Asymmetric Hydrovinylation
Transcript of Asymmetric Hydrovinylation
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Asymmetric Hydrovinylation
Jeff KallemeynJuly 15, 2003
*+Ni or Pd
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Olefin Polymerization
Ziegler (1953)
…then one day...
+ Et3Al100 oC
+ Et3Al Al n
n
n
n up to 125
100 oCnHO
Attributed to cleaning centrifuge with H2SO4… leaving Ni salts behind
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Applications of Ni Catalysts
Keim, Angew. Chem. Int. Ed. 1990, 235.
Nickel catalyzed dimerization of butadiene Shell Higher Olefin Process (SHOP):
“NEODENE (SHOP) alpha and internal olefins areavailable directly from Shell in marine ships andbarges, rail and road tank cars” www.shell.com
NiCl2
PPh2
OH
O80-140 oC
<0.05 mol %
70-140 atmn
n = 0-9
C6-C22
Nickel Catalysts are Used Widely
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Hydrovinylation
*
+
+ +
+ +
* *
+ higher oligimers
Ibuprofen Naproxen Ketoprofen
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Mechanism: Initiation
Bogdanovic, Adv. Organometallic Chem. 1979, 105.
Evidence for Ni-H intermediate
Ni(acac) Et3Al2Cl3 +
8 5% yie ld
No evolution of H2 is observed1)
3) Deuterium incorporation into products when D4 ethylene is used
2) Ni-H detected by NMR analysiswhich disappears upon addition of ethylene
Isolated
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Mechanism: Catalytic Cycle
RajanBabu, Chem. Rev. 2003, ASAP
Evidence for 11 as catalytic resting state. (DiRenzo Ph.D. thesis (Brookhart))
Lewis acid (Y) creates coordinatively unsaturated Ni species.Phosphine ligand (P) influences relative rates of dimerization (hetero- and homo-),
oligimerization and isomerization.
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Reaction Course
Kawata et al. Bull. Chem. Soc. Jpn. 1974 413.
+Naphthyl(Ni)Br(PPh3)2
BF3 OEt22.6 mol%
0 C0.7 atm
°
91% selectivity for desired product
•ò
Å ƒ
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Pressure and Lewis Acid Effects
Kawata et al. Bull. Chem. Soc. Jpn. 1974 413.
+Naphthyl(Ni)Br(PPh3)2
BF3 OEt22.6 mol%
0 C0.7 atm
°
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Temperature Effects
Monteiro, Tetrahedron, 2000, 7403
+[Ni(MeCN)6][BF4]2
PPh3Et2AlCl10 atm
} Styrene polymerization
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Influence of Ligand
RajanBabu, Chem. Eur. J. 1999, 1963.
Ligand effect is largely steric in nature
Larger R on phosphine disfavors coordination of second styrene over ethylene.
R = i-Bu gives more dimerization than R = Bn
X
PNi R
RR
CH3
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Asymmetric Hydrovinylation
Wilke Angew. Chem. Int. Ed. 1988, 186
+[allyl-NiBr]2 0.05 mol %Et3Al2Cl3 0.15 mol %
ligand-60 C, 2.5 h1 atm
93% yield97% ee (R)
Isolated active component from mixture
Changing from (R)-phenylethylamine (RR ligand) to (S)-phenylethylamine (RS ligand) gives poor ee’s (6%)
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Counterion Effects
RajanBabu, JACS 1998, 459.
Al Lewis acids can cause problems with Lewis basic substrates
i) [(allyl)NiBr]2 (0.35 mol %) PPh3 AgOTf -55 oC 2h
ii) [(allyl)NiBr]2 (0.7 mol %) (R)-MOP 8a NaBARF -56 oC 2h
iii) [(allyl)NiBr]2 (0.7 mol %) (R)-MOP 8b NaBARF -56 oC 2h
CF3
CF3B 4Na
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Hemilabile Ligands
RajanBabu, JACS 1999, 9899.
Hydrovinylation of Styrene
1H NMR studies show instability of (allyl)Ni5a complexeswith Br, OTf, SbF6 and BARF counterions.
(allyl)Ni5cBARF complexes are highly stable (rt for 2 days)
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Stereochemical Determining Step
Enantiotopic face of styrene chosen at this step.Resulting allyl complex assumed to be stable
through remainder of steps.
X
H P
ONi
R
R
H should be cis to P due to sterics and ligand directing
Coordination of styrene
Transfer of H, face is selected from steric influences of P(R)
P
ONi
R
R
CH3
H H
H P
ONi
R
R
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Phosphoramidite Ligands
Leitner, JACS 2002, 736.
Modular Ligands Show Promise
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Tunable Ligands
RajanBabu, JACS 2002, 734.
No activity:
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Palladium Catalyzed Hydrovinylation
Vogt, J. Organometallic Chem. 1998, 187.
Isomer Yield27182321
IsomerYield10913141857
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Palladium Catalyzed Hydrovinylation
Granell, Organometallics, 1999, 3511.
+
[Pd(2-Meallyl)(PBnCyPh)]BF4
0.1 mol %15 atm
Isomerization major drawback to Pd catalysts
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Ruthenium Catalyzed Hydrovinylation
Yi, Organometallics, 2001, 802.
No asymmetric examples
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Ruthenium Catalyzed Hydrovinylation
Yi, Org. Lett. 2003, 1567.
Lack of methods for preparation of (S) side chain in vitamin D analogs
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Applications of Hydrovinylation
Leitner, Chem. Comm. 1999, 1583; Angew. Chem. Int. Ed. 2001, 2697.
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Conclusion
Nickel catalysis are the most developed.
Low catalyst loadings are amenable to industrial procedures.
Atom economical.
Terminal alkene is a good handle for additional chemistry.
Method limited in the short term to conjugated dienes.
Use in fine chemical synthesis will require additional ligand development.
Poor understanding of the factors that influence side reactions --(Isomerization, Dimerization and Oligimerization)
*+Ni or Pd
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Other Substrates
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Propene
RajanBabu, Tetrahedron 2000, 2145
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Influence of Ligand on Propene Dimerization
Ref
isomersallyl NiCl[PCH3]3
EtAlCl2
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Influence of Ligand on Propene Dimerization
Ref
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Oligimerization and Isomerization
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Tolman Chem. Rev. 1977 313