Oxidative addition and CO insertion reaction.

1. Oxidative addition and CO insertion reaction. 201450720 지 슬기

2. contents • Oxidative addition • Mechanisms of oxidative addition • Type of oxidative addition. • CO insertion reaction. • Two type of insertion reaction. • Mechanisms of CO insertion.

3. Oxidative addition reaction • Oxidative addition • Reverse reaction of reductive elimination. • A process that increases both the oxidation state and coordination number of a metal centre. • often a step in catalytic cycles, in conjunction with its reverse reaction, reductive elimination. X LnM + X-Y LnM oxidative addition reductive elimination Y

4. Type of oxidative addition

5. Three center Cis-addition (Concerted pathway) a b 16e- 18e- a : formation of σ complex b : metal electrons are formally transferred to the σ* orbital of A-B

6. Three center Cis-addition (Concerted pathway) • example d8IrCl(CO)(PPh3)2 d8IrCl(H2)(CO)(PPh3)2

7. SN2 Mechanism(non-concerted) • In the SN2 pathway, adopted for polarized A-B substrates such as alkyl halides, the metal electron pair of LnM directly attacks the A-B σ* orbital by an in-line attack at the least electronegative atom formally to give LnM2+ , A- and B- fragments.

8. SN2 Mechanism(non-concerted) • Often found in the addition of methyl, allyl, acyl, and benzyl halides.

9. Ionic mechanism • Hydrogen halides(e.g. HCl, HBr, HI) are often largely dissociated in solution, and the anion and proton tend to add to metal complexes in separate steps. H+ +Cl- HCl

10. Ionic mechanism • example

11. CO insertion reaction

12. Insertion Reactions • An insertion reaction is a chemical reaction where one chemical entity (a molecule or molecular fragment) interposes itself into an existing bond of typically a second chemical entity.

13. Insertion Reactions • There are two main types of insertion. • 1,1 insertion in which the metal and the X ligand end up bound to the same(1,1) atom • 1,2 insertion in which the metal and the X ligand end up bound to adjacent (1,2) atoms of an L-type ligand.

14. CO Insertion Reactions • Perhaps the most well-studied insertion reaction is carbonyl insertion, which involves the reaction of CO with an alkyl complex to give an acyl product. • H3C-Mn(CO)5 + CO CH3C-Mn(CO)5 O

15. CO Insertion Reactions • Mechanism 1 : CO Insertion • direct insertion of CO into metal-carbon bond. • Mechanism 2 : CO Migration • migration of CO to give intramolecular CO insertion. This would alsogive a 5-coordinate intermediate with a vacant site available for an incoming CO. • Mechanism 3 : Alkyl Migration • the alkyl group would migrate, rather than the CO, and attach itself to a CO cis to the alkyl. This would also give a 5-coordinate intermediate with a vacant site available for an incoming CO.

16. CO insertion reaction

17. CO Insertion Reactions • Experimental evidence • Reaction of CH2Mn(CO)5 with 13CO gives a product with the labeled CO in carbonyl ligands only ; none is found in the acyl position. • the reverse reaction • The reverse reaction, when carried out with 13C in a carbonyl ligandcis to the acyl group, gives a product that has a 2:1 ratio of cis to trans product. O CH3C-Mn(CO)5 H3C-Mn(CO)5 + CO

18. CO Insertion Reactions

19. CO Insertion Reactions

20. CO Insertion Reactions

21. Reference • 이공학을 위한 무기화학 강의 p715~724 • Wikipedia, google • Inorganic chemistry – third Edition, Gary L. Miessler ∙ Donald A. Tarr

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