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 17

Hydroformylation

HM M

HM

COCO

M

M

O

MH2

O

M

H

O

HH

O

H2

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

04/18/23 Insertion and Elimination 24

Less commonelimination reactions

-elimination from alkoxides of late transition metals is easy

MO CH3 M

H+ CH2O