High-Oxidation-State Palladium Catalysis

报告人：刘槟 2010年 10月 23日

Introduction• In 1986 , the first unequivocal trialkylpalladium(IV)

complex, [PdIMe3(bpy)],was isolated and characterized by X-ray analysis.

N

N

PdCH3

CH3

CH3I

N

N

PdCH3

CH3

CH3

I H3C-CH3

N

N

PdCH3

I

Acc. Chem. Res. 1992,25,83-90

Advantages• Some advantages compared to Pd(0)/Pd(II) catalysis:

1. Pd(IV) species are often resistant to β-H elimination process

2. Pd(IV) species undergo facile reductive elimination. (like C-C bond formation)

3. Pd(II)/Pd(IV) catalyzed reactions are operationally simple and do not require the careful exclusion of air (especially O2) and moisture.

Chem. Soc. Rev., 2010, 39, 712–733

C-C CouplingR

I

+ + 2R'I + H2C CHY

Pd cat.K2CO3 , DMA

20oC , 30h

R

R'R'

CH

CHY

+

Angew. Chem., Int. Ed., 1997, 36, 119

PdoL2 I R

RPdI

L

L

R

PdI

L

LK2CO3

KI

Pd RL L

R'I

Pd RL I

L

R'

R

PdI

L

L

R'

K2CO3

KIPd RL L

R'

R'I

Pd RL I

L

R'

R'

R

PdI

L

L

R'

R'

RPdI

L

L

R'

R'

R

R'

R'

H2C CHY

CH2

CH

Y

Pd

I

LL

K2CO3

KI

R'

RR'

HCYHC

NH

Br

+

R'

I

HR R''

Pd(OAc)2tri-2-furylphosphine

Cs2CO3 , norbornene

CH3CN , 90oC , 16hn

NR

n

R'

R''

PdoL2

COOMeI

COOMeIL2Pd

PdL2I

COOMe

Cs2CO3

CsI+CsHCO3

Pd

COOMe

L L

N Br

Pd

COOMe

L Br

L

N

NPdL2X

N

COOMeL2Pd

X

Cs2CO3

CsI+CsHCO3

N

COOMe

J. AM. CHEM. SOC. 2005, 127, 13148-13149

Me

I + Ph Ph

Pd(OAc)2norbornene

K2CO3 , n-Bu4NBr82%

Me

Ph PhMe

Me

I + B(OH)2

Pd(OAc)2norbornene

K2CO3 ,DMF88%

Me

Ph Me

Me

I + R

Pd(OAc)2norbornene

K2CO3 ,DMF

Me

MePh

Chem. Soc. Rev., 2010, 39, 712–733

NH + I

BF4-

5 mol% PdII

AcOH , 25oC N

Pd(OAc)2 49% , 5minIMesPd(OAc)2 86% , 18h

NR +

I

R'

Pd(OAc)2 , PPh3

CsOAc , DMA125oC , 24h

NR

R'

(a) Pd0/II Catalytic Cycle

Pd0

+

Ar I

PR3

PdIIR3P

R3P

Ar

I

Electron Rich

SLOW

ElectrophilicPalladation

NH

PdIIR3P

R3P

Ar

N

NAr

-Pd0

(b) PdII/IV Catalytic Cycle

PdII(OAc)2

ElectronDeficient

FASTER?

ElectrophilicPalladation

NH

PdII OAc

N

[Ar2I]BF4 PdII OAc

NAr

-Pd0

Pd0/II versus Proposed PdII/IV Mechanism for Indole Arylation

J. AM. CHEM. SOC. 2006, 128, 4972-4973

carbon-carbon bond formation from unactivated alkyl C-H bond

N

NH

O

Me

+ p-MeOC6H4I

5 mol% Pd(OAc)2AgOAc

150oC , no solvent

N

NH

O

Me

MeO

J. AM. CHEM. SOC. 2005, 127, 13154-13155

N

NHBn

OPd(OAc)2

N

N

O

PdBnAcO 2

1. ArI2. C-H activation

OR1. C-H activation2. ArI

N

N

O

PdAr

IL

red. elimination

protonationligand exchange

N

HN

O Ar

Mechanistic Considerations

N R

Ph2Si(OH)Me

Pd(OAc)2 (cat.)Cu(OAc)2 (oxidant)

DMF , 100oC

N R

N

O

O

N

Pd

Ph

OAcO

O

Ph2Si(OH)Me

N

Pd

Ph

O

O

C-H ActivationPd(0)Ln

Pd(II)Ln

N

O

O

J. AM. CHEM. SOC. 2002, 124, 13372-13373

C-O and C-X Bond Formation

N

5 mol% Pd(OAc)2

75-100oC NX

PhI(OAc)2 , MeCN X=OAc , 86%PhI(OAc)2 , MeOH X=OMe , 95%NBS , MeCN X=Br , 93%NCS , MeCN X=Cl , 95%

N

[PdII] DirectedC-H Activation

NPdII

L

L

PhI(OAc)2

Oxidation

NPdIV

L

L

OAc

L

-[PdII] ReductiveElimination

NAcO

J. AM. CHEM. SOC. 2004, 126, 2300-2301

J. AM. CHEM. SOC. 2006, 128, 7134-7135

RNHTf

Pd(OTf)2-2H2ONMP , DCE ,120oC

N FOTf

RNHTf

F

J. AM. CHEM. SOC. 2009, 131, 7520–7521

C-N Bond Formation

O

O

TsHN

Z:E=10:1

10 mol% Pd(OAc)22 eq. PhI(OAc)2

1 eq. Bu4NOAcMeCN , 25oC , 7h OAc

OTsN

O

92% yield , 9.5:1 dr

O

O

TsHN

10 mol% Pd(OAc)22 eq. PhI(OAc)2

1 eq. Bu4NOAcMeCN , 60oC , 2.5h OAc

OTsN

O

65% yield ,>20:1 dr

PdIIX2

PdIIX

OTsHN

O X

O

O

TsHN

PdIIX

OTsN

OB:

BHX

PdIV(OAc)X2

OTsN

O

OAc

OTsN

O

PhI(OAc)2

PhI

Proposed Catalytic Cycle

J. AM. CHEM. SOC. 2005, 127, 7690-7691

Domino Catalysis Involving Pd(IV) Catalysts

O O

Ph 5 mol% Pd(OAc)26 mol% bipy

1.1eq PhI(OAc)2O

HO

Ph

O

X

Ph[PdII]

AcOHX

OAcR

[PdII]

X

OAcR

Oxidant

Nu

X

OAcR

PdIV

Nu

Oxidant

Nu

X

OAcR

PdIVNu

80oC , 5h AcOHO O O O

OAc

Ph

AcO

Ph

OAc

(79%) <5% Observed <5% Observed

J. AM. CHEM. SOC. 2007, 129, 5836-5837

O

HOAc

Ph

O

Me

[PdII]O O

Ph

O O

PdIIPh

OAc

O

OAcPhPdII

MeH

OO

OAcPh

O

HMe

PdII

O

OAcPh

O

HMe

PdIVOAc

hydrolysis

O

HO

Ph

O

Me

PhI(OAc)2

PhI

O

OAcPh

O

[PdII-H]PhI(OAc)2

ReinsertionOxidative

Functionalization O O

OAc

PhAcO

Proposed Mechanism

First example of enantioselective palladium(IV) catalysis

R1

O O

R2Pd-(i-Pr-SPRIX)

PhI(OAc)2or PhI(OCOCF3)2

O

R2

O

R1

O

up to 95% ee

O N N O

H

i-Pr

i-Pr i-Pr

i-Pr

H

i-Pr-SPRIX

J. AM. CHEM. SOC. 2009, 131, 3452–3453

Problems

1.Little is known about the ligand effect of Pd(IV) complexes

2.Enantioselective synthesis using chiral ligands through Pd(IV) intermediates has not been forthcoming

3.Applications to natural product synthesis are lacking

4.Detailed mechanistic investigation

The development of palladium(IV) catalysis has just begun, it has already enabled the development of a number of significant new transformations. These reactions are marked by their high selectivity and synthetic robustness, and almost all are based on the use of catalysts that are generated in situ from commercially available palladium salts.

Conclusion