Chiral Azolylphosphines: Synthesisaci.anorg.chemie.tu-muenchen.de/research/hydroform.pdfpropene...

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Why azolylphosphines? N P N N • exceptional π-acceptor properties very resistant against hydrolysis and oxidation Moloy, Peterson: J. Am. Chem. Soc. 117 (1995) 7696-7710 How to gain chirality? PCl 3 N H 1 equivalent 2 equivalents P Cl Cl N P N Cl N exc. NEt 3 exc. NEt 3 stoichiometric reaction yielding desired 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)

Transcript of Chiral Azolylphosphines: Synthesisaci.anorg.chemie.tu-muenchen.de/research/hydroform.pdfpropene...

Page 1: Chiral Azolylphosphines: Synthesisaci.anorg.chemie.tu-muenchen.de/research/hydroform.pdfpropene 3,3,3-trifuorpropene styrene hybrid DFT approach (B3LYP) DIPHOS propene combined QM

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)

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• 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)

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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)

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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)

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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)

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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)

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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)

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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)

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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)

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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

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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)

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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