = tetrahedral
Counting electrons structure (NEUTRAL)
dn metal = n electrons
Total ligands electrons
Overall complex charge: + = -1e, - = +1e
vacant site H
| |
M——(H) —> M=—
B-Hydride elimination:
Cis vacant site
Planar space for alkene
Stable alkene
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
A
/
M —> M + A—B
\
B
Reductive elimination:
Oxidation state= -2
d electrons= +2
Coordinatively saturated
Electron withdrawing groups on metal
A
/
M + A—B ——> M
\
B
Oxidative addition:
Oxidation state =+2
d electrons =-2
Neutral molecule added
Coordinately unsaturated complex
EDG ligands
Pre catalyst —> active catalyst
Thermal or photolysis ligand dissociation
How to selectively increase the rate
Donor solvent for migratory insertion
Less substituted alkene
Conjugated alkene
Increase temperature
Define Productivity
Grams made per mole of catalyst per unit of time
Define Turn over number
Number of cycles catalyst completes in a set time
Nproduct / Ncatalyst = TON
Define Turn over frequency
Moles of product by moles of catalyst over time
TON / time = TOF
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.
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)
