6/2/2015insertion and elimination1 insertion and elimination olefin polymerization 1,1-insertion of...
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04/18/23 Insertion and Elimination 1
Insertion and eliminationolefin polymerization
1,1-insertion of CO, isonitriles, SO2, ...
Migratory insertion!
MC
R
O
ML
O
R
MO
R
M
O
R L
04/18/23 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 no CO polymerization.Isonitriles do polymerize!
04/18/23 Insertion and Elimination 3
Insertion van CO en isonitriles
Double CO insertion ?
"Pd"R2NCOCOAr + R2NH2
+ I-2 R2NH + 2 CO + ArI
04/18/23 Insertion and Elimination 4
Insertion van CO and isonitrilesNo double
CO insertion !
subst
nucl attack
red elim
ins
ox addCO
- H+HNR2
- X-CO
L2PdCONR2
COAr
+
L2PdCO
COArL2Pd
X
COAr
CO
L2PdAr
X
- n COArXL2Pd(CO)n
R2NCOCOAr
04/18/23 Insertion and Elimination 5
Insertion van CO and isonitrilesIncrease rate of insertion:
• "Bulky" ligands
• Lewis acidsCoordinate to O,stabilize product
MC
R
O
AlCl3
M
O
R
AlCl3
vs
MCO
RM
O
Rrequires more space than
04/18/23 Insertion and Elimination 6
Insertion van CO and isonitriles
Insertion is not always "real":
Ir OMe Ir OMe
Ir CO OMeCO
Ir COOMe
04/18/23 Insertion and Elimination 7
1,2-insertion of olefins
Standard Cossee mechanism
MR
MR
M
R
MR
04/18/23 Insertion and Elimination 8
1,2-insertion of olefins
Insertion in M-H bonds is nearly always fast and reversible. Hydrides catalyze olefin isomerization.
Regiochemistry corresponds to M+-H-
To shift the equilibrium to the alkyl:– Electron-withdrawing groups at metal– Early transition metals– Alkynes instead of olefins
04/18/23 Insertion and Elimination 9
1,2-insertion of olefins
Metals have a preference for primary alkyls.
But substituted olefins are more stable!
Cp2ZrHClxs
or
or
Cp2ZrCl
+ +
+ little
Most stable alkyl
Most stable olefin
jkjkkj
04/18/23 Insertion and Elimination 10
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)
M M
04/18/23 Insertion and Elimination 11
1,2-insertion of olefins
-agostic interaction facilitates tilting of alkyl and accelerates insertion ("Green-Rooney")
M
04/18/23 Insertion and Elimination 12
1,2-insertion of olefins
Repeated insertion:dimerization, oligomerization, polymerizationM H
M Et
M Bu
M Hx
M H +
+M H
etc
Key factor: kCT / kprop =
» 1: dimerization 1: oligomerization
(always mixtures) « 1: polymerization 0: "living" polymerization
04/18/23 Insertion and Elimination 13
1,2-insertion of olefins
• Dimerization rarely desired
• Oligomers: surfactants, comonomers
• Polymers: plastics, construction materials, foils and films
04/18/23 Insertion and Elimination 14
1,2-insertion of olefinsSelective trimerization is possible but follows
a complicated mechanism
MIV
MIV
MII
MIV
HMIV
MIIMII
redelim
subst coord
coord
ins
-elim
M = Ti
+
04/18/23 Insertion and Elimination 15
CO/olefin copolymerizationM
O P
M
O
P
O
M
O
P
CO
MCO
O P
O
M
O P
O
CO
CO
M = L2Pd, L2Ni
04/18/23 Insertion and Elimination 16
CO/olefin copolymerization
• No double CO insertionuphill
• No double olefin insertionCO binds more strongly, inserts more quickly
• Slow -elimination from alkyl5-membered ring hinders elimination
04/18/23 Insertion and Elimination 18
1,n insertions/additions
Attack on an -polyeneis always at aterminal carbon Usually ,-insertion
A diene can be 2 bound 1,2-insertion
M
R
R
M
MR
MR
04/18/23 Insertion and Elimination 19
1,n insertions/additions
Diene rubbers:
Can be influenced by choice of catalyst.
cis 1,4
trans 1,4
1,2
04/18/23 Insertion and Elimination 20
1,n insertions/additions
Addition to enones:
• RLi, Grignards:usually 1,2
• OrganoCu compoundsoften 1,4
O
R OH
O
R
04/18/23 Insertion and Elimination 21
Less commonelimination reactions
-elimination
Cp2Zr
- Cp2Zr
Zr H
HHtBu
tBuH
04/18/23 Insertion and Elimination 22
Less commonelimination reactions
Other ligand metallation reactions
-
L2Pt L2Pt
-ZrZr
Via -bond metathesisor oxidative addition/reductive elimination
04/18/23 Insertion and Elimination 23
Less commonelimination reactions
-bond metathesisCp*2Lu CH3 + CH4 Cp*2Lu CH3 + CH3H
Lu H
HHH
HHH
"H+" transfer fromalkane to alkyl