Chiral Azolylphosphines: Synthesisaci.anorg.chemie.tu-muenchen.de/research/hydroform.pdfpropene...
Transcript of Chiral Azolylphosphines: Synthesisaci.anorg.chemie.tu-muenchen.de/research/hydroform.pdfpropene...
Why azolylphosphines?
NP
NN• exceptional π-acceptor properties• very resistant against hydrolysis and oxidation
Moloy, Peterson: J. Am. Chem. Soc. 117 (1995) 7696-7710
How to gain chirality?
PCl3
NH1 equivalent 2 equivalents
PClCl
N PNCl
N
exc. NEt3 exc. NEt3
• stoichiometric reaction yieldingdesired precursors for synthesis of chiral ligands
• also applicable for benzo-annelated derivatives of pyrrol
Chiral Azolylphosphines: Synthesis
→→ chirality by substitution of chlorine with various nucleophiles
W.A. Herrmann, F.A. Rampf (1997)
• screening of various ligands
• rhodium complexes of chiral ligands
• styrene as model substrate
OP N
N
OP
N
N
O
P
O
N
1
2
T = 40 °C, p = 100 bar, t =16 h, toluene
→→ 1 bidentate ligand with moderate stereoselectivity→→ 2 monodentate ligand with significant ee
ligand conv.
[%]
iso / n ee
[%]
1,
[L]/[Rh] = 263 2 40
2,
[L]/[Rh] = 582 6.4 23
Chiral Azolylphosphines: Catalysis
W.A. Herrmann, F.A. Rampf (1997)
Chiral Ferrocenyldiphosphines: Synthesis
electrophile (after lithiation) nucleophile
H
C H 3
N M e 2
F e • modular assembly• 2-step reaction• chiral ferrocenylethylamine +
chlorophosphine (electrophile) + secondary phosphine (nucleophile)
→→ independent introduction of two sterically and electronically different phosphine atoms
• enantiomers applied in various catalytic reactions
• excellent stereoselectivity (e.g. rhodium-catalyzed hydrogenation)
How to gain chirality?
Why ferrocenylphosphines?
W.A. Herrmann, F.A. Rampf (1998)
Chiral Ferrocenyldiphosphines: Catalysis
• first application in asymmetric hydroformylation
• rhodium-catalyzed conversion of styrene
T = 100 °C → 57 % ee (47 % conv) #
T = 60 °C → 50 % ee (26 % conv) #
T = 50 °C → 75 % ee (8 % conv) #
→→ significantly high ee in Rh-catalyzed hydroformylation
# toluene, p = 100 bar, L/Rh = 2, t = 16 h
Cy2P
Fe
Ph2P
H
Fe
Ph2P(o-An)2P
H
W.A. Herrmann, F.A. Rampf (1998)
Rapid Ligand Screening: Autoclave Design
Autoclave assembly for “high-throughput screening”
• sample volume: 1 mL each
• amount of catalyst: 1 µmol each
• pressure range: 1 - 140 bar
• temperature range: 25 - 100°C
• sample preparation: drybox
• 14 samples in each run
→→ novel equipment for “high-throughput screening”under high pressures
W.A. Herrmann, F.A. Rampf (1998/99)
Rapid Ligand Screening: Fe-diphosphines
→→ results in 4 instead of 28 days
→→ fast assessment of T-/basicity trends
Fe
R2PR‘2P
H
leastbasic
mostbasic
40°C50°C
60°C75°C
0
20
40
60
80
100
con
vers
ion
[%
]
catalysts
T
W.A. Herrmann, F.A. Rampf (1999)
A Theoretical Approach to Activity
Comparison of Rh- and Ir-catalyzed hydroformylation
• every step of the hydroformylation cycle calculated in terms of reaction energy
• method: hybrid DFT approach (B3LYP)• no solvent effects• PH3 as model ligand
→→ iridium: thermodynamic and kinetic restrictions for change of coordination number and oxidation state(in accordance with experiments)
⇒ not preferable for hydroformylation, better in hydrogenation
W.A. Herrmann, D. Gleich, R. Schmid (1997/98)
A Theoretical Approach to Regioselectivity
→→ experimentally observed trends could be reproduced→→ explanation limited by parallel steric and electronic effects
ligand substrate method
PH3
propene
3,3,3-trifuorpropene
styrene
hybrid DFT approach
(B3LYP)
DIPHOS propene combined QM / MM
BISBI propene combined QM / MM
}
PPh2
PPh2
PPh2
PPh2
DIPHOS BISBI
W.A. Herrmann, D. Gleich (1998/99)
A Theoretical Approach to Stereoselectivity
→→ stereoselectivities with different ligands could be explained in full agreement with experiments
→→ prediction of stereoselectivities still unsatisfying
• combined QM / MM method
• theoretical requirement of synchronous asymmetric inductions
C2-symmetry in chelating ligand:
C1-symmetry in chelating ligand:
synergetic or antagonistic coupling of ligand backbone - substrate influences
• advantage of restricted coordination possibilities
• drawback of minor stereodifferentiation
W.A. Herrmann, D. Gleich (1998/99)
Outlook: Theoretical Studies
Activity:
consideration of solvent effects withab initio molecular dynamics
Regio- and Stereoselectivity:
development of new methods in order to describe steric and electronic effects in
parallel
Biphasic Kinetics and Mechanism
• biphasic operation mode
• continuously operating mini-plant
• mass-balance available
Neueres Foto folgt noch !
• variable reaction conditions
• high-pressure IR spectroscopy
• controlling by computerW.A. Herrmann, J. Scheidel (2000)
Outlook: Surface Active Ligands
• „dendrimeric” phenylphosphines
• mono- and bidentate ligands
• synthesis successfull
• catalytic testing underway
n = 0, 1, 2
W.A. Herrmann, J. Shi (2000)
(Ph)nPN
N
N
NR2
NR2
NR2
3-n
NR2