Oxidative addition

Oxidative addition. An Inorganic Chemistry Topic.

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

2. CONTENTS 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 . INTRODUCTION THE REVERSE OF THE OXIDATIVE ADDITION IS CALLED REDUCTIVE ELIMINATION. OXIDATIVE ADDITION REDUCTIVE ELIMINATION

4. Conditions for Oxidative Addition 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. CHARACTERISTICS OF OXIDATIVE ADDITION

6. EXAMPLE OF OXIDATIVE ADDITION Reaction of Vaskas complex with molecular hydrogen

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

8. X-X H 2 , Cl 2 , Br 2 , I 2 C-C Ph 3 C-CPh 3 , MeC (CN) 3 H-X HCl , HBr , HI, HCN C-X CH 3 I, CCl 4 , C 6 H 5 I M-X HgCl 2 , R 3 SiCl, Ph 3 PAuCl ATOMS SEPARATE ATOMS REMAIN ATTACHED O 2 , SO 2 , CF 2 =CF 2 RNCS, RNCO CS 2 RN=C=NR’ Table : Substances that can be added oxidatively.

9. CHANGE IN CO-ORDINATION GEOMETRY ON OXIDATIVE ADDITION

10. Mechanism of Oxidative Addition There are four mechanisms : Concerted or three-centered SN2 Radical 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 Mechanis m 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 t he process going. . . . Pt(II) Pt(0) .

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

14. 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. 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 APPLICATIONS

17. CONCLUSIONS 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 a ccompanied 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.

18. References Advanced Inorganic Chemistry,13 th Edition, Vol ||, Gurdeep Raj, 837-844, 2012, KRISHNA Prakashan Media Pvt. Ltd. Inorganic Chemistry, 3 rd Edition,Gary L. Miessler , Donald A. Tarr , 534-536, 2015, Pearson India Education Services Pvt. Ltd. Inorganic Chemistry, 4 th Edition, James E. Huheey , Ellen A. Keiter , Richard L. Keiter , Okhil K. Medhi , 637-642, 2013, Dorling Kindersley ( India ) Pvt. Ltd. Advanced Inorganic Chemistry, 3 rd 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

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