PART 2.

ππππ-BONDED ORGANOMETALLICS

1

Figure 1. Binary, Mononuclear Metal Carbonyls

OC

CO

Mn Mn

CO

CO

COOCCO

OC

OC CO

OC CO

Co Co

COCO

OCCO

OC

OC OC

OC

Fe Fe

COCO

OCCO

OC

OC OC

OCCO

FeFe

FeCO

CO

OC

OC

CO

CO

OC CO

OC

COCO

OC

OsOs

OsOC

CO

OC

OC

CO

CO

OCOC

OC

CO

CO

OC

Mn2(CO)10 Fe2(CO)9 Co2(CO)8

Fe3(CO)12Os3(CO)12

CoCo

Co

Co

Ir(CO)3(OC)3Ir

Ir(CO)3

Ir(CO)3

Ir4(CO)12

Co4(CO)12

OC COOC

OC CO

CO

CO

OC

OC

OCCO

CO

Rh

Rh

Rh

Rh

Rh

Rh

OC

CORh= Rh(CO)2

Rh6(CO)16

Figure 2. Binary, Polynuclear Metal Carbonyls

V(CO)6 Cr(CO)6

Mo(CO)6

W(CO)6

Fe(CO)5

Ru(CO)5

Os(CO)5

Ni(CO)4

2

p

s p

s

pσ∗

pπ∗

sσ∗

pπ

pσ

sσ..........

C O

p

s

p

s

pσ∗

pπ∗

sσ∗

pπ

pσ

sσ..

......

..

N N

M C≡Ο:::: M C≡Ο::::

σ-donation from CO

π-backbonding from M

Figure 3. MO Diagram for CO Figure 4. MO Diagram for N2

Figure 5. Bonding of Terminal CO to M

Free Terminal µµµµ2-CO µµµµ3-CO

CO M-CO COM

MCO

M

M

M

ννννco cm-1 2143 1850-2120 1750-1850 1620-1730

Figure 6. Effect on CO Stretching Frequency

3

Mn- C Oδ−σ

π

π

Mn C Oσ

π

π

Mn+ Cδ+ Oσ

π

πanionic neutral cationic

ννννco cm-1

V(CO)6- Cr(CO)6 Mn(CO)6

+

1860 2000 2090

Figure 7. Effect of Charge on Central Metal

Complex vco cm-1

Mo(PF3)3(CO)3 2055, 2090

Mo(PCl3)3(CO)3 1991, 2040

Mo(P{OMe}3)3(CO)3 1888, 1977

Mo(PPh3)3(CO)3 1835, 1934

Mo(MeCN)3(CO)3 1783, 1915

Mo(Py)3(CO)3 1746, 1888

Figure 8. Effect of Ancillary Ligands

4

TiCl4(DME)2 + 6 K[C10H8] + 4 15-Crown-5 + 6 CO ⇒ 2[K(15-crown-5)2]+ [Ti(CO)6]2-

VCl3 + 3Na + 6 CO + diglyme ⇒ [Na(diglyme)2]+[V(CO)6]-

CrCl3 + Al + CO in C6H6 ⇒ Cr(CO)6

WCl6 + 2 AlEt3 + CO in C6H6 ⇒ W(CO)6

2 Mn(OAc)2 + 2 AlEt3 + CO ⇒ Mn2(CO)10

Re2O7 + CO ⇒ Re2(CO)10

Ru(acac)3 + CO + H2 ⇒ Ru3(CO)12

2 CoCO3 + CO + H2 ⇒ Co2(CO)8

Metal salt + reducing agent + CO:

Metal + CO:

Ni + CO ⇒ Ni(CO)4 at atmospheric pressure and room temperature

Fe + CO ⇒ Fe(CO)5 at 100 bar and 150˚C

Figure 9. Synthetic Methods

Na2[Fe(CO)4

RCR'

O

CO

ORC

OH

ORC

X

Fe

C

CO

COOC

OC

OR-

Fe

R

CO

COOC

OC

-RX RC(O)Cl

R'X R'X

O2O2

X2X2

RD

D+ H+

RCHO

RCO2HRCONR'2R'2NH H2O

Fe(CO)5

Na/HgTHF

Figure 10. Collman’s Reagent

5

Rh

MC

C

π∗

M

C

C

σ-donation from C2H4 π-backbonding from M

π

Figure 11. Dewar-Chatt-Duncanson Model for Monoolefin-Metal Bonding

PtCl

Cl

Cl CH2

CH2CF2

CF2CH2

CH2

Pt

Ph3P

Ph3P C(CN)2

C(CN)2

149 pm140 pm137 pm

CH2

CH2

134 pm

Figure 13. Effect on C=C Bond Length

Figure 12. Effect on Geometry

MC

C

H H

H H

M

C

C

HH

HH

weak M→ olefin backbonding strong M→ olefin backbonding

metallocyclopropane

sp2sp3

Example: Example:

6

Ligand

Ψ1 Ψ2 Ψ3 Ψ4

s

pz

dz2

py px

dyz dxz

dxy

Metal

σ π π δ

Figure 14. Metal-Ligand Interactions in Butadiene Complexes

totally a-bonding!

Ψ1

Ψ2

Ψ3

Ψ4

Ψ1

Ψ2

Ψ3

Ψ4

ground state excited state

weak M→ diene backbonding strong M→ diene backbonding

ZrFe

OCCO

OC

e-withdrawing ligands e-donating ligands

metallocyclopentene

sp3

Figure 15. Effect of Backbonding

classify the butadieneligand in these twocompounds!

7

Cl

Cl

+ 2 Fe(CO)5-FeCl2-7 CO

Fe

OCCO

OCCe(IV)

Figure 16. Stabilisation of Cyclobutadiene on Fe(CO)3 Fragment

PtRH2N

Cl

Cl CtBu

CtBu

Figure 17. 2e Alkyne Ligand

124 pm Co(CO)3(OC)3Co

PhCCPh

Figure 18. 4e Alkyne Ligand

146 pm

Figure 19. Bonding in a Fischer Carbene Complex

M :C

OMe

R

carbene acts as L ligand

M C

OMe

R

sp2

M C

OMe

R

π-backbonding from Mσ-donation to M

C

O

R

Me

:

but, competes with:

8

N

C:

N

tBu

tBu

Figure 20. A Stable N-Heterocyclic Carbene (NHC)

N

C:

N

tBu

tBu

N

:C

N

tBu

tBu

Pd

Figure 21. Palladium NHC Complex

Fischer

LnM :C

X

Y

C

X

Y

LnM

C-X

Y

LnM+C+X

Y

LnM-

electrophilic C nucleophilic C

Low oxidation state M, e.g. Cr(0), Fe(0) High oxidation state M, e.g. Ta(V)

X, Y = NR2, OR

Schrock

X, Y = R, H

Ln = CO (π-acceptor) Ln = C5H5, Cl, R (π/σ-donor)

Figure 22. Comparison of Fischer vs Schrock Carbene Complexes

L type ligand X2 type ligand

9

Co

W tBu

tButBu

tBu

W tBu

PMe3

tBu

tBu

PMe3

+ 2 PMe3

Figure 23. Formation of Schrock's "yl-ene-yne" Complex

Metal Halide + Allyl Grignard Reagent:

NiBr2 + 2 C3H5MgBr Ni

Insertion of Dienes into M-H:

Co(CO)4H +

Me

COCOOC

Co

Me

COCOOC

+

syn anti

-CO

HX Elimination from Propene Complex:

PdCl2 + PdCl2base

-HClPdCl Pd Pd

Cl

Cl

dimer.

Nu- or E+ Attack on Coordinated Alkene Ligand:

Ir

MeMe

Ir

CH3

CO

Me

Me

H+/CO

+

Figure 24. Synthetic Routes to Allyl Complexes

-CMe4

tBu Li6+

WCl6

-78˚C

10

syn anti

H1

H2

H3

H1H2

H2

H1

H3

H2H1

MM

H2

H1

H3

MH2

H1

ηηηη3333 ηηηη3333ηηηη1111

Pd

Cl

Pd

Cl

H3

H1H2

@ 25˚C:

345

345

@ 140˚C:

Predict 1H NMR of

Hint: H1 and H2 do notcouple to each other!

Figure 25. Fluxionality in ηηηη3-Allyl Complexes

δ/ppm

δ/ppm

11

a1 e1 e2

s dz2 pz

σσσσ

a1g a2u

ππππ

δδδδ

dyz

dxzpx

py

dx2-y2dxy

e1g e1u

e2g e2g

Figure 26. Bonding in Metallocenes I

12

. .

.. ..

.. ..

.. ... .

. .a1g

a2u

e1g

e1u

e1u*

a2u*

e2g*

a1g*

e2u

e2g

a1g'

e1g* ππππ

σσσσ

δδδδd, a1g, e1g, e2g

s, a1g

p, a2u, e1u

a1g

a2u

e1g

e1u

e2ue2g

Fe

Fe

D5d

Figure 27. MO Diagramfor Ferrocene

Frontier OrbitalOccupancy

Number of UnpairedElectrons

Spin Only MagneticMoment in µµµµΒΒΒΒ

V {e2g}2{a1g}

1 3 3.87

Cr {e2g}3{a1g}

1 2 2.83

Mn {e2g}2{a1g}

1{e1g*}2 5 5.92

Fe {e2g}4{a1g}

2 0 0

Co {e2g}4{a1g}

2{e1g*}1 1 1.73

Ni {e2g}4{a1g}

2{e1g*}2 2 2.83

Figure 28. Stable 1st Row Metallocenes

13

FGNC-PROBLEM CLASS 4

1. Explain why the carbonyl complexes [V(CO)6]-, [Cr(CO)6], and [Mn(CO)6]

+ exhibit

similar patterns of bands in the νCO stretching region of their IR/Raman spectra, but the

frequencies (in cm-1) are highest for [Mn(CO)6]+ and lowest for [V(CO)6]

-.

2. Complete the following reaction sequences:

PhLi ? ?(a) Cr(CO)6 ------------> ?--------------> Cr(CO)5C{OMe}Ph----------> Cr(CO)4I(CPh)

xs LiCH2CMe3

(b) TaCl2(Me3CCH2)3 ----------------------------> ?

-PF3

(c) CoH(PF3)4 + butadiene --------------------> ? + ?

base(d) PdCl2 + propene ----------> ? --------------------> ?

(e) Cr(CO)6 + cyclohepta-1,3,5-triene -------------------> ?

(f)Fe(CO)5 + cyclopentadiene -------------------> ?

? ? AlCl3/CH3COCl(g) Cyclopentadiene ----------> ? -----------> Fe(η-C5H5)2 ----------------------> ?

14

co-condense at –196˚C(h) Ti(a) + benzene ------------------------------> ?

(i) Cr(CO)6 + 1,3,5-trimethylbenzene ----------------> ?

3. Place the following in increasing order of C=C bond length:

C2H4, Pt(PPh3)( C2(CN)4), K[PtCl3(C2H4)]

4. How do Schrock carbene complexes (alkylidenes) differ from Fischer carbene

complexes?

5. Discuss the following observations:

(a) Fe(η-C5H5)2 and Ni(η-C5H5)2 can be oxidised to the corresponding mono-cations, both

of which have one unpaired electron.

(b) The metal to ring distance in Fe(η-C5H5)2+ is longer than in Fe(η-C5H5)2, whereas the

metal to ring distance in Co(η-C5H5)2+ is shorter than in Co(η-C5H5)2.