Grubbs' catalyst
| 1st Generation Grubbs Catalyst | |
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| Identifiers | |
| CAS number | 172222-30-9  |
| Properties | |
| Molecular formula | C43H72Cl2P2Ru |
| Molar mass | 822.96 g mol−1 |
| Appearance | Purple solid |
| Melting point |
153 °C, 426 K, 307 °F |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
| 2nd Generation Grubbs Catalyst | |
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[1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene]dichloro(phenylmethylene)(tricyclohexylphosphine)ruthenium |
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| Identifiers | |
| CAS number | 246047-72-3 |
| Properties | |
| Molecular formula | C46H65Cl2N2PRu |
| Molar mass | 848.97 g mol−1 |
| Appearance | Pinkish brown solid |
| Melting point |
143.5-148.5 °C |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
| Infobox references | |
| 2nd Generation Hoveyda-Grubbs Catalyst | |
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| Identifiers | |
| CAS number | 301224-40-8 |
| Properties | |
| Molecular formula | C31H38Cl2N2ORu |
| Molar mass | 626.62 g mol−1 |
| Appearance | Green solid |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
| Infobox references | |
Grubbs' Catalysts are a series of transition metal carbene complexes used as catalysts for olefin metathesis. They are named after Robert H. Grubbs, the chemist who first synthesized them. There are two generations of the catalyst, as shown on the right.[1][2] In contrast to other olefin metathesis catalysts, Grubbs' catalysts tolerate other functional groups in the alkene, are air-tolerant and are compatible with a wide range of solvents.[3][4] For these reasons, Grubbs' catalysts have become popular in synthetic organic chemistry.[5]
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[edit] First generation catalyst
The First Generation Catalyst is often used in organic synthesis to achieve olefin cross-metathesis (see below), ring-opening metathesis polymerization (ROMP), acyclic diene metathesis polymerization (ADMET), and ring-closing metathesis. It is easily synthesized from RuCl2(PPh3)3,[6] phenyldiazomethane, and tricyclohexylphosphine in a one-pot synthesis.[7] Grubbs' Catalyst is a relatively stable compound in air, which makes handling very easy.
Olefin metathesis is a reaction between two molecules containing double bonds. The groups bonded to the carbon atoms of the double bond are exchanged between molecules, to produce two new molecules containing double bonds with swapped groups. Whether a cis isomer or trans isomer is formed in this type of reaction is determined by the orientation the molecules assume when they coordinate to the catalyst, as well as the sterics of the substituents on the double bond of the newly forming molecule. Other catalysts are effective for this reaction, notably those developed by Richard R. Schrock (Schrock carbene).
[edit] Second generation catalyst
The Second Generation Catalyst has the same uses in organic synthesis as the First Generation Catalyst, but generally with higher activity. This catalyst is stable toward moisture and air, thus is easier to handle in the lab. A catalyst based on an unsaturated N-heterocyclic carbene (1,3-bis(2,4,6-trimethylphenyl)dihydroimidazole) was reported in March 1999 by Nolan's group.[8] Grubbs' group reported a catalyst based on a saturated N-heterocyclic carbene (1,3-bis(2,4,6-trimethylphenyl)imidazolidine) later the same year[6] (August 1999). One phosphine ligand is replaced with an N-heterocyclic carbene (NHC) and in this case ruthenium is coordinated to two carbene groups. Both generations of the catalyst are commercially available, along with many derivatives of the second generation catalyst.
[edit] Hoveyda-Grubbs Catalyst
In the first generation Hoveyda-Grubbs Catalyst, one of the phosphine ligands is replaced by an isopropyloxy group attached to the benzene ring. Its second generation has the other phosphine ligand replaced by NHC.
In one study a water soluble Grubbs catalyst is prepared by attaching a polyethylene glycol chain to the imidazoline group. The imidazolinium salt is deprotonated by potassium hexamethyldisilazide (KHMDS) in situ to give the N-heterocyclic carbene, which displaces one phosphine ligand to give the modified ruthenium complex:[9]
This catalyst is used in the ring-closing metathesis reaction in water of a diene carrying an ammonium salt group making it water-soluble as well.
[edit] Fast-Initiating Catalysts
The initiation rate of the Grubbs' catalyst can be altered by replacing the phosphine ligand with more labile pyridine ligands. By using 3-bromopyridine the initiation rate is increased more than a million fold:[10]
The principle application of the fast-initiating catalysts is as initiators for ring opening metathesis polymerisation (ROMP). Because of their usefulness in ROMP these catalysts are sometimes referred to as the 3rd generation Grubbs' catalysts.[11] The high ratio of the rate of initiation to the rate of propagation makes these catalysts useful in living polymerization. Living polymerization can be used in the synthesis of block copolymers with interesting side chain functionality, taking full advantage of the high functional group tolerance of the Grubbs' catalyst.
[edit] Applications
An interesting application of Grubbs' Catalyst is in the aerospace industry. A spaceship's hull is a necessarily very strong material, but over time microcracks in the structure can form. A new material, with potential application in the construction of spaceship hulls, contains Grubbs' Catalyst, as well as capsules of dicyclopentadiene, which can undergo ROMP. When a crack in the hull forms, the capsules are ruptured and come into contact with Grubbs' Catalyst, which polymerizes dicyclopentadiene and seals the crack.[12]
On October 5, 2005, Grubbs, Richard R. Schrock and Yves Chauvin won the Nobel Prize in Chemistry in recognition of their contributions to the development of this widely used process.
[edit] References
- ^ Grubbs, Robert H. (2003). Handbook of Metathesis (1st ed.). German: Wiley-VCH. ISBN 3527306161.
- ^ Grubbs, R.H.; Trnka, T.M.: Ruthenium-Catalyzed Olefin Metathesis in "Ruthenium in Organic Synthesis" (S.-I. Murahashi, Ed.), Wiley-VCH, Germany, 2004.
- ^ Vougioukalakis, G. C.; Grubbs, R. H. (2010). "Ruthenium-Based Heterocyclic Carbene-Coordinated Olefin Metathesis Catalysts". Chem. Rev. 110 (3): 1746–1787. doi:10.1021/cr9002424. PMID 20000700.
- ^ Trnka, T. M.; Grubbs, R. H. (2001). "The Development of L2X2Ru=CHR Olefin Metathesis Catalysts: An Organometallic Success Story". Accounts of Chemical Research 34 (1): 18–29. doi:10.1021/ar000114f. PMID 11170353.
- ^ Cossy, Janine; Arseniyadis, Stellios; Meyer, Christophe (2010). Metathesis in Natural Product Synthesis: Strategies, Substrates and Catalysts (1st ed.). Germany: Wiley-VCH. ISBN 3527324402.
- ^ a b Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. (1999). "Synthesis and Activity of a New Generation of Ruthenium-Based Olefin Metathesis Catalysts Coordinated with 1,3-Dimesityl-4,5-dihydroimidazol-2-ylidene Ligands". Organic Letters 1 (6): 953–956. doi:10.1021/ol990909q.
- ^ Schwab, P.; Grubbs, R. H.; Ziller, J. W. (1996). "Synthesis and Applications of RuCl2(=CHR')(PR3)2: The Influence of the Alkylidene Moiety on Metathesis Activity". Journal of the American Chemical Society 118 (1): 100–110. doi:10.1021/ja952676d.
- ^ Jinkun Huang,, Edwin D. Stevens,, Steven P. Nolan,, and, Jeffrey L. Petersen (1999). "Olefin Metathesis-Active Ruthenium Complexes Bearing a Nucleophilic Carbene Ligand". Journal of the American Chemical Society 121 (12): 2674–2678. doi:10.1021/ja9831352.
- ^ Soon Hyeok Hong and Robert H. Grubbs (2006). "Highly Active Water-Soluble Olefin Metathesis Catalyst". Journal of the American Chemical Society 128 (11): 3508–3509. doi:10.1021/ja058451c. PMID 16536510.
- ^ Love, Jennifer A.; Morgan, John P.; Trnka, Tina M.; Grubbs, Robert H. (2002). "A Practical and Highly Active Ruthenium-Based Catalyst that Effects the Cross Metathesis of Acrylonitrile". Angew. Chem. Int. Edit. 41 (21): 4035-4037. doi:10.1002/1521-3773(20021104)41:21<4035::AID-ANIE4035>3.0.CO;2-I.
- ^ Leitgeb, Anita; Wappel, Julia; Slugovc, Christian (2010). "The ROMP toolbox upgraded". Polymer 51 (14): 2927-2946. doi:10.1016/j.polymer.2010.05.002.
- ^ S.R. White, N.R. Sottos, P.H. Geubelle, J.S. Moore, M.R. Kessler, S.R. Sriram, E.N. Brown, S. Viswanathan (2001). "Autonomic healing of polymer composites". Nature 409 (6822): 794–797. doi:10.1038/35057232. PMID 11236987.
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