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Kelly Wiggins21 April 2009
“Like all sciences chemistry, is marked by magic moments. For someone fortunate enough to live such a moment, it is an instant of
intense emotion: an immense field of investigation suddenly opens up before you.” –Yves Chauvin, 2005 Nobel Laureate
Metathesis Catalysis
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Outline
• History
• Mechanism
• Development of Catalysts
• Applications
• Current and Future Directions
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Carbene Crash Course
Carbene - highly active organic compound in which a carbon atom has only 6 valence electrons
R2
R1Types of Stable Carbenes
* Fischer carbenes – carbene coordinated to metal with electron withdrawing ligands
* Schrock carbenes – carbene coordinated to metal with electron donating ligands
* Persistent carbenes - N-heterocyclic carbenes (NHCs)
M
R'
R
M
R'
R
N N MesMes
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A New Reaction• 50’s and 60’s 1st observed by industrial chemists
– 1956 Eleuterio - DuPont - “looked like somebody took a pair of scissors, opened up cyclopentene and neatly sewed it up again.”
– 1960 Peters and Evering – Standard Oil Co.
– 1964 Banks and Bailey – Phillips Petroleum
• 1967 Calderon coins term “olefin metathesis”– One carbon of a double bond and all its substituents exchanges places with
a carbon of another double bond with all of its substituents
M. A. Rouhi, C&EN. 2002, 80(51), 34.R.H. Grubbs, Nobel Lecture, 2005.
*
MoCl6
Et3N
n
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• 1967–1975 What is the mechanism?
– Caulderon’s Pairwise (Conventional) Mechanism
– Chauvin’s Metallacyclobutane
N. Calderon, E. A. Olfsead, J. P. Ward, W. A. Judy, K. W. Scott, J. Am. Chem. Soc., 1968,,90, 4133
History of Olefin Metathesis
J. L. Herisson, Y. Chauvin Makromol. Chemie, 1971, 141, 162
R.H. Grubbs, Nobel Lecture, 2005. Y. Chauvin, Nobel Lecture, 2005
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• 1975 Grubbs - Deuterium Labeling
– Examined ring closing metathesis (RCM)
Mechanistic Studies
11
02
11
PairwiseChauvin
Predicted Product Ratios
R. H. Grubbs, P. L. Burk and D. D. Carr,J. Am. Chem. Soc. 1975,97,3265.T. J. Katz and R. Rothchild, J. Am. Chem. Soc. 1976,98,2519.R.H. Grubbs, Nobel Lecture, 2005
Supports Chauvin’s Mechanism!
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Chauvin’s Mechanism
Yves Chauvin
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Metallocycles
σ- bond metathesis
olefin insertion
olefin metathesis
alkyne insertion
alkyne metathesis
M CR2 M CR2M
CH2
CR2
CH2
M R
H H
M R
HH
M
H
R
H
M R M R M R M CR2M CR2 M
HC CH
CR2
M CR2M CR
CHHC
M
CH
CR
CH
Y. Chauvin, Nobel Lecture, 2005
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Span of Olefin Metathesis
Types of Metathesis
R1R 2 R1
R 2+
**
n
**
n
R 2
R1
+
R2
R1
cross metathesis (CM) ring closing metathesis (RCM)
ring opening cross metathesis (ROCM)
acyclic diene metathesis (ADMET)ring opening metathesis polymerization (ROMP)
C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.R.H. Grubbs, Nobel Lecture, 2005R.R. Schrock, Nobel Lecture, 2005Y. Chauvin, Nobel Lecture, 2005
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A Good ROMP Catalyst
• Well-defined
• Initiation faster than propagation
• Limits chain transfer and termination
• Soluble in organic media
• Show high stability to moisture, air, temperature, and a variety of organic functional groups
C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.
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ROMP Mechanism
C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.
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Chain Transfer in ROMP
C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.
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Moving toward a Catalyst
• Katz -1976 “First” well-defined catalyst
•Little MW control
•PDI > 1.85R=Ph or OMe
Katz suggested that the presence of a carbene on the catalyst
would facilitate reactivity.
Thomas J. Katz
C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.Rouhi, M. A. C&EN. 2002, 80(51), 34.
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Towards an Efficient Catalyst
Titanium– isolable metallocyclobutane
– catalyzes ROMP of norobornene with good MW control, PDI ~ 1.2
– reactive with heteroatoms
Tantalum • higher activity than Titanium
• reactive with heteroatoms
• catalyst tailoring– the bulky, electron rich aryloxides
decreased side reactions
– PDI ~ 1.1 with bulky as opposed to PDI ~ 1.6 with less bulky groups for ROMP of norbornene
Ar = 2,6-diisopropylbenzene
Ar = 2,4,6-triisopropyl benzene
C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.R.H. Grubbs, Nobel Lecture, 2005R.R. Schrock, Nobel Lecture, 2005
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Tungsten Catalysts
Basset’s Tungsten Catalyst
•wider functional group tolerance (acetates, nitriles, anhydrides)
•bulky alkoxide ligands show stereoselectivity
•high activity, increased side reactions
Schrock’s Imido-alkoxy Catalyst
•alkoxides varied to modulate activity
•limited functional group tolerance
C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.R.R. Schrock, Nobel Lecture, 2005
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Schrock’s Catalyst
•Molybdenum alkylidenes, well-defined
•highly active
•good functional group tolerance
•ester, amide, imide, ketal, ether, cyano, trifluoromethyl,
and primary halogens
•must be used in inert conditions, no water
•stereochemical control through chiral alkoxy ligands
Molybdenum Catalysts
isotactic polymer
Richard R. Schrock
C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.R.R. Schrock, Nobel Lecture, 2005
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Ruthenium Catalysts
Robert H. Grubbs
First Generation
Second Generation
Grubb’s Catalysts
•highly stable
•minimal side reactions
•e- donating lingands
•readily initiated benzylidine moiety
•increased functional group tolerance (Schrock tolerance + water, alcohols, acids)
•Selective to alkyl substituted double bonds
•ROMP highly strained rings
• σ donating NHC ligand increases electron density on the metal
•reacts with e- deficient double bonds
•more reactive, faster phosphinedissociation
•more stable, bench top ROMP
C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.R.H. Grubbs, Nobel Lecture, 2005
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Why should we care?
RCM Applications in Pharmaceuticals
R.H. Grubbs, Nobel Lecture, 2005
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But . . .we like polymers
Crosslink
R.H. Grubbs, Nobel Lecture, 2005
Dicyclopentadiene (DCPD)
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A ROMP in Water!
Water Soluble Grubb’s Catalysts
•incorporation of charged ligands allows for water solubility
•HCl promotes initiation and prevents decomposition
•PDI < 1.24 for homopolymers
C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.R.H. Grubbs, Nobel Lecture, 2005
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Summary
Mechanism of Olefin Metathesis
Grubb’s First
Generation
Grubb’s Second
Generation
Schrock’s
Catalyst
Olefin Metathesis Catalysts
most reactive
least stable
least tolerant
$ 491/ gram
least reactive
moderately stable
very tolerant
$101/gram
highly reactive
very stable
very tolerant
$316/gram
M CR2M CR2
M
CH2
CR2
CH2
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The Nobel Laureates
Yves Chauvin Institut Français du PétroleRueil-Malmaison, France
Robert H. Grubbs Richard R. Schrock Caltech
Pasadena, CAMIT
Cambridge, MA
2005 Nobel Prize in Chemistry
“for the development of the metathesis method in organic synthesis”
Y. Chauvin, Nobel Lecture, 2005 R.H. Grubbs, Nobel Lecture, 2005 R.R. Schrock, Nobel Lecture, 2005
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New and Future Directions
• Development of new catalysts– late transition metals with highly donating ligands
– ideal catalyst reacts with all cyclic olefins regardless of functionality
– “universal catalyst”
• Polymerize new monomers– tri- and tetra-substituted olefins evidence of which has been seen in RCM
• Control – structure relates to function
N NMesMes
N
O NN N PhMesMesN N MesMes
N NN N
Development of New Ligands
N
N
Fc
Fc
N
N
Fc
Fc
N
N
Ph
Ph
FcN
N
Fc
CH3
N N MesMes
OO
Fe
N
N
R
R
Development of Redox Active Ligands
E. Rosen, J. Kamplain, D. Sung, D. Varnado, C.W. Beilawski. Manuscript in preparation.C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.
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Schrock Carbene•triplet carbene•high oxidation states •early transition metals•non pi-acceptor ligands on metal •non pi-donor substituents on carbene
Fischer Carbene•singlet carbene•low oxidation state metals •middle and late transition metals •pi-electron acceptor ligands on metal•pi-donor substituents on carbene (alkoxy and alkylated amino)
M
R'
R
M
R'
R
Carbenes
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Grubb’s Idea
Ruthenium
•low oxophilicity – good functional group tolerance
•readily bonds to carbon
•RuCl3 showed increased activity in protic media
•extraordinary tolerance to polar functionality
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