Olefin Metathesisand Related Chemistry

Chapter 15.2

2005 Nobel prize in chemistry

Yves ChauvinInstitut Français du Pétrole Rueil-Malmaison, France

Robert GrubbsCalifornia Institute of Technology

(Caltech) Pasadena, CA, USA

Richard SchrockMassachusetts Institute

of Technology (MIT) Cambridge, MA, USA

http://nobelprize.org/chemistry/laureates/2005/index.html

"for the development of the metathesis method in organic synthesis"

Outline Olefin metathesis

Mechanism Reaction overview

ROMP RCM

Grubbs catalysts Stereochemistry Catalyst decomposition

Alkyne metathesis Reactions related to olefin metathesis

M=C complexes: comparison

Property Fischer-type

(carbene)

Schrock-type

(alkylidene)

Nature of carbene C

Typical R groups

Typical metal

Typical ligands also attached to the metal

Electrophilic

donor (e.g. OR)

Mo(0), Fe(O), Cr(0)

Good acceptor (e.g. CO)

Nucleophilic

Alkyl, H

Ti(IV), Ta(V), W(VI)

Good or donor (Cl, Cp, Alkyl)

C

R

R

M C

R

R

M

Fischer carbene Schrock carbene

(OC)5WOR

R

W(0), 18e

Cp2(Me)TaH

H

Ta(V), 18e

Olefin metathesis

Reference: Chem. & Eng. News 2002, Dec 23, 34-38http://nobelprize.org/nobel_prizes/chemistry/laureates/2005/animation.html

Mechanism:

Such cycloaddition reactions between two alkenes to give cyclobutanes are symmetry forbidden and occur only photochemically. However, the presence of d-orbitals on the metal alkylidene fragment breaks this symmetry and the reaction is quite facile.

Normally, the products are statistical, unless the reaction can be driven in some way or the two alkenes have very different reactivities.

R1

R1

R1

R1

R2

R2

R2

R2

+catalyst R2

R2

R1

R1

2

LnMR

R'R'

LnMR

R'R'

MLnR

R'R'

R1

R1

+catalyst R1

R1

R1

R1

2 C2H4

Timeline

Titanium

Tungsten

Molybdenum

Ruthenium

AcidsAlcohols, water

AldehydesKetones

Esters, amidesOlef ins

AcidsAlcohols, water

AldehydesKetonesOlef ins

Esters, amides

AcidsAlcohols, water

AldehydesOlef insKetones

Esters, amides

Olef insAcids

Alcohols, waterAldehydesKetones

Esters, amides

1950

1960

1970

1980

1990

2000

discovery of olef in metathesis

RuCl3 performs ROMP

Chauvin proposes metal alkylidene

-based mechanismevidence for Chauvin's

mechanism found

single-componentcatalysts developed

synthesis of Mo-alkylidene

synthesis of Ru-alkylidene(Cy3P)2Cl2Ru=CHPhmechanism

of (Cy3P)2Cl2Ru=CHPh investigated mono(NHC) Ru

catalysts developed

Reaction overview

R1 R2

+R2

R1

+cross metathesisCM

+ring-closing metathesisRCM

+ring-opening metathesisROM

ring-opening metathesis polymeryzation

ROMPn

+ n

acyclic diene metathesis polymeryzation

ADMET

Large-scale applications of OM PHILIPS process (ARCO, Texas):

SHOP process (Shell): C8 and C16 internal olefins are metathesized in the course of a multi-step

process (ethylene oligomerization, isomerization, metathesis, hydroformylation) leading to C11 – C15 primary alcohols (detergents).

Neohexene (musk scent for perfume industry) synthesis:

+ +

+

Mechanism: pair-wise vs. non pair-wise

M

R1

R1

R1

R1

R2

R2

R2

R2

+R2

R2

R1

R1

2

LnMR

R'R'

LnMR

R'R'

MLnR

R'R'

MM

R1HC

R1HC CHR2

CHR2

R1HC CHR1

R2HC CHR2or

Pair-wise mechanism

Non pair-wise mechanism

+Me

Me+

n-Pr

n-Pr

+

n-Pr

n-PrC16

+

n-Pr

MeC14

Me

MeC12

catalyst

Mechanism: sticky olefin

A system in which the metathesis products do not themselves metathesize is needed such that the initial products are those detected.

The results of this reverse double cross experiment showed a 1:2:1 mixture of d0, d2, and d4 isotopomers of the resulting ethylene.

CH2

CH2

CD2

CD2

+catalyst

+

H2C CH2

1+

H2C CD2

2+

D2C CD2

1

Schrock catalysts: history

Reference: Schrock, R. R. J. Mol. Cat. A: Chem. 2004, 213, 21

Ta

Cl

Cl

tButBu

tBu

Zn

tBu

2Ta

tButBu

tButBu

tBuHHH

HTa

tButButBu

tBu

the f irst example of a stable M=CHR complex

TaR3P

Cl Cl

ClPR3

tBu

WtBuO

tBuO OtBu

OtBu

O

WR3P

Cl PR3

O

Cl

TatBuO

tBuO OtBu

OtBu

Cl

++

the f irst example of a W=CHR complex

MoMe2RCH2C

Me2RCH2C NAr

NAr

3 TfOH

- ArNH3OTf+ DME

- RCMe3

MoO

O NAr

CHCMe2R

OTf

OTf

the f irst example of a Mo=CHR complex

tBu

1987

1980

1974

Schrock catalysts

ORf

RfOMo

N

H

CMe2Ph

iPr

iPr

ORf

RfO W

N

H

t-Bu

iPriPr

SiMe3+ 2

ORf

RfO W

N

iPriPr

SiMe3

SiMe3

Schrock's catalyst for polar substrates

OF3C

F3C

Highly active tungsten catalysts

= ORf

no further reaction

Isomerism of Schrock catalysts

MoRO

RO N

C

usually favored

favored for large OR, small NR

H = 11 - 13 ppm

tBu

H

R'

R'

anti

MoRO

RO N

C

H

tBu

R'

R'

syn

favored for small OR, large NR

H = 13 - 14 ppm

Grubbs catalysts

Reference: Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18

RuCl2(PPh3)3

PhN2

Ru

PPh3

PPh3

Cl

Cl

Ph

PhPh

RuCl

ClPPh3

Ph

Ph

N N

PCy3

Cl

ClRu

Ph

Ru

PCy3

PCy3

Cl

Cl

Ph

N N

pyCl

ClRu

Ph

py

1st generation 2nd generation

PPh3

Mechanism with Grubbs catalysts

RuCl

ClPCy3

PCy3

R R'

R'

RuCl

Cy3P

PCy3

R

R'

Cl

RuCl

PCy3R

R'

Cl RuCl

PCy3

R

R'

ClR

products-

RuCl

PCy3R

R'

Cl

- PCy3

+ PCy3

- PCy3

+ PCy3Ru

ClPCy3

R

R'

ClR

products-

ROMP: Observations ROMP: strained cyclic olefins – driving force is the relief of ring strain.

It is difficult to ROMP tri- and tetrasubstituted olefins. Norbornene monomers can be synthesized from the Diels-Alder reaction of cyclopentene.

Living polymerization: block copolymers

nLnM

RLnM

RLnM

R

O

CF3

CF3 CN

COOMe

COOMe

LnM

R

O

CF3

CF3

O

F3C CF3

LnM CHR+ 100 50 100then +

50

RCM: Observations The ring to be formed cannot have appreciable strain. Reaction is intramolecular most of the times (low dilution).

Asymmetric version: Schrock-Hoveyda catalyst

N

Ph

N

Ph

+

O

O

Cy

CyMo

N

H

CMe2Ph

iPriPr

OC5H11

OC5H11

Mo

OC5H11

Comparison of catalysts

Schrock catalysts Grubbs catalysts

Less functional group tolerant

More reactive, higher rates

Asymmetric RCM works very well

Perform ene-yne metathesis

Counterparts for alkyne metathesis

More functional group tolerant, but nitriles and amines are still a problem

Less reactive, slower rates

Asymmetric RCM does not work as well

Not known

Not known

Alkyne metathesisAlthough there are two types of metal carbynes, only Mo/W compounds were found to beactive for alkyne metathesis.

Alkyne metathesis is not applied commercially because acetylenes are made by other cheapand easy methods and side reactions cannot be avoided during alkyne metathesis.

WtBuO OtBu

OtBu

R1R1 R2R2+catalyst

R2R12

LnM R

R'R'

LnMR

R'R'

MLn

R

R'R'

W tBu

tBuO

tBuOtBuO

EtEt

W

tBu

tBuO

tBuOtBuO

Et

Et

W

tBuO

tBuOtBuO

tBu Et

Et

EtEt

tBuEt Et

EtEt

Side reactions:

Reactions related to olefin metathesisPolymerization of acetylenes

Metathesis of enynes: intermolecular mechanism

MoRArN

RfORfO

R'R'

Mo

R

ArN

RfORfO

R'

R'

HMo

R

ArN

RfORfO

R'

R'

R Mo

NAr

ORfORf

R'

R'

TsNOAc

TsN

OAc

X

W

Y

+