2011/8/7 Yoshino (D1)
Organometallics Study Meeting
Chapter 11. Nucleophilic Attack on Coordinated Ligands

11.1 Fundamental Principles
General Tendency
NuX
M
YX
YMor+NuorM X

M X YNuM X Yor

Y Nu

Weak Electrophiles

Favored by•Coorinatively saturated metal center• -accepting ancillary ligands•Electron-poor metal center•Cationic metal complexes•Sof t nucleophiles

Nu

Strong Electrophiles
MCORM

YX

Intermediates in ligand substitution (Chap. 5)

Due to "net flow of electron density to metals"

M CORElectron Number and Oxidation StateM

Electron NunmerOxidation State of M

No change

No change

No change

No change

No change–2M+ Nu

NuO
M C O + Nu

MMNuM+ Nu

Nu

11.2 Nucleophilic Attack on Transition Metal Complexes of Carbon
Monoxide and Isonitriles
11.2.1 General Trends
O
LnM CX+ Nu

LnM

X = O or NR

Nu

Reactivity gets higher in the case of...
•Weak back donation•M is cationic•L is less donating and more -accepting

As guideline, complexes which has

CO values below ~2000 cm-1

are relatively inert.

11.2.2 Examples of Nucleophilic Attack on Carbon Monoxide and Isonitriles
Alkyl- and AryllithiumO
RLi + M(CO)nR

O
M(CO)n-1

R

OR'E+M(CO)n-1

R

M(CO)n-1

E+ = R'OTf, R'3OBF4'+E

M = Cr, Mo, W (n=6)
Fe (n=5)
Ni (n=4)

O
R

O
M(CO)n-1
R'R+R'

M(CO)n-1
E+ = R'X, R'OTs

1

Hydroxide Alkoxides and AminesO
M CO + OH
dnM

Important in some industrial processes and water gas shift.

–CO2OHM H
dn+2OHM2– + H2OO

[Fe(NO)(CO)2(PPh3)2]+ MeO(Ph3P)2(CO)(NO)FeOMe

O+ R2NH2

LnM CO + 2 R2NH

LnM

Example of Isonitrile
ClIn general, isonitrile is less reactive than CO as an electrophile.

PPh3PdCl

NHR2ClCNR

PPh3Cl+ClH
C NR
NH2PhPd

PhNH2PdCl

PPh3
NHR
NHPh

11.3 Nucleophilic Attack on Carbene and Carbyne Complexes
Cp
OC FeOCCp
MeLi

OMe
HOMe

PMe3(CO)5W
MeOC FeOCHNuPh

This type reaction is limited tocanionic Fischer carbenes
or neutral Fischer carbenes with the ligands
which stabilize negative charge.

OMe(CO)5W
PMe3
MeOMe(CO)5CrOMeMeOMe
PhNu(CO)5Cr–MeO

Nu(CO)5CrPh

Nu = RS , R2NH, PhLi

11.4 Nucleophilic Cleavage of Metal-Carbon -Bonds
11.4.1 General Principles and Trends
General Scheme
MLn R +dn

MLn +Nu•M is reduced by two.
•Retro reaction of some SN2 type oxidative addition.
•Uncommon in catalytic process.
•R=alkyl : Slower than addition to CO, carbene, olefins.

NuR

dn+2

Reactivity
O
LnM

LnM<LnM

rare or unknown

LnM CR3RAcyl-M is less reactive thancorresponding esters, amides or ketones.

<Mcommon2

11.4.2 Examples of Nucleophilic Attack on -Bound Ligands
Attack to Metal-Alkyl Complexes
RHPh

LnPd(0)RPd(II)LmH +Ph

LnPd(II)

Racemization mechanims ofchiral Pd-alkyl complexes

LmPd(0)I
Ph2 MeP
MePt
MeP
Ph2 I

Ph2 MeP
MePt
MeP
Ph2

MeI +

Favored in
more polar solvent

Reductive elimination fromPt(IV)-Me complex.

MePt
MeP
Ph2

This type reductive elimination isknown in C-H functionalizationof alkanes and proceed withstereoinversion.

Faster inless polar solvent

XH

XH

H N
N
Rh
NN

Ph2
PX

X
base

N

XH = NHTs
OH
ligand =CH2NO
tetraphenylporphine

NNRh

NN

N+Rh

NN

N

NRh

N

N

Attack to Metal-Acyl Complexes

ArX

LnPd(0)

O

Ar
LnPd

COLnPd

X

Ar

Ar

LnPd

M = R3Sn, ZnX, BX2

X

LnPd(0)+O

O

R'M : Attack to metal

R'
Ar

NHR'R''
Attack to ligand2

11.5 Nucleophilic Attack on
11.5.1 General Trends

Ar

NR'R''+LnPd(H)X

base–HX

LnPd(0)-Unsaturated Hydrocarbon Ligands

Electrophilic

Mvs.

M
Cationic,
electron-poor neutralor higher valentOlefins are generally
nucleophilic.

O-elimination

H O NR'R''
ArLnPdXR'

Nucleophilic
LnM
Anionic,
electron-rich neutralor lower valent

Reactivity of Several Unsaturated Systems>>>

Even System >>> Odd System
Open System > Closed System>

>>>

>

>

>

Studied about cationic 18 electron complexes
and guidelines were developed by Davies, Green and Mingos.
3

2

11.5.2 Nucleophilic Attack on-Olefin Complexes
211.5.2.1 Overview of Nucleophilic Attack onRM

•Well known for Pd(II), Pt(II), Fe(II)•Forming M-alkyl complexes•Nucleophilic attack occurs at the opposite face of olefin to metal..
•Nu generally attack more substituted carbon (many exceptions)•Most examples are limited to mono- and disubstituted olefins.

R

Nu-Olefin Complexes

Nu
M

Mechanism and Regioselectivity

R

12

C
H

Nu
R

Nu

H

C

M

1C

H

H

H

Nu

H

R

H
H

2CM

M

H

C1-M > C2-M
C1 is more cationic than C2
2

11.5.2.2 Specific Examples of Nucleophilic Attack on-Olefin Complexes

Reaction with Cationic Iron(II) Complexes
Cp R

CpNu

OC FeOCROC FeOCStereochemistry : transRegiochemistry : depends on nucleophiles

Nu

Nucleophiles : MeO , tBuS , Ph3P, (EtO)3P, R2NH, CH2NO2, Active methylenes, enamines, LiCuMe2

Reaction with Pd(II) Complexes
In Pd(II) cases, stabilization by chelation is necessary to avoid -elimination and isolate -alkyl complexes.
Nucleophilic Attack occured at the oposite face to the Pd.
NMe2Nu+ Li2PdCl4 + NuPdClN
Me2

Nucleophiles : MeO , CH(CO2Et)22

Many catalytic reactions include this type nucleophilic addtion.
Pd(II)

Pd(II)
NHTs[ox]NTsNTsNTsPd(II)-H

Also catalytic addition of active methylene to olefin has been reported.
OOOMePdCl(CH3CN)

OMeD
DOOH O–HCl

DDPdO
H
D

DO
OMe

O
OMeHClD
D

PdCl(CH3CN)

4

11.5.3 Nucleophilic Attack on Square Planer Pd(II)Diene and Allene Complexes
2Dienes can bind to metals in bothand4

fasion and this section describe the reaction ot theOMe

NaOMePdLiCl, LiOMe

AcOcomplexes.

OMe

AcOH

[Pd]
Pd(OAc)2 (cat)benzoquinone

AcOOAcOAc

AcO
LiOAc, AcOH
with or witout LiCl

2with LiCl

without LiCl

11.5.4 Nucleophilic Attack on

In the absence of LiCl
second attack occured intramoleculary.

2-Alkyne Complexes

2-Alkyne Complexes which are cationic or have high oxidation state are highly reactive.
Cp

Various nucleophiles could raect to form trans olefin complexes.

Cp

OC FeL

OC Fe
L+ Nu

11.5.5 Reactions ofTp

Nu These processes are included
in many late metal catalyzed reactions.

2-Arene Complexes

Reaction as diene
2OC ReL-Arene complexes often react as dienes,
not as electrophilic olefin complexes.

11.6 Nucleophilic Attack on Imine and Aldehyde Complexes
Coordination of imines and aldehydes to Lewis Acid enhances the electrophilicity
and most reactions proceeded from 1-complexes rather than 2-complexes.

11.7 Nucleophilic Attack on Polyhapto ( 3- 6) Ligands
11.7.1 Nucleophilic Attack on3

Reactions of Pd(II) Complexes

Nu : Stabilized carbanions, amines etc.

Pd(0)
Nu

Pd-Allyl Complexes

NuPd(II) complexes tend to react at less substituted carbon.
Important process in allylic substitution reactions andregio- and stereoselective reactions are well studied
using Pd, Ir, Mo, W, Ru catalysts. (Chap. 20)

Reactions of Isolated Allyl Complexes
CpCp

OC MoONOC MoON

Nu

Nu

Regiochemistry : Attack to the carbon trans to CO ligand(stronger transinfluence)
Stereochemistry : Attack to the opposite face to metal

In general, ligands with strong donation and transinfluence lengthen M-C(allyl temini) bondlocated at trans position to result in higher reactivity. Regiochemistry is controllable by electronic factor.
5NaCH(CO2Me)2MeMePdCl2
82% eeMePh+PPh3, benzene, rt

Ph

Ph

MeO2C

CO2MeMePh

PhMgBrPPh3, Et2O, rtMeO2C

Ph

86% yield
79% eeCO2Me inversion (attack to ligand)

94% yield
59% eeretention (attack to metal)

Reactions at Central Carbon of Allyl Group
Cp

MeLi

Mo

LUMO mainly consists of metal d-orbital andallyl *-orbital in less common cases.
In those cases, reaction proceeds at central carbon.
(Common : d-orbital and allyl non-bonding orbital)

CpMo

CpMeCpCpLM( 3-allyl)+ (L=CO, PR3; M=Co, Rh, Ir) also tend to react at central carbon.

11.7.2 Nucleophilic Attack on

4-Diene Complexes

Reactions of Cationic Mo- 4-Diene Complexes
MeMeMgBr

HMo
OC

Mo
OCCO

CO2H
MeI2OHMo
OC

H
O
O

CO+Mo
COOC

COCp

Cp+H
R kineticallyfavoredR

25 °C

OC(CO)3Fe< 0 °C

Fe(CO)3Mo

Me–78 °C
R

MeH
CO2Et

Cp

Reaction of Iron Complex

CO2Et

CH(CO2Et)2hydride
abstraction

COCp

Cp

HO2C

MePh3C+

EtO2C+H(CO)3Fe

R

R

thermodynamicallystable11.7.3 Nucleophilic Attack on
Reaction of Cp Ligand

Rh+ PhLi

5-Dienyl Complexes

PhRh
Et2O
rtAlthoug Cp is the most common ligand in this class,
only strong nucleophile can react.

6Reactions of Fe(CO)3 Dienyl Complexes
Hor

Nu
CPh3

Fe2(CO)9Nu

Fe(CO)3Fe(CO)3Fe(CO)3
Nu'Nucleophiles : organolithium, -copper, -zinc,enolates, amines, indole, etc

11.7.4 Nucleophilic Attack on

NuNu'1) CPh3

NuR3NO

2) Nu'Fe(CO)36-Arene Complexes
6-Arene Complexes

11.7.4.1 Overview of Nucleophilic Attack onMore electrophilic
Benzlylic cations
and anions arestabilized.

Regioselectivity was complicated andaffected by stereo and electronic factors ofsubstituents (usually ortho is disfavored.).

MLL

In many cases, addition is reversible andproduct is not kinetically controlled.

Sterically blocks
attack below the arene.

Only strong nucleophiles (organolithium,Grignard reagents) can add irreversibly.

LR
Cl+ClRR

R
Cl+ Cl+Cr(CO)3Cr(CO)3Cr(CO)3R

Cl+Cr(CO)3Cr(CO)3–Cl

Prepared by heating or mixing
arene and metal carbonyl or cationic metal precursors.

RCr(CO)3

Catalytic process of addition or substitutions have been not reported yet.
In general, free arenes are released by oxidation.

11.7.4.2 Examples of Nucleophilic Attack on

6-Arene Complexes

Additions to Arene-Cr(CO)3
R+Cr(CO)3

Unreactive : LiCH(CO2R)2, LiCH2COR, MeMgBr, tBuMgBr,
Me2CuLi, vinyllithium

RCr(CO)3

Reactive :LiCH2CO2R, LiCH2CN, KCH2CO2tBu, LiCH(CN)OR,LiCH2SPh, Li-1,3-dithiane, PhLi, Li acetylide, allyllithium

Reactivity of arene : PhCl (o, p) > PhCH3 (m), PhOMe (m)7Other Examples
Similar reactions are also studied with (arene)CpFe+ and (arene)Cp*Ru+
There are several examples of application to synthesis of complex molecules.

Cl

RuCp

Cl

PF6OMeOH+HN
BocHN

CO2MeHN
BocHN

O
CONH2O

CO2R
NHCbz

CONH2OMeO

2,6-ditBu-phenol

CO2Me

RuCp

PF6

OR1O
h

RO2C
Cbz

HN
NH

BocHN

CO2MeO

H
N

CbzHN
O

CONH2R2O
N
CO2MeH
CONH28