Insertion and elimination olefin polymerization

1
Insertion and eliminationolefin polymerization

• 1,1-insertion of CO, isonitriles, SO2, ...
• Migratory insertion!

2
Insertion of CO and 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!

3
Insertion of CO and isonitriles

• Double CO insertion ?

4
Insertion of CO and isonitriles

• No doubleCO insertion !

5
Insertion of CO and isonitriles

• Increase rate of insertion
• "Bulky" ligands
• Lewis acids
• Coordinate to O,stabilize product

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Insertion of CO and isonitriles

• Insertion is not always "real"

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1,2-insertion of olefins

• Standard Cossee mechanism

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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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1,2-insertion of olefins

• Metals have a preference for primary alkyls.
• But substituted olefins are more stable!

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1,2-insertion of olefins

• Insertion in M-C bonds is slowerthan in M-H.
• Barrier usually 5-10 kcal/mol higher(factor
  105-1010 in rate!)
• Reason shape of orbitals (s vs. sp3)

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1,2-insertion of olefins

• a-agostic interaction facilitates tilting of
  alkyl and accelerates insertion ("Green-Rooney")

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1,2-insertion of olefins

• Repeated insertiondimerization,
  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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1,2-insertion of olefins

• Dimerization rarely desired
• Oligomers surfactants, comonomers
• Polymers plastics, construction materials, foils
  and films

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1,2-insertion of olefins

• Selective trimerization is possible but follows a
  complicated mechanism

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CO/olefin copolymerization
M L2Pd, L2Ni
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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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Hydroformylation
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1,n insertions/additions

• Attack on an h-polyeneis always at aterminal
  carbon
• Þ Usually a,w-insertion
• A diene can be h2 bound
• Þ 1,2-insertion

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1,n insertions/additions

• Diene rubbers
• Can be influenced by choice of catalyst.

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1,n insertions/additions

• Addition to enones
• RLi, Grignardsusually 1,2
• OrganoCu compoundsoften 1,4

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Less commonelimination reactions

• a-elimination

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Less commonelimination reactions

• Other ligand metallation reactions

Via s-bond metathesisor oxidative
addition/reductive elimination
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Less commonelimination reactions

• s-bond metathesis

"H" transfer from alkane to alkyl
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Less commonelimination reactions

• b-elimination from alkoxides of late transition
  metals is easy