1. Insertion and elimination olefin polymerization
1,1-insertion of CO, isonitriles, SO2, ...
Migratory insertion!
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Insertion and Elimination

2. Insertion van CO en isonitriles
CO insertion is hardly exothermic.
An additional ligand may be needed to trap the acyl and so force the reaction to completion.
In the absence of extra ligands often fast equilibrium.
CO insertion in M-H, M-CF3, M-COR endothermic Þ no CO polymerization.
Isonitriles do polymerize!
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Insertion and Elimination

3. Insertion van CO en isonitriles
Double CO insertion ?
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Insertion and Elimination

4. Insertion van CO and isonitriles
No double CO insertion !
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Insertion and Elimination

5. Insertion van CO and isonitriles
Increase rate of insertion:
"Bulky" ligands
Lewis acids
Coordinate to O, stabilize product
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Insertion and Elimination

6. Insertion van CO and isonitriles
Insertion is not always "real":
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Insertion and Elimination

7. Insertion and Elimination
1,2-insertion of olefins
Standard Cossee mechanism
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Insertion and Elimination

8. Insertion and Elimination
1,2-insertion of olefins
Insertion in M-H bonds is nearly always fast and reversible.
Þ Hydrides catalyze olefin isomerization.
Regiochemistry corresponds to Md+-Hd-
To shift the equilibrium to the alkyl:
Electron-withdrawing groups at metal
Early transition metals
Alkynes instead of olefins
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Insertion and Elimination

9. Insertion and Elimination
1,2-insertion of olefins
Metals have a preference for primary alkyls.
But substituted olefins are more stable!
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Insertion and Elimination

10. Insertion and Elimination
1,2-insertion of olefins
Insertion in M-C bonds is slower than in M-H.
Barrier usually 5-10 kcal/mol higher (factor in rate!)
Reason: shape of orbitals (s vs. sp3)
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Insertion and Elimination

11. Insertion and Elimination
1,2-insertion of olefins
a-agostic interaction facilitates tilting of alkyl and accelerates insertion ("Green-Rooney")
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Insertion and Elimination

12. Insertion and Elimination
1,2-insertion of olefins
Repeated insertion: dimerization, oligomerization, polymerization
Key factor: kCT / kprop = k
k » 1: dimerization
k » 1: oligomerization (always mixtures)
k « 1: polymerization
k » 0: "living" polymerization
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Insertion and Elimination

13. Insertion and Elimination
1,2-insertion of olefins
Dimerization rarely desired
Oligomers: surfactants, comonomers
Polymers: plastics, construction materials, foils and films
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Insertion and Elimination

14. Insertion and Elimination
1,2-insertion of olefins
Selective trimerization is possible but follows a complicated mechanism
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Insertion and Elimination

15. CO/olefin copolymerization
M = L2Pd, L2Ni
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Insertion and Elimination

16. CO/olefin copolymerization
No double CO insertion
uphill
No double olefin insertion
CO binds more strongly, inserts more quickly
Slow b-elimination from alkyl
5-membered ring hinders elimination
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Insertion and Elimination

17. Insertion and Elimination
Hydroformylation
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Insertion and Elimination

18. 1,n insertions/additions
Attack on an h-polyene is always at a terminal carbon
Þ Usually a,w-insertion
A diene can be h2 bound
Þ 1,2-insertion
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Insertion and Elimination

19. 1,n insertions/additions
Diene rubbers:
Can be influenced by choice of catalyst.
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Insertion and Elimination

20. 1,n insertions/additions
Addition to enones:
RLi, Grignards: usually 1,2
OrganoCu compounds often 1,4
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Insertion and Elimination

21. Less common elimination reactions
a-elimination
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Insertion and Elimination

22. Less common elimination reactions
Other ligand metallation reactions
Via s-bond metathesis or oxidative addition/ reductive elimination
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Insertion and Elimination

23. Less common elimination reactions
s-bond metathesis
"H+" transfer from
alkane to alkyl
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Insertion and Elimination

24. Less common elimination reactions
b-elimination from alkoxides of late transition metals is easy
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Insertion and Elimination