organologam lengkap

8/10/2019 organologam lengkap

1/70

Outl ine

1. Review on coordination chemistry2. The 18-electron rule

3. Limitations of 18-electron rule

4. Oxidation number

5. Coordination number and geometry

6. Effect of complexation

7. Differences between metals

Chapter 1. General properties of organometallic

complexes

1. The Organometallic Chemistry of the Transition Metals, Robert H. Crabtree,

3rd Edition, 2001, Chapter 1-2.

2. Organotransition Metal Chemistry, Akio Yamamoto, 1986. Chapter 1-4.

3. Organometallic Chemistry, G. O. Spessard, G. L. Miessler, Prentice-Hall:

New Jersey, 1997, Chapter 13.

References


2/70

1. Review on coordination chemistry

Complexesor coordination compoundsare compounds composed

of a metal and ligandswhich donate electrons to the metal, e.g.

H3N: Co :NH3

H3N:

:NH3H3N Co NH3

H3N

NH3

NH3

NH3

..

..

3+

or

3+NH3

NH3

Ligands: a molecule or ion that has at least one electron pair that can be

donated.

The electron pair can be: lone pair, p-bonding electron pair, or

s-bonding electron pair.


3/70

M M M

H H

M

H SiR 3

M

lone pairs, e.g.

pbonding e- pairs, e.g.

sbonding e- pairs, e.g.

H3N: H3N: M H2O: H2O: M.. ..

Classi f ic at ion of l igands

A). Based on nature of the donating electron pairs, ligands may be

classified as Lone pair donor, p-bonding electron pair donors, s-bonding

electron pair donors.


4/70

1) Lone pair donors

M L

NH2-CH2-CH2-NH2(en).. ..

R-O-..

..: L : :-

In terms of bonding:

..

L

..

L

filledempty

Lor

H3N: :PR3:CO

M

Cl

M M

Note:

Ligands that donate

electron pairs to form M-L

sbond are also called s

donors.

MO description of Metal-Ligand interactions

L ligand

M

M L ligand

M L ligand

Bonding

Antibonding


5/70

e.g. OR-

R-O..

.. :- M+(a)

R-O..

.. M

R-O

-:

M+(b)

MR-O

M

M M

filled

M

empty

orOR- OR- OR

-

OR-

(a)

Note: although ligands

such as OR-can form

pbond with a metal,

we usually don't

indicate suchinteraction in writing

the structures.

Ligands that donate electrons to metal to form pbond are called donor

How manyp

bonds can an OR form with a transition metal ion?

M ORM OR

M OR

Some lone pair donor ligands may have orbitals to form

M-L pbonds. ===> pdonor, pacceptor.


6/70

:C O: C O: C O:

C O: C O:

+(a)

+

(b)

empty

M M

M

M

accept e-to form pbond (dpppback bonding)

CO is not only a sdonor, but also a pacceptor.

How many pbonds can a CO form with a transition metal ion?

Ligands that accepting electrons from metal to form p bond are calledacceptor.


7/70

:C O: C O: C O:

C O: C O:

+(a)

+

empty

M M

M M

C O:+

empty

M C O:M

C OM C OM C OM

Can CO function as ap

donor?

TWO


8/70

Types of lone pair donor ligands

strongpacceptor

weakpbonding

strongpdonor

lone pairdonor

CO, PF3 NH3, H-

CH3-

Cl-, OR-

s

p


9/70

MoOC

OC CO

CH3

2.38 1.99 a)

b) IR, (CO)

:C O

2149 cm-1

C OH3B

2178 cm-1

OC Cr

CO

CO

CO

COOC

2000 cm-1

Evidences for dp

-pp

interactions.

* Take M-CO complexes as an example forp

accepter

Explanation?:C O :C OM C OM

C OM C OM

C OM C OM

-+

1s

1p

3s

2p

4s

2s

C O

2p

3s

1p

CC 2s

C O

C O

(anti-bonding)


10/70

*Take M-OR complexes as an example forp

donor.

Mo Mo

O O

O

O

OO OO t-But-But-But-Bu

120o O

Nb

O

Tp

Tp

Tp = trypticyl

180o

In H2O, O atom has sp3

hybridization, leading to the A-O-B anglebeing about 104.5. However, in the above two complexes the angles

are 120and 180, respectively. Why ?


11/70

2). p-bonding electron pair donors

C O

M

H2C CH2

M

HC CH

M M M

How can these ligands interact with M ?

Take CH2=CH2as an example.

M

1. e - from (C2H4) --->s(M)

M

2. e - from d(M) --->p

(C2H4)

HH

H H

C

C

p

C

C

p

C

C

C

C

HH

H H

M

Is CH2=CH2a pdonor or a pacceptor?


12/70

Hapticity of ligands:

A ligand may have more than one way to bond to a metal center, e.g.

M M

or

M

CHCH2

CH2

H

H

HH

H

(Cp)

H

H

HH

H

M H

H

HH

H

M

M

In describing the number of atoms (n) attached to a metal, a short

hand hnis used. e.g.

M

(h1-C3H5)M

MH

H M

CH2

CH2

(h-H2)M (h-C2H4)M

MAg+ M

(h-C6H6)M (h-C6H6)Ag

+ (h-C6H6)M


13/70

O

CH3

Fe(CO)3

Ru

Fe(CO)3

MeO +

Exercise. Give the hapticity of ligands in following complex


14/70


15/70

3).s

-bonding electron pair donors

Relatively fewer stable complexes are known.

Typical examples:

MH

Hh-H2 OC W

OC

COPR3

PR3

H

H

h-H-SiR3 MH

SiR3Mn

OCOC

H

R3Si

agostic C-H Me2P Ti

Me2P

CH2Cl

Cl

MH

C Cl

CH2Hor M

H

C


16/70

How can these ligands interact with M? Take H2as an example.

M

H

H

H

H

M

s-bonding p-bonding

Further Notes:

* Relative basicity of electron pairs:

lone pairs > pbonding electron pairs > sbonding electron pairs

* Therefore usual order of binding ability:

lone pair donor > pbonding electron pair donor > sbonding electron pair donor.

Consequence:

MH

HM

CH2

CH2

M PR3

CH2

CH2

CH2

CH

H

H

:PR3

Is H2a pdonor or a pacceptor?


17/70


18/70

B) based on the nature of bonding interaction, ligands may be

classified as soft or hard.

Hard ligands: have low polarizability, especially those containing

period 2 donor atoms N, O, F, e.g. O2H, NH3, F-

Soft ligands: have high polarizability, they include:

a). Those with period three or subsequent donor atoms,

e.g.Cl, Br, S, P.

b). p-acceptors, e.g.CO, CS (carbon sulfide), H2, CN- (cyanide)

c). Those containing p-electrons, e.g.

C C C C


19/70

Importance of the concepts of soft and hard ligands:

* Hard ligands tend to form stable complexes with hard metal ions,

(usually those at high oxidation state, e.g. Al3+, Fe3+, Cu2+, Ti4+, Pt(IV)).

* Soft ligands tend to form stable complexes with soft metal ions,

(usually those at low oxidation state, e.g. Mn(I), Co(I), Fe(II), Pt(II),

Pt(0) .......)

Examples:

AlF63-, Ti(OR)4are very stable complexes, but Pt(0)--F, Pt(0)--OR,

W(0)--F are very rare.

Cl Pt

Cl

Cl

-

stable

Pt(IV)

very rare

(Olefins are soft

base; Pt(II) is soft

but Pt(IV) is hard)


20/70

Exercise. explain the following facts based on the concept of Soft-Hard

Acid-Base.

1) W(CO)6

is air stable, but W(NH3

)6

has never been observed.

2).

3). Low oxidation state complexes (most organometallic compounds) are

often air-sensitive, but are rarely water sensitive.

NH2

(NH3)5OsII

2+

- e- NH2

(NH3)5OsIII

3+

NH2(NH3)5OsIII

3+

slow


21/70


22/70

Further notes on ligands

Chelation: Ligand attached through more than one atom usually separated

by one or more atoms. Chelating ligands are sometimes classified as beingbidentate(2 points of attachment), tridentate(three points of attachment), or

tetradentate(4 points of attachment).

Kappa convention (): The kappa convention is sometimes used toindicate the coordinating atoms of a polydentate ligand.


23/70

2. The 18 electron rule

1)Thermodynamically stable transition metal organometallic

compounds are formed when the sum of the metal d electrons plus

the electrons supplied by the ligands equals 18.

In this way, the metal formally attains the electronic

configuration of the next noble gas.

Ni

CO

COOC

OCFe CO

OC

OC

CO

CO

Cr COOC

OC

CO

CO

CO

The 18 electron rule = 18 VE rule = inert gas rule = effective

atomic number rule (EAN rule). e.g.

Saturated complexes: 18 VE complexes

Unsaturated complexes:


24/70

2) Ways to count valence electrons (VE)

# VE = valence e-of M (or Mn+) + e-from ligands

Two Models: covalent modeland ionic model

Covalent model: Both M and L are considered as neutral

# VE = valence e-of M + e-from ligands + charge

e.g.

Fe Cr

H

CO

COCO

OC

OC

2 2 x 5e

Fe 8e

18e

5 CO 5 x2e

H 1e

Cr 6e1- 1e

18e

C5H5

For TM, valence e-of M = group number


25/70

For TM, valence e-of M = group number.

e.g. Fe, 8; Pt, 10


26/70

Ionic model: Metal complexes are formed from Mn++ L + X-

# VE = valence e- of Mn++ e- from ligands

Fe Cr

H

CO

CO

CO

OCOC

2 2 x 6e

Fe2+ 6e

18e

5 CO 5 x 2e

H- 2e

Cr 6e

18e

C5H5-


27/70


28/70

Rh

Cl

Rh

Cl

Rh

Cl

Rh

Cl

OCH3

Fe(CO)3 +

OCH3

Fe(CO)3


29/70


30/70

Fe

OCOC

Mn

COOC

OC

CO

COW


31/70

Rh Rh

OC

CO

(CO)3(PPh3)Fe Ir(CO)2(PPh3)

Ph2P

Co CoN

N

O

O


32/70

Do the following complexes follow the 18e rule?

ReH7(PPh3)2

-

Cr

CO

COCO

H

OC

OCCr

CO

CO

CO

CO

OCRh

H

H

H

+


33/70

R3P Ru

H

H

H

R3P

PR3

B H

H

R3P Ru

H

H

H

R3P

PR3

B NMe3

H

Additional exercise


34/70

Additional exercise

Ir

N

COOC

Ir

OC CO

BPh3

Ir

OC CO

PPh3


35/70


36/70

U

U: 7s25f36d1

2x8+6 = 22e

Lu Me

Lu: 6s24f146d1

2x5+1+17 = 28e

2).F-block metals do not follow 18e rule. e.g.

Why? because electrons can go to (n-2)f orbitals)


37/70

3).Transition metal complexes ===> three classes

Class number of valence electrons 18e rule

I ....16, 17, 18, 19, 20 not obey

II ....16, 17, 18 not obey

III 18 obey


38/70


39/70

Class II: 4d and 5d metals with weak-field ligands

Class II n(VE) 18n(d) n(VE)

ZrF62- 0 12

WCl6 0 12

WCl6

- 1 13

WCl62- 2 14

TcF62- 3 15

OsCl62- 4 16

PtF6 4 16

PtF6- 5 17

PtF62- 6 18

PtCl42- 8 16

Metals in relativelyHigh oxidation state


40/70

Class III: Complexes with pgood acceptors

Class III n(VE) = 18

n(d) n(VE)

V(CO)6

- 6 18

CpMn(CO)3 7 18

Fe(CN)64- 6 18

Fe(CO)42- 10 18


41/70

Explanation:

L M L

L

L

L

L

Take Oh as an example

MO levels in the absence of pacceptors.

* If is small, eg* can be

occupied.( < pairing energy)

===>

eg* (antibonding): 0 - 4e

t2g(nonbonding): 06e

a1g

, t1u

, eg(bonding): 12e

Total e-:

Minimum # of e-:

Maximum # of e-:

3d metal complexes with weak field ligands e.g.H2O, NH3and

Cl-belong to this class (class I).

metal

orbitals

(n-1)d

ns

np

Ligand

orbitals

(a1g+eg+t1u)

(a1g+eg+t1u)

t1u*

a1g*

eg*

t2g

D


42/70

MO levels in the absence of pacceptors.

* If is large, eg* can be occupied.

( > pairing energy)

===>

eg* (antibonding): 0 e

t2g(nonbonding): 06e

a1g, t1u, eg(bonding): 12e

Total e-:

Minimum # of e-:

Maximum # of e-:

Complexes of 4d and 5d metals in high oxidation state belong to

this class (class II).

metal

orbitals

(n-1)d

ns

np

Ligandorbitals

(a1g+eg+t1u)

(a1g+eg+t1u)

t1u*

a1g*

eg*

t2g

D


43/70


44/70


45/70

d0metals:The high-valent d0complexes often have lower

electron counts than 18.

Complexes with bulky ligands:Sterically demanding

ligands will often result in lower than expected electron

counts.


46/70

> 18 electron complexes: Complexes with formally 19 or 20

electrons are known, but they are usually unstable, or

adopt alternate configurations.


47/70

The 18 Electron Rule Is Empirically Justified

The rule is

particularly useful for

Groups 6-8

16 e-Compounds 14 e-Compounds


48/70

The oxidation stateof a metal in a complex is simply the charge thatthe metal would have on the ionic model.

4. Oxidation number of metals and d electron count

e.g.What is the oxidation number of metals in the following complexes?

Fe

H

PR3

PR3

R3PHOs

PPh3

PPh3

ClCl

OCOCWMe6 H

H

d electron count: # of d electrons in the valence shell

= group # - oxidation state.


49/70


50/70

Consider complexes W(CO)6and WH6(PMe3)3.

Which one would you expect to have a higher positive charge on W?

b) charge density and formal oxidation states

There is no strict correlation between charge density and

formal oxidation states!Oxidation states in organometallic complexes

are merely formalisms that may bear little resemblance to the actual positivecharge on the metal.

Another example

Any Uses of formal oxidation states?


51/70

Oxidat ion number usual ly can no t be higher than

group member!

==> predict if a compound/intermediate is possible

==> Help to formulate the structure of a compound.

e.g.

(1) Are the following species possible?WMe6 TiMe6 VH7(PMe3)2

(2) WH6(PMe3)3+ HBF4------> [WH7(PMe3)3] BF4Which of the following is unlikely the structure for [WH7(PMe3)3]

+?

W

H H+

H

H

H PP

P

H

H

W

H H+

H

H

H PP

P

H

H

W

H H+

H

H

H PP

P

H

H

(a) (b) (c)


52/70

Co

Cl

NH3

NH3

Cl

H3N

H3N ReH92-

six-coordinated 9-coordinated

5. Coordination number (C.N.) and geometry

a) It is easy to define C.N. for complexes with lone pair donors.

* Monodentate ligand L :

C.N. = # of L present = # of atoms bound to metal

= # of electron pairs involved in M-L sbonds.

e.g.

P l d t t li d


53/70

Polydentate ligands:

C.N. = # of atoms bound to metal

= # of electron pairs involved in M-L sbonds.

# of L present

Co

Cl

CH3

PPh2

Ph2P

Ir

Ph2P

Cl

PPh3Ph3P

H

4-coordinated 6-coordinated

b)For Organometallic compounds, it is difficult to define C.N. e.g.


54/70

Fe Fe

OC COCO

# of L

Fe Fe

OC

CO

CO

# of M-L

FeFe

OCCO

CO

# of e pairs in M-L bond

C.N. = 1

C.N. = 5

C.N. = 3

C.N. = 1

C.N. = 4

C.N. = 2

2 + 3

2

2

+ 3

+ 3

Convention used in this course.

We normally adopt the e- pairs in M-L bonds as # of C. N..


55/70


56/70


57/70

Further notes on coordination numbers:

a).For TM, C.N. 9 , why?

TM has 9 valence orbitals ((n-1)d, ns, np).

b).dn C.N. and geometry

dn

C.N. geometrical structured6 6 prefer octahedral

d8 4 prefer square planar

d0, and d10 4 prefer tetrahedral

c).Each C.N. is associated with one or more geometries.


58/70


59/70

5 Trigonalbipyramidal M

Fe(CO)5

squarepyramidal

M Co(CNPh)52+

6 Octahedron M Mo(CO)6

trigonalprism M

WMe6

(benzonitrile)

d8,,d6

d6,,d7

d6,,d3

d0

6. Effect of complexation


60/70

M-L:

Complexation of L on M may cause:

* the change of electron density distribution on L

* new reactivity of L: unreactive ==> reactive

Examples:

a. Change the electron density on L. donation will reduce electron-density of L.

-accepting will increase electron-density of L.

H2C CH2

Fe

OCOC Fe

OCOC

R

N. R.+ Nu-

but,

+ + R-

Complexation reduce electron-density of olefin

Another example,


61/70

Mn

OC COCO Mn

OC COCO

H

H

H

H

HH

H

H H

H

HH

H

H

E

E

H

HH

H

H

+

+E+ - H

+

Nu-

N. R.

E+

N. R.

but, NaBH4

(H-)

Complexation reduces the e- density on C6H6.

Reactivity towards Nu-: increase

Reactivity towards E+: decrease

Change the electron density distribution on L


62/70

g y

M :N N:

s-donation

:N N: :C O:

= 0 = 0

unreactive

M C OM N NUpon complexation

N N:

M :C O:

C O:

p- backdonation

C ON N

M C OM N N

overallM C OM N N

+ +

Nu- E+

Nu- E+

M M

MM

(e-to on both atom)

(e-to mainly C atom)++

-- - -



63/70


1) Electronegativity differences:

Sc Ti V Cr Mn Fe Co Ni Cu

1.3 1.5 1.6 1.6 1.6 1.8 1.9 1.9 1.9

Y Zr Nb Mo Tc Ru Rh Pd Ag

1.2 1.3 1.6 2.1 1.9 2.2 2.3 2.2 1.9

La Hf Ta W Re Os Ir Pt Au

1.1 1.3 1.5 2.3 1.9 2.2 2.2 2.3 2.5

Moving from left to right, the electronegativity of the elements increases

substantially.


64/70

2). Trend in the stability of high oxidation states.

From left to right decreaseFrom top to bottom increase

e.g. Ti(II) unstable Fe(II) stable

Ti(IV) stable Fe(VIII) not exist

Hf(IV) very stable Os(VIII) stable

Stability of high oxidation states

Early transition metals are electropositive, so they readily lose all their

electrons to give d0

centers (e.g. Zr(IV), Ta(V)). Low-valent early transitionmetals, such as Ti(II) and Ta(III), are easily oxidized.

Late transition metals are more electronegative, thus they prefer lower

oxidation states (i.e., Rh(I) compared to Rh(III)).


65/70

Q ti 2 H ld l i th f ll i t d i th


66/70

Question 2. How would you explain the following trend in theIR dada of (C-O) (in cm-1)?

a). V(CO)6 Fe(CO)5 CO [Ag(CO)]+

1976 2023 2057 2204

b) Cr(CO)6 2000W(CO)6 1998


67/70

Effects of changing net ionic charge, ligands, and metal on the pbasicity of a metal

carbonyl, as measured by (CO) values (cm-1) of the highest frequency band in the IR

spectrum

Changing Metal

V(CO)6

1976

Cr(CO)6

2000

Mn2(CO)10

2000

Fe(CO)5

2023

Co2(CO)8

2044

Ni(CO)4

2057

Changing Net Ionic Charge in an Isoelectronic Series

[Ti(CO)6]2-

1747

[V(CO)6]-

1860

Cr(CO)6

2000

[Mn(CO)6]+

2090

[Fe(CO)6]2+

2204

Replacing p-Acceptor CO groups by Non-p-Acceptor Amines

[Mn(CO)6]+

2090

[(MeNH2)Mn(CO)5]+

2043

[(en)Mn(CO)4]+

2000

[(tren)Mn(CO)3]+

1960

Question 3. Compounds of the formula MH4P3(M = Fe, Ru and Os, P = PR3)

k t h th f ll i t t


68/70

M

H

H

H

H

M

2. e- from d(M) --->s (H2)1. e - from (H2) --->s(M)

H

HM

s

(H2)s*(H2)

Bonding picture of M(H2)

are known to have the following structure.

P Fe H

P

P

H

H H

P Ru H

P

P

H

H H

P Os

H

P

P

H

H H

why not

P Os HP

P

H

H H

?


69/70


70/70

butadiene cyclooctadiene (COT) cyclooctatetraene (COD) cyclopentadienyl

anion

Date post:	02-Jun-2018
Category:	Documents
Upload:	ikalailatul
View:	249 times
Download:	0 times

organologam lengkap

Documents