Organometallics Study Meeting
Part 4. Reactions of Organometallic Complexes

2011/4/28 Yoshino (D1)
I. 10

1. Basics
1-1. Ligand Exchange
Dissosiative Mechanism–L

MLn+L'

MLn-1

ML'Ln-1

Reaction rate does not depend on the [L'].

Fe(CO)5 (18e) : Photo-promoted dissociation of CO ligand
Associative Mechanism
Common in d8 square planar 16e complex (Pd(II)L4 etc.)

TL

L
M X

Y+YT MLLL
T M Y
Lretention–XX

Trans Effect : Effect of T on rate of ligand exchange
CO, CN–, C2H4 > PR3, H– > CH3– > C6H5– , I– > Br–, Cl– > NH3, H2O
Evaluated using Pt(II) complex
Trans Influence : Parameter indicating how weak T makes M-X bond
H–, CH3–, C6H5– > PR3, CN– > CO, C2H4 > I–, Br– > Cl– > NH3, H2O
YL-Bonding ligands show strong trans effect by stabillizing 5-coordinated structure.

MX

L
Transmetallation
LnM-X + R-M'

M = transition metal
M' = MgBr, BR'2, SnR'3, Cp2ZrCl etc.
X = halides, OAc etc.

LnM-R + M'X

1-2. Oxidative Addition
AGeneral•Oxidation number increases by 2.
•Coordination number increases by 2.

LnM(m+II)

LnM(m) + A-B

B
Low valent, coordinatively unsaturated, electron rich complexes are active in oxidative addition.
Vaska's complex [trans-Ir(CO)(PPh3)2Cl, Ir(I), d8, 16e]ML2 [Ni(0), Pd(0), Pt(0), d10, 14e]

Oxidative Addition to H2
Orbital Interactiion

LPt
L+H2L

HLLL

PtPtHHLH

HOMO energy level increases when L-Pt-L bondbends (up to 90 °).
Bidentate phosphine ligand improvereactivity of oxidative addition.

HPt

L
LUMO
(6s, 6p)

LHPt

HL
HOMO(5d)H*1

Oxidative Addition to C-H, C-C BondCy2
PCH2C(CH3)3Pt–C(CH3)4H
P
Cy2Pt(II), d8, 16e

Cy2PPtP
Cy2Me3P

PhH or CH4Pt(0), d10, 14e

Cp*
Rh

Cy2PRPt
HP
Cy2Pt(II), d8, 16e

Cp*hH
Rh(III), d , 18e

Cp*

Rh

H–H26

R = Ph, CH3

Rh

Me3P

Me3P

Rh(I), d8, 16e

Rh(III), d6, 18e

Oxidative Addition to C-X Bond through SN2 Mechanism
LnM + R-X

LnM

Ph3PPdPh3P

DHR

Metal : Pd(0), Pt(CH3)2, Ir(I) etc.
Halides : Alkyl-X, Allyl-X (sp3 C-X)

[LnM-R]+ X–

X

Br

PPh3+Ph3P H DPd
Ph3P

Br

Br–HPdDPPh3

10

Pd(0), d , 14e

Stereo Inversion at C Center.
Trans Addition

Even 18e complex can react thtough SN2 mechanism.
Cp
Cp
Ir+Ir
Ph3P

COCH3Ir(III), d6, 18e

Ph3P

CO + CH3I

Ir(I), d8, 18e

I–

Allyl-X shows higher reactivity and -ally-complex is formed.
Cy3PPd
Cy3P

Cy3P
OAc

Cy3P

Pd(0), d10, 14eOAc

Pd

Cy3P
Cy3P

HHPd(0), d10, 16e

Cy3P

Pd

Pd–OAc–PCy3

8Pd(II), d , 16e

AcOPd(II), d8, 16e

Oxidative Addition to sp2 C-X bond
Ph3P
Ph3P
Pd +Ph3P

XPd

X

YPd(0), d10, 14e
YReactivity
X : I > Br >> Cl
Y: Electron Withdrawing Group > Electron Donating Group

Oxidative Addition through Radical Mechanism

X

Ph3P

Ph3P

Pd

trans isomer

Ph3P
Y
Alkenyl-X gives stereo-retained product.
Alkyl-Br + Pt(PEt3)2

1-3. Reductive Elimination
GeneralA
LnM(m+II)

LnM(m) + A-B•Retro reaction of oxidative addition.
•3-membered transition state.

BReactivity : Complex with lower d-orbital energy level shows higher reactivity.
highCo(III), Rh(III) Ni(II), Pd(II) aregood species for reaductive elimination.
Only cis-ligands undergoes reductive elimination.

low
Reactivity (Ligands)
Alkyl (Me < Et < nPr < nBu ) < Aryl, Alkenyl < H
Elimination of alkyl grouprequires strained TS.

Aryl, Alkenyl: -orbital can particilaten the formation of 3-membered TS.
L<LnM

Hydride (H) has spherical symmetry
and form TS without strain,

RM<L

H

Reductive Elimination from Group 10 metal (II) Complex
LR(a) Dissociation path

R'

R-R' + ML
LMRR' (14e) are difficult to generate,
but highly reactive to reductive elimination.

M

cis-L2Pd-(alkyl)2–L +LRLM(b) Direct path
R-R' + ML2

Most Pd complexes

R-R' + ML3

Most Ni complexes

R'L–L +L
L L R
M
R'L

(c) Assosiation path
Ni is easy to form
5 coordinated complexes.

1-4. Insertion and Elimination
CO Insertion and Elimination
OCCOLnM
RLnMROLnMR•R and CO must be cis.
•Reversible process.
•Attack of R– to CO's LUMO.

3

CO does not move and R rearrange to CO group.
CH3OC
COOC
COCH3+LMn
Mn
COCOOCOC
COCO
Mn(I), d6, 18eMn(I), d6, 16e

L COCH
3Mn
COOC
COMn(I), d6, 18e
OCMore -donating, nucleophilic group have large K.
COCOR
R
Ph3P
Ph3P
ClKRh
Rh
PPh3
PPh3
Cl
Cl
Cl
Rh(III), d6, 18e
Rh(III), d6, 16eElectronwithdrawing ligand more strongly coodinate to M.
Espcially, M-H bond is far stronger than M-C bond.
Also CO insertion to M-CO bond cannot proceed.

L = CO or PR3

K>50~173.4±0.2
0.07
<0.05
<0.02

REt, nPr, Bn
PhCH2CH2CH3
pClC6H4CH2
Ph
ClCH2, H

Insertion of Alkene, Alkyne and -Hydride Elimination
B
InsertionA

B

D-Elimination

LnM

R

A
D
LnM

C
R

C

These processes are reversible.
Alkyl complexes are easy to undergo -elimination.

A
B

LnM

InsertionA

B-Elimination

LnM

R

R+PMe3+Co CD
3
CD3Co

Co CD
3H

CD3
D3C

CD3
66

Co(III), d , 18eCo
PMe3–CD3H–CD3Co(III), d6, 18e
Co(I), d8, 18e
Only -hydride eliminated product was observed.

Co(III), d , 16e

Mechanism
Cp*

Cp*

HNb

Cp*

Cp*

HNbR

Cp*

Nb
R

Cp*

Nb(III), d2, 18eR

Nb(III), d2, 16e

Reaction with Pd(II) Complex
OCH3O

CH3CH3O+Ph3P

Pd

PPh3– PPh3Ph3P

Pd

Ph3P

Pd

ClClClPd(II), d8, 16e
Reaction proceeded dissociatively. Cationic (dppe)Pd(Ac)(CH3CN)+ complex shows higher reactivity.

41-5. Cycloaddition
Cycloaddition of Schrock Carbene
Cp

MeCp
Ti
ClCp

DMAPAlMeCp
Ti

Ti

CH2
[2 +2 ]Cp
Ti(IV), d0, 16eTebbe Reagent
Schrock Carbene

Ti(IV), d0, 16e

Cp
Ti(IV), d0, 16e
The same reversible process isthe key for olefin methathesis.

RO

R

R

Cp

H2C

Ti

RO

Cp

R+Cp2Ti=O

R

Ti(IV), d0, 16e

Oxidative Cyclization
Cp

Cp±C2H4Zr

PhZr

Cp

Ph

Cp
2Zr(IV), d , 16e

PhZr

Cp0PhCp

Zr(IV), d0, 16eZr(II), d , 16e

Low valent alkene, alkyne complexes undergo this reaction.

1-6. Reactions at Ligands
Nucleophilic Attack to Metal-Alkene Complexes
Nu–HHNu+•Nucleophilic attack occured on opposite face to metal.
•Nucleophilic attack occured at more substituted carbon.
MLn •Metal with high oxidation state

H
R
M–
2to 1
Pd(II)-alkene complexes have been well studied.
Nu: Alcohols, Amines, Enolates
RM+LnR

Nu–

Reactions of Allyl Ligands
1-Allyl Complexes show nucleophilic reactivity.
Ph2PC6F5Pd+P
Ph2Pd(II), d8, 16eO
OO

Ph2
P+ C6F5PdP
Ph2O–
O

Pd(II), d8, 16e
OPh2P
C6F5PdPPh2OO

Pd(II), d8, 16eO

53-Allyl Complexes show electrophilic reactivity.
(a)

LnM

(b)

LnM

NuLnM

(b)

(c)
Nu–(c)(a)
Example of Path (c)Me2N PhPdN
Me2

Ph +NuLnM

Nu + MLn

Nu: Malonates, Amines

Nu + MLn

Nu: Grignard ReagentsNu

Low valent Pd(0) is unstabilized by -donating N ligand.
PhMe2NPhPdNC(CN)(CH3)2
Me2

NaC(CN)(CH3)2

Hard nucleophiles, MeLi, H–, favor path (c).
Metals which disfavor low valent states, Zr(IV), W(IV), Pt(II), tend to react through path (c).

Reactions of CO Ligands
O

LnM+ CO + Nu–The weaker -backdonation,
the higher reactivity of CO group.

LnM
Nu

PPh3
Cl

PPh3

NuH

Pt CO

Cl

PPh3

PPh3O

Pt

Pt

Cl

PPh3

NuHPt(II), d8, 16e

PPh3baseOH

PPh3ClNuH–H+

PPh3Pt(II), d8, 16eO

Pt
NuPt(II), d8, 16e

NuH = alcohols, amines
Removal of CO by TMANO

O(OC)4Fe

Fe(CO)5–CO2O(H3C)3N+ (CH3)3NO

Fe(0), d8, 18e

Fe(CO)4 N(CH3)3Fe(0), d8, 18e

Fe(0), d8, 18e

2. Homogenious Catalysis
2-1. Isomerization of Olefin
R2NRh(I)+PSRh

PPS
d8, 16eRh
P

NR2

R2N

NR2
R2N

d8, 16e
reductive
elimination

R2N

ligandexchange

Takasago's Menthol Synthesis
Catalytic Cycle
NEt2[((S)-BINAP)Rh+]

PPRh

H
NEt2
96-99% ee

PRh

NR2NR2
d6, 18eP
oxidative
addition
to C-H bond

NR2NR2d8, 16e6

2-2. Hydrogenation
Ph3PRh(PPh3)3ClR

H2RH2ClH

HRh

R

PPh3

Sd , 18e6oxidativeaddition
Ph3P

Cl

Ph3P

Ph3P

ClRh
PPh3Sd8, 16e

Rh
Cl
PPh3d8, 16e

Catalytic Cycle

HHRh

Cl

PPh3
R
d6, 18e

reductiveelimination

Rh catalyzed hydrogenation proceeds
through dihydride mechanismSligandexchange

Insertion

RPh3P
ClR

H

S

Rh

PPh3
S
d6, 18e2-3. Hydroformylation

Co or Ru cat.
CO/H2CHO

CHO+CHOH
L2Rh
COLinear product is more valuable.
Rh-PPh3 system gives good selectivity.
Process using PPh3 as solvent exist.

H2HRh(CO)L2d8, 16e
reductiveeliminationO

CH2CH2CH3H
L2Rh

H

CO
d8, 18ed6, 18eoxidativeaddition

Catalytic Cycle

insertionO

CH2CH2CH3

CH2CH2CH3

L2Rh

L2Rh
CHO
d8, 16einsertion

COd8, 16e

CO

L2Rh

CH2CH2CH3CO

CO
d8, 18e72-4. Hoechst-Wacker Oxidation
H

H

PdCl2 (cat)CuCl2 (cat)H

H

H2O, O2

2 HCl + 1/2 O2

H2O

O
H

2CuCl
O

2CuCl2
H+Pd(II)
Pd(0)Pd(II)

H+H2O
Catalytic Cycle
OH

H

Pd(II)OH

C

Pd(II)H

OH

A

Pd(II)

2 Proposal Pathways to Give ProductB
From C

From AH2OO HHO
Pd(0) +Pd(II)+H

HO+

H3O

Pd(II)

O
Pd(0) +H2O+
H

H3O+Reaction using D2O instead of H2O gave no deuterated aldehyde.
So pathway of non-Pd-catalyzed isomerization from B was denied.

2-5. Carbonylation of Methanol
Rh cat.
HI, CO

CH3OH

CH3COOH

CH3I
CORh
I
COI
6
oxidative d , 18e

CH3OH

CH3I
I
HI

non-metallic
cycle

COI

insertion

addition–Rh

H2O––Organometallic
Cycle

COO
H3C

reductive
elimination

IRhI

2-6. Other Reactions

I

COCH3COd6, 16e–CO
I

CH3COOHRh
I

8d , 16e

I

COCH3COCOI
d6, 18eHeck Reaction, Cross Coupling, Olefin Methathesis etc.
8