Oxidative addition. An Inorganic Chemistry Topic.

1. Presented By-
Swapnali Borah
M.Sc 4th Semester
Roll No. 17

2. 1. Concerted, or three‐center, oxidative addition mechanism
2. SN2 mechanism
3. Radical mechanisms
4. Ionic Mechanisms
Introduction
Conditions for oxidative addition
Characteristics of oxidative addition
Examples
Mechanisms-
Applications
Conclusion
References

3. IT IS A PROCESS BY WHICH A METAL CENTRE IN A COORDINATIVELY UNSATURATED
COMPLEX INCREASES ITS OXIDATION NUMBER AS WELL AS COORDINATION NUMBER.
Ln M + X Y Ln M
X
Y
16 e- 18 e-
O.S. = + 2
C.N. = +2
THE REVERSE OF THE OXIDATIVE ADDITION IS CALLED REDUCTIVE ELIMINATION.
OXIDATIVE
ADDITION
REDUCTIVE
ELIMINATION

4. • Metal must possess non-bonding electron pair.
• The complex must be co-ordinatively
unsaturated.
• Suitable orbitals should be available.
• The higher oxidation state of the metal should
be energetically accessible and stable.

5. • Two new anionic ligands are added.
• Coordination number increases by two units.
• Oxidation number increases by two units.
• The oxidation state of the metal is low.
• The more electron rich the metal, the more
the addition becomes easier.
• The substrate behaves both as a Lewis acid
and a Lewis base.

6.  Reaction of Vaskas complex with molecular
hydrogen

7. • Oxidative addition without cleavage of the
X-Y bond.

8. X-X
H2, Cl2, Br2, I2
C-C
Ph3C-CPh3, MeC(CN)3
H-X
HCl, HBr, HI, HCN
C-X
CH3I, CCl4, C6H5I
M-X
HgCl2, R3SiCl, Ph3PAuCl
ATOMS SEPARATE ATOMS REMAIN ATTACHED
O2,
SO2,
CF2=CF2
RNCS, RNCO
CS2
RN=C=NR’
Table : Substances that can be added oxidatively.

9. OctahedralOctahedral
OctahedralpyramidalSq
OctahedralTBP
OctahedralplanarSq
planarSqlTetrahedra
planarSqLinear
XL
X
XL
X
XL
X
22
2.2
.
.
.
2
2
2
2
2
2
,2
,
,2
 

 

 








10. MECHANISM OF OXIDATIVE ADDITION
 There are four mechanisms :
o Concerted or three-centered
o SN2
o Radical
o Ionic
1. CONCERTED MECHANISM :
 Follows when X-Y is non-polar.
 Proceeds through two steps-
a. The associative step which involves formation of a Ϭ- complex.
b. Oxidative part of the reaction in which metal electrons are formally
transferred to the σ* orbital of A−B .
16e- ,M(0) 18e- , M(0) 18e-, M(II)
a b

11. 2. SN2 Mechanism
• Often found in addition of polar ligands like methyl,
allyl, benzyl halides.
• Proceed via a polar transition state.
• Accelerated in polar solvents.
16e- , Ir(I) 16e- , Ir(III)
16e- , Ir(III)

12. 3. Radical mechanism
 Two types are there :
1.Non- chain radical mechanism.
• Addition of certain alkyl halides to
proceeds through this mechanism.
2.Radical chain mechanism
• A radical initiator is required to keep the
process going.
PtL3
fast
PtL2
PtL2 + RX
slow
PtXL2 + R
PtXL2 + R
fast
RPtXL2
 33ht 
.
..
Pt(II)
Pt(0)
.

13. Ir(I) Ir(II) Ir(III)

14. A. the one in which the starting metal complex adds to
H prior to the addition of the halide X .
B. the other type, in which the halide anion X− adds to
the starting metal complex first, and then the
addition of proton H+ occurs on the metal complex.
4. IONIC MECHANISM
This mechanism for the oxidative addition reaction is
common to the addition of hydrogen halides
(HX) in its dissociated H+ and X− forms.
There are two pathways-

15.    233343 )()()( 33
PRHPtClPRHPtClHPRPt PRPR
   
     
  222 )()()( ClLcodHIr
fast
LcodIrClClHLcodIr slow
A. When cationic part attach first to the metal centre.
• The metal should be electron efficient .
• Ligands should have Ϭ-donating capacity.
Pt(0) , 18e- Pt(II) , 16e- Pt(II) , 18e-
Tetrahedral Sq. Planar Sq. Planar
B. When attack of anion takes place first .
The metal centre should be electron deficient .
Complexes with ∏-acceptor ligand having +ve
charge on it would follow this pathway .
Ir(I) , 16e- Ir(I) , 18e- Ir(III) , 18e-
Sq. planar TBP Octahedral

16.  An important step in many homogeneous catalytic cycles.
• Hydrogenation of alkenes-Wilkinson catalyst
• Pd catalyzed Cross coupling of Ar-B(OH)2and Ar-X –Suzuki
Coupling
R3P Pd PR3
Br
Pd
Br
Ph3P PPh3
Pd0
Pd2+

17.  Thus, both O. A. and R. E. are important processes in
organometallics and catalytic chemistry of transition metal
complexes.
 O. A. is more prominent in case of metal complexes with
low oxidation state. Reverse case applies in R.E.
 O.A. is accompanied by increase in oxidation number and
coordination number
 Oxidation number, coordination number of the metal
increases in O.A. ,vice versa in R.E.
 In both the processes, stereochemical aspects also holds
importance.

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KRISHNA Prakashan Media Pvt. Ltd.
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Pearson India Education Services Pvt. Ltd.
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Keiter, Okhil K. Medhi, 637-642, 2013, Dorling Kindersley ( India ) Pvt. Ltd.
 Advanced Inorganic Chemistry, 3rd Edition, F. A. Cotton, G. Wilkinson, 772-774,
1972, John Wiley & Sons, Inc.
 Michael S. Driver, John F. Hartwig, Organometallics, vol. 17, Issue 6, 1134-1143,
1998.
 Colin Eaborn, Kalipada Kundu, Alan Pidcock, Journal of Chemical Society, 5, 1223-
1232, 1981.
 https://doi.org/10.1021%2Facs.organomet.5b00565