1. Homogeneous Catalysis HMC-4- 2010
Dr. K.R.Krishnamurthy
National Centre for Catalysis Research
Indian Institute of Technology, Madras
Chennai 1

2. Homogeneous Catalysis- 4
Hydroformylation
Oxo reaction
Reaction of CO and H2 with terminal alkene
Production of n-butyraldehyde, butanols, C6- C9 alcohols & Long-chain fatty alcohols

3. Hydroformylation- The beginning
Journey from Fischer- Tropsch to Hydroformylation / Oxo reaction

4. Discovery of Hydroformylation

5. Hydroformylation- Discovery

6. Hydroformylation-History
1938 Otto Roelen found the Hydroformylation
At first cobalt-catalyst
1965 Wilkinson found rhodium catalyst
1980 process had been upgraded
RCH/RP-process- separation of rhodium from the product
Also named oxo-process
Useful to converting terminal alkenes into other organic products
Carbon chain increased by one
Main industrial application is in the production of butanal from propene

7. Hydroformylation-Applications

8. Oxo process- For plasticizer alcohols

9. Hydroformylation Thermodynamics: Hydrogenation Vs. Hydroformylation
Addition of a H atom and a formyl group to the double bond of an alkene.
Efficient with terminal alkene
R + CO + H2 → R CHO + R CHO
“normal” “iso”
linear product branched product
Thermodynamics: Hydrogenation Vs. Hydroformylation
H2 + CH3CH=CH → CH3CH2CH3
∆G = -88 kJ mol-1
∆H = -126 kJ mol-1
H2 + CH3CH=CH2 + CO → CH3CH2CH2CHO
∆G (1) = -42 kJ mol-1
∆H = -150 kJ mol-1
Though alkane is the thermodynamically more favourable, the actual product
is the aldehyde, because “kinetic” control occurs.
The reaction is highly exothermic and is conducted at adiabatic conditions.

10. 70 years of Oxo synthesis Five quantum leaps of development:
“Diaden process” with heterogeneous cobalt catalysts;
High pressure process with homogeneous Cobalt catalyst;
Introduction of Rh as the central atom of complex catalysts;
The ligand modified Rh or Co catalysts; and
The two-phase catalysis

11. Plasticizer alcohols via Hydroformylation

12. Hydroformylation - Features

13. Preparation of Co complex

16. Hydroformylation of propene with Cobalt catalyst
The inner cycle shows the formation of liner product and the outer cycle the
Branched isomer

17. Cobalt catalyzed hydroformylation- Mechanism
Co2(CO)8 + H2 ⇋ (high pressure) 2[CoH(CO)4]
The complex loses CO to produce the coordinatively unsaturated complex catalyst.
2. The complex catalyst coordinates to the alkene (Propene).
Undergoes insertion reaction → n-alkyl complex (may be branched also).
Propene coordination followed by olefin insertion into metal-H bond in a Markovnikov or anti-Markovnikov fashion gives the branched or the linear
metal-alkyl complex, respectively.
5 At high pressures of CO, the complex undergoes migratory insertion of CO to yield the acyl complex (IR spectral evidence).
6. Attack by H2, as strongly acidic HCo(CO)4 will yield the aldehyde and regenerate.
7. The last step is often rate-determining.

18. Cobalt catalyzed hydroformylation- Mechanism
The catalytic cycle is firmly established.
Both Co(CO)4 (COPrn) and Co(CO)4 (COPriso) have been isolated and
their reactions with H2 as well as HCo(CO)4 have been studied.
There are spectroscopic data and/or strong theoretical arguments in favour
of the existence of all the catalytic intermediates.

19. Hydroformylation- General features
There are two ligands, CO and L = PPh3.
Hydroformylation with Rh can also be effected in the absence of phosphine.
In such a situation, CO acts as the main Ligand.
The intermediate complexes in the catalytic cycle switch from 18e- to 16 e-
complexes
The catalyst precursor undergoes ligand disssociation to generate
coordinatively unsaturated species.
There are two insertion steps (alkene and CO)
The selectivity to n-butyraldehyde is determined in the first insertion step.
This is then followed by oxidative addition step (of H2), which is the rate-
determining step.
Reductive elimination gives the aldehyde and generates the catalyst
General catalyst composition- Hx My (CO)n Ln
Hydroformylation activity pattern with unmodified ligand (n=0)
Rh >> Co >Ir,Ru > Os >Pt >Pd > Fe >Ni
Rh & Co most commonly used; Pt asymmetric hydroformylation

20. Reaction cycle for hydroformylation on Co
Mechanism with long chain olefins, > C3

21. Mechanism on Rh catalysts
Approach of Propylene
leads to isomers

22. Ligand effects

23. Steric effects by ligands

24. Ligand effects
Steric (cone angle bite angle), substituents & electronic factors of ligands
affect the activity & n/i ratio

25. Product selectivity: Linear Vs. Branched aldehydes: Regio-selectivity
Two different ways of inserting an alkene into a metal-hydrogen bond:
H R Anti-
R Rh → Rh Markovnikov
→ Rh R Markovnikov
It is considered to be primarily an effect of steric crowding around the metal center.
The normal alkyl requires less space and therefore formed more easily than the
branched one in the presence of bulky ligands.
Higher selectivity for the linear aldehyde by the addition of alkylphosphine
Replacement of CO by a bulky ligand disfavours the formation of complexes
of sterically crowded 2-alkane
Co(CO)2PBu3 Co(CO)2PBu3
isomerize→ k << 1
CHCH2CH2CH CH3CH-CH2CH3

26. Phosphine derivatives as ligands for Co catalysts
Phosphine derivatives -PR3 – R = C6 H5, n-C4H9
Variations in Gr V elements
Ph3P >> Ph3 N > Ph3 As > Ph3Sb> Ph3Bi; Phosphine ligands –Best choice
Alkyl phosphines
Strong electron donors and thus dissociation of CO is retarded,
Leads to more stable catalysts, but also much slower catalysts.
Aryl phosphines
Do not seem to be very effective ligands.
They are weaker electron donors and form less stable complexes in the
competition with CO
They quickly decompose at higher temperatures.
The more electron withdrawing the aryl group is, the faster the decomposition.
The reported order of activity (195oC, 36 bar)
Ph2EtP > PhBu2P > Bu3P > Et3P > PhEt2P > Cy3P
The linear .Vs. branched ratio decreases as follows:
Bu3P > Et3P = PhEt2P = Cy3P = PhBu2P > Ph2EtP, ranging from 5.5 to 3
N containing ligands like amines, amides & isonitriles show lower reaction
rates due to stronger bonding with metal

27. Rh phosphine complexes are more active catalysts than cobalt complexes
The Rh Catalyst
Rh phosphine complexes are more active catalysts than cobalt complexes
[RhH(CO)(PPh3)3 → [RhH(CO)(PPh3)2] + PPh3
Lower temperatures and Pressures
Higher selectivity to linear aldehydes
Catalyst separation is made easier
Rate expression:
d[RCHO]/dt = k[Rh]a[alkene]b[H2] / [CO]
Value of b depends on the alkene; both a and b may be less than one.
Inverse dependence of rate on the concentration of CO is observed only
at total pressure exceeding 40 atm.
At lower pressures, the rate increases with increase in pressure.
Industrially, a large excess of the phosphine is used, which is necessary
for a good selectivity to n-butyraldehyde.

28. Hydroformylation of propylene with Rh/PPh3- Catalyst cycle

29. Mechanistic insights
In-situ IR and multinuclear NMR studies under less severe conditions:
The oxidative addition of dihydrogen is most likely the rate-determining step
Hydroformylation of CH3 Rh(COR)(CO)4
3,3,dimethyl1-butene C = C – C – C intermediate is seen
CH3 by IR
1-Octene O Styrene O Ph
C C
RhL2(CO) RhL2(CO)2
have been identified by NMR

30. [ ]
No CO, L = 3
[ ]
[ ]
L = PPh3
High selectivity for
n-butyraldehyde
[ ]
[ ]
Anti-Markovnikov
[ ]
[ ]
[ ]
[ ]
Markovnikov
[ ]
[ ]
[ ]
[ ]
[ ]
[ ]
←No L, only CO
HRh(CO)4
[ ]
Schematic drawing of catalytic cycles coupled by substitution of L and CO in Rh catalyst

31. In a typical industrial process, the Rh to phosphorus molar ratio is
between1:50 to 1:100, while the partial pressure of CO is about 25 bar.
All the complexes with the general formula, HRh(CO)nL4-n
n = 0 – 4) might be present with variable concentrations.
In fact, even HRh(CO)4 without any phosphorus ligand can be used as
catalyst.
The selectivity towards anti-markovnikov product increases with more
phosphinated intermediates, whereas more carbonylation shifts the
selectivity towards Markovnikov product.
This is to be expected in view of the fact that sterically crowded
environment around the metal center favours anti-Markovnikov addition
and Yields n-aldehyde (linear aldehyde)

32. Commercial homogeneous Oxo processes
Cobalt catalyzed Hydroformylation is the old Workhorse
The key issue in the hydrofomylation reaction is the ratio of the linear to the
branched products (Regio-selectivity)
Linearity can be influenced and maximized by influencing the kinetics and
changing the ligand characteristics.
Three major process types
The first processes were based on cobalt carbonyl complexes.
The second is the process based on phosphorus modified Co-based
catalyst system developed by Shell.
Third Rh based catalysts - Ruhrchemie/Rhone-Poulenc, Mitsubishi-
Kasei, Union Carbide and Celanese
Supported liquid phase & supported aqueous phase catalysts

35. Oxo processes – The evolution
Process Parameters Cobalt Cobalt Rhodium
Carbonyl +Phosphine +Phosphine
Temperature,oC
Pressure, atm
Alkane formation Low Considerable Low
Main product Aldehyde Alcohol Aldehyde
Selectivity to
n-butyraldehyde
Isolation of catalyst Difficult Less difficult Less difficult:
HCo(CO)4 Water soluble
is volatile phosphine, a
major advancement

36. Oxo processes- Variations

38. Aqueous biphasic catalysis: Ruhrchemie/Rhone-Poulenc Oxo process
In aqueous, homogeneous two-phase catalysis, the active catalyst for the
reaction is (and remains) dissolved in water.
The reactants and the products, which are ideally organic and relatively
non-polar, can be separated off after the reaction is complete by simply
separating the second phase from the catalyst solution, thus making it easy
to recirculate the latter.
Positive influence of water and
Inherent advantages of homogeneous catalysis.
The new oxo process was completely different from the earlier ones :
The catalyst is applied in water soluble form;
The process procedure;
The reactor with special mixing of the two-phases;
The energy balance; and
Simple circulation of the aqueous catalyst solution.
For the water soluble ligands, the price and the performance are the key

39. Water – soluble ligands of Rh
TPPTS: Tri(m-sulfonyl)triphenylphospine, vulgo triphenylphosphine,
trisulfonated

40. Hydroformylation with TPPTS

41. New generation oxo process- Features
High selectivity, producing virtually exclusive aldehydes with up to 96%
linearity;
Simplicity in terms of apparatus and process operation;
Net steam supplier, making excellent utilization of the heat of the reaction
by means of the “heat transfer medium” n-butyraldehyde;
Very simple recycling of the homogeneous oxo catalyst by immobilization
using the “mobile support” water;
Excellent economics owing to minimal losses of the catalyst metal, Rh;
Low purity demands on the reactants;
Excellent process potential from safety and environmental points of view.
Synthesis of TPPTS
Sulfonation of triphenylphosphine: pH controlled selective extraction and
Re-extraction procedures;

42. Further Improvement in ligand synthesis
BISBIS: sulfonated bis(diphenylphosphine)biphenyl, varying grades of
sulfonation;
BINAS: sulphonated NAPHOS, binaphthyl structures
Rh/BINAS is the most active and selective water-soluble hydroformylation
catalyst.
Its reactivity is up to 10 times higher than TPPTS with n/iso selectivities of
98/2 compared to 96/4 with TPPTS

43. Hydroformylation- Process variations

46. The Shell Process Higher alkene feed → Detergent alcohol
Phosphine-modified Co catalyst for production of linear alcohols with C atoms
Important characteristics:
HCo(CO)3(P n-Bu3) is less active for hydroformylation than HCo(CO)4, but more active for subsequent hydrogenation of the aldehyde.
Both hydroformylation and hydrogenation of the aldehyde are catalyzed by the same catalyst.
Phosphorus ligand substituted derivatives are more stable than their carbonyl analogues at high temperatures and lower pressures.

47. Linear alcohols - Chemical considerations
The internal alkenes must be isomerized to terminal one from the thermodynamic mixture, where the terminal alkene will be very small.
The hydrofomylation catalyst must have a very strong preference for the terminal carbon atom to give 60-80% linear products.
HCo(CO)4 is an effective isomerization catalyst.
The terminal alkenes undergo faster or preferential formation of 1-alkyl group or a faster migration of the 1-alkyl group.
The activity of 1-alkene is much higher than that of internal alkenes (1000 times faster).

48. Thermodynamic Vs. Kinetic Pull
Linear Alcohols by Hydroformylation of internal alkenes
Thermodynamic Vs. Kinetic Pull
H2 + CO → Slow→ O
Very fast ↑ ↓ HCo(CO)4
H2 + CO → Fast→ O
Cobalt, once attached to an alkene, “runs” along the chain until an irreversible
Insertion of CO occurs (Chain running).
Alkene does not dissociate from the cobalt hydride during the isomerization process.
Ligand substitution on the Co carbonyl by tert-alkyl phosphines: Shell process
The reaction is a hundred times slower, the phosphine complex is less active;
Hence higher temperatures, 170oC versus 140oC
The selectivity to linear products increases (75-90% versus 60-70%)
The carbonyl complex formed, HCoL(CO)3 is much more stable; Hence the
process is operated at lower pressure ( bar versus bar)
The catalyst acquires activity for hydrogenation

49. Isomerization

50. Other Hydroformylation reactions
1. BASF/Hoffmann-LaRoche;Intermediate for Vitamin A;Rh catalyst without
Phosphorus
2. ARCO; An inermeidate for 1,4-butanediol; Rh with Phosphorus ligand
3. Kuraray; An intermediate for 3-Me1,5-pentanediol; Rh with CO and
4. Mitshubishi Kasei; Isononyl aldehyde; Rh catalyst with PPh3 oxide as a
weak ligand

51. Homogeneous catalysts