Olefin Metathesis Catalysis

Fan Qi A0048267XGS5002 Journal Club

Outline History Mechanism Catalysts Applications

Yves Chauvin Robert H. Grubbs Richard R. Schrock

Overview on Olefin Metathesis This reaction can be thought of as a reaction

where all the C=C bonds are cleaved and then rearranged in a statistical fashion.

History 1956 H.S. Eleuterio – DuPont: Ring Opening Reaction

observed

1964 Banks and Bailey – Phillips Petroleum

1967 Chalderon coined the 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

R.H. Grubbs, Nobel Lecture, 2005. M. A. Rouhi, C&EN. 2002, 80(51), 34.

Mechanism – Initial Work Calderon’s Pairwise (conventional) Mechanism

Chauvin’s Metallacyclobutane• Suggested the metal-carbene intermediate exists

J. Am. Chem. Soc., 90, 4133 (1968)

Y. Chauvin, Nobel Lecture, 2005

Mechanism – Initial Work Grubbs – Deuterium Labeling

• Examined ring closing metathesis (RCM)

Pair-wise Chauvin1 10 21 1

Predicted Ratio

ObservedThe experiment supports Chauvin’s Mechanism

Mechanism – Chauvin’s Direct [2+2] cycloaddition of two alkenes is symmetric

forbidden. 1970’s Chauvin proposed the widely accepted Mechanism

reactant  1

reactant  2

Intermediate

Metallocycle

Y. Chauvin, Nobel Lecture, 2005

product  1

product  2

Mechanism – Chauvin’s

Makromol. Chem., 141, 161 (1971)

Ideal Catalyst Produces an infinite amount of product from a

single catalyst molecule 100% conversion rate Show high stability to moisture, air, temperature

etc. 0 by-products Soluble in organic media Cheap for industrial use

C.W. Bielawski, R.H. Grubbs Prog. Polym. Sci. 32 (2007) 1.

Catalyst 1976 – Katz “First” well-defined catalyst

Katz suggested that the presence of a carbene on the catalyst would facilitate reactivity

J. Am. Chem. Soc., 97, 1592 (1975)

Catalyst 1986 – Grubbs group using Tebbe Reagent

• The core metal is Titanium• Isolable metallocyclobutane• catalyzes ROMP of norbornene with good MW control, PDI ~ 1.2• reactive with heteroatoms

L. R. Gilliom and R. H. Grubbs, J. Am. Chem. Soc. 1986, 108, 733.

Catalyst Tungsten Based Catalyst

• 1988, Schrock’s Imido-alkoxy Alkoxides varied to modulate activity Limited functional group tolerance

• 1995, Basset’s Catalyst Bulky alkoxide ligands show stereoselectivity Better function group tolerance (acetates, nitriles, anhydrides) High activity

R. R. Shrock and Amir H. Hoveyda, ACIE, 2003, 42-38, 4592

Commercialized Catalysts 1990 - Schrock’s Catalyst

• Molybdenum alkylidenes• Highly active• Good functional group tolerance• Strict inert conditions, no water• Sterochemical control through chiral alkoxy ligands

R.R. Schrock, Nobel Lecture, 2005

Commercialized Catalysts 1992 – 2002 Grubb’s Catalysts

• Highly stable• Minimal side reactions• Electron donating lingands• Readily initiated benzylidyne moiety• Increased functional group tolerance (Schrock tolerance

+ water alcohols, acids)

R.R. Schrock, Nobel Lecture, 2005

Catalyst SummarySCHROCK’S CATALYST

Most reactive Least stable Least tolerant Most expensive

Lest reactive Moderately

stable Very tolerant Least expensive

Grubb’s 1st Generation

Highly reactive Very stable Very tolerant Less expensive

Grubb’s 2nd Generation

Olefin Metathesis Applications Wide range of applications

• From baseball bat to pharmaceutical agents Example 1:

• Drugs of treating hepatitis C

Example 2:• Polymerization of DCPD

R.R. Schrock, Nobel Lecture, 2005

Thank youQ & A