Homogeneous Catalytic Processes
RCH CH2 + CO H2
O
H
RCH2CH2+ Co(I), Rh(I) or Pt(II)
Hydroformylation
H2C CH2 O2
OH3C
H
Pd(II) or Cu(II)+
Oxidation
H
CH3OH COOH3C
OH
[RhI2(CO)2]-+
Carbonylation
OH
H2C CH
CH
CH2 2 HCN[Ni{P(OR)3}4]
NCCH2CH2CH2CH2CN+
Hydrocyanation
2 H H 2
HC CH3 Ni(acac)2
CyclotrimerizationHC CH3
Hydrogenation of Alkenes
The most commonly used catalyst is the Wilkinson’s Catalyst
Many alkenes are hydrogenated with hydrogen at 1atm pressure or less
Wilkinson’s catalyst is highly sensitive to the nature of the phosphine ligand and the
Many alkenes are hydrogenated with hydrogen at 1atm pressure or less.
Wilkinson s catalyst is highly sensitive to the nature of the phosphine ligand and thealkene substrate.
Analogous catalysts with alkyl phosphine ligands are inactive
Highly hindered alkenes and ethylene are not hydrogenated by the catalyst
Wilkinson’s CatalystPh3P PPh3 HR CH3 Rh
3 PPh3
Ph3P Cl
HHR
H2
Oxidative AdditionReductive Elimination
RhH PPh3
Ph3P Cl
H
PPh3
RhPPh3
Ph3P Cl
H
PPh3
R
33
PPh3PPh3
Ligand DissociationLigand Association
RhH PPh3
Ph P Cl
HRh
PPh3
Cl
HR
R
Ph3P Cl
RhH PPh3
H
PPh3
Migratory Insertion RRhPh3P Cl
R
Alkene Coordination
Hydroformylation
H2+Catalyst
R
CO+ RCH2CH2CHO
A less common, but more appropriate name is hydrocarbonylation, pp p y y
Both cobalt and rhodium complexes are used as catalysts.
Alk i i ti lk h d ti d f ti f b h d ld h dAlkene isomerization, alkene hydrogenation and formation of branched aldehydes arethe possible side reactions.
Cobalt catalysts operate at 150 ºC and 250 atm, whereas Rhodium catalysts operate atmoderate temperatures and 1 atm.Rhodium catalysts promotes the formation of linear aldehydes. Cobalt catalysts do so ifmodified with alkylphosphine ligands.
HydroformylationC (CO) + HCo2(CO)8 + H2
HOC COCH3CH2CH2CH2CHO COCoOC CO
OC CO
HH
CO
CH3CH2CH2CH2CHO COLigand DissociationReductive Elimination
Co
COOCOC
CoOC COCH2CH2CH2CH3
OC H
CO
COOxidative Addition
H
COC CO
O CH2CH2CH2CH3
H2 Alkene Coordination
Co
COOCOC
CH2CH2CH2CH3
CoOC CO
OC CO
COMigratory Insertion Ligand AssociationLigand Association
CoOC CO
OC COCOMigratory Insertion
Migratory Insertion
Monsanto Acetic Acid Synthesis
All three members of the group 9 (Co, Rh and Ir) can catalyze this reaction.g p ( , ) yA cobalt complex was initially used, which was replaced with the rhodium complexlater on.
Methanol initially reacts with hydroiodic acid to give methyliodide and H2O.Methyliodide reacts with the 16e- catalyst, which forms the rate-determining step.
The final product formed after the catalytic cycle is acetyl iodide, which is hydrolyzedb ater to acetic acid and HIby water to acetic acid and HI.
Monsanto Acetic Acid Synthesis
RhI CO
I CO
CH3ICH3COI
CH3I CH3
Oxidative AdditionReductive Elimination
RhI CO
I CO
3
RhOC CO
I CO
CH3
I
Sol CH3
I
Migratory Insertion
RhI CO
I CO
I
COMigratory Insertion
I
Alkene Polymerization
If only a few monomers couple together, the short chains formed are called oligomers.
Initiation
Propagation
Termination
Alkene Polymerization
The commonly used catalyst has a tetrahydrofuran molecule occupying the fourthcoordination site of zirconium.
Ziegler-Natta Catalyst
Karl Ziegler in 1953, discovered a catalyst based on TiCl3 and AlCl3 for thepolymerization of ethylene.Giulio Natta extended the method for the polymerization of other olefins like propylene
d d b f diff t i tiand made a number of different variations.The Ziegler-Natta catalyst family includes halides of titanium, chromium, vanadiumand zirconium, typically activated by aluminum halide compounds.
Ziegler and Natta received the Nobel Prize in Chemistry in the year 1963.
Alkene Metathesis
Alkene Metathesis
Alkene MetathesisNobel Prize in Chemistry 2005Nobel Prize in Chemistry 2005.
Ring Closing Metathesis
Ring Opening Metathesis Polymerization
