Grubbs catalyst is the name for two ruthenium carbene complexes, first and second generation, that initiate olefin metathesis by exchanging carbon-carbon double bonds between alkene molecules. Robert H. Grubbs, Richard R. Schrock and Yves Chauvin shared the 2005 Nobel Prize in Chemistry for developing the metathesis method these catalysts run, and ruthenium accounts for roughly 12% of either complex by mass. The first generation carries CAS number 172222-30-9 and the second carries CAS number 246047-72-3, two distinct compounds rather than two names for one substance. Their structures, ruthenium content, physical properties, preparation, industrial uses and commercial forms follow below, generation by generation.
What Is Grubbs Catalyst?#
Grubbs catalyst is a common name covering two distinct ruthenium(II) carbene complexes, each with its own CAS registry number, that chemists use to initiate olefin metathesis in solution. The first-generation complex, RuCl2(PCy3)2(=CHPh), is CAS number 172222-30-9 and PubChem CID 6392641; the second-generation complex, RuCl2(H2IMes)(PCy3)(=CHPh), is CAS number 246047-72-3 and PubChem CID 11147261. Both compounds sit among the platinum group metal compounds and catalysts cataloged on this site, and both identify ruthenium, platinum group metal element 44, as their catalytic center.
PubChem depicts the first-generation complex, CID 6392641, as the doubly charged ionic fragment C43H74Cl2P2Ru+2 (825 g/mol), splitting each tricyclohexylphosphine ligand into its protonated phosphonium form rather than drawing the neutral molecule; chemists write the neutral complex as RuCl2(PCy3)2(=CHPh), the conventional formula used throughout this page, with a molecular weight of 822.96 g/mol. The second-generation complex resolves on PubChem to its neutral formula directly, C46H65Cl2N2PRu, at 848.98 g/mol.
| Property | 1st generation | 2nd generation |
|---|---|---|
| Conventional formula | RuCl2(PCy3)2(=CHPh) | RuCl2(H2IMes)(PCy3)(=CHPh) |
| CAS number | 172222-30-9 | 246047-72-3 |
| PubChem CID | 6392641 | 11147261 |
| PubChem depiction | Ionic fragment C43H74Cl2P2Ru+2 | Resolves to neutral formula |
| Molecular weight | 822.96 g/mol | 848.98 g/mol |
| Ligand set | 2x tricyclohexylphosphine (PCy3), 1x benzylidene, 2x chloride | 1x PCy3, 1x N-heterocyclic carbene (H2IMes), 1x benzylidene, 2x chloride |
| First reported | 1995 | 1999 |
| Platinum group metal | ruthenium (Ru), element 44 | ruthenium (Ru), element 44 |
Grubbs Catalyst Structure and Bonding#
Grubbs catalysts adopt a five-coordinate, distorted square-pyramidal geometry around a ruthenium(II) center, a d6, 16-electron configuration, per Wikipedia's Grubbs catalyst entry. A benzylidene group (=CHPh) occupies the apical position, two chloride ions and two phosphorus- or nitrogen-donor ligands fill the basal sites, and the complex stays coordinatively unsaturated, with one site free to bind an incoming alkene.
The two generations differ in only one basal ligand: the first generation carries two tricyclohexylphosphine (PCy3) ligands, while the second replaces one of them with a saturated N-heterocyclic carbene, H2IMes, a substitution that raises thermal stability and functional-group tolerance without changing ruthenium's oxidation state or coordination number. One phosphine ligand dissociates reversibly in solution ahead of catalysis, opening the site that starts the metathesis cycle described below.
Ruthenium Content of Grubbs Catalyst#
Ruthenium makes up 12.3% of the first-generation Grubbs catalyst and 11.9% of the second generation by mass. Ruthenium's standard atomic weight, 101.07 g/mol, divided by each complex's molecular weight gives the fraction: 101.07 / 822.96 = 0.123 (12.3%) for the first generation, and 101.07 / 848.98 = 0.119 (11.9%) for the second, using the conventional formula and molecular weight for each compound rather than PubChem's ionic-fragment depiction. That fraction matters commercially because both catalysts are evaluated against their contained-ruthenium value, tracking the metal whose ruthenium price today sets the underlying cost base.
Physical and Chemical Properties#
Grubbs catalyst appears as a bright purple powder in its first generation and a brown to very dark brown or red solid in its second, according to ChemicalBook's aggregated technical data for each generation. Both generations dissolve only slightly in common organic solvents and both carry a recommended storage temperature of 2 to 8 degrees Celsius to limit decomposition.
| Property | 1st generation (CAS 172222-30-9) | 2nd generation (CAS 246047-72-3) |
|---|---|---|
| Appearance | Bright purple powder | Brown to very dark brown/red solid |
| Melting point | 153 C (decomposition) | 143.5-148.5 C |
| Solubility | Slightly soluble in chloroform; sparingly soluble in dichloromethane | Slightly soluble in chloroform and ethyl acetate; very slightly soluble in hot methanol |
| Recommended storage | 2-8 C | 2-8 C |
| Molecular weight | 822.96 g/mol | 848.98 g/mol |
ChemicalBook's technical data pages for each generation are the source for these appearance, melting point and solubility figures; PubChem does not list a melting point for either compound.
How Is Grubbs Catalyst Made?#
Grubbs catalyst is made starting from ruthenium(III) chloride hydrate, RuCl3.xH2O, the universal ruthenium precursor for the whole Grubbs family. That hydrate is first converted into dichlorotris(triphenylphosphine)ruthenium(II), RuCl2(PPh3)3, an intermediate this site's chemistry registry names specifically for its role in Grubbs precursor chemistry.
The preparation runs in three linked steps:
- Convert ruthenium(III) chloride hydrate into the triphenylphosphine intermediate RuCl2(PPh3)3.
- Exchange the triphenylphosphine ligands for tricyclohexylphosphine (PCy3) and install a benzylidene (=CHPh) group at ruthenium, giving the first-generation catalyst, RuCl2(PCy3)2(=CHPh).
- React the first-generation catalyst with a free N-heterocyclic carbene ligand, H2IMes, which displaces one PCy3 to give the second-generation catalyst, RuCl2(H2IMes)(PCy3)(=CHPh).
The second generation is therefore made from the first, not independently from the ruthenium precursor.
What Is Grubbs Catalyst Used For?#
Grubbs catalyst is used for olefin metathesis, the catalytic exchange of carbon-carbon double bonds between alkenes, covering three named reaction types: ring-closing metathesis (RCM), ring-opening metathesis polymerization (ROMP) and cross metathesis (CM). The earliest commercial application was ROMP of strained cycloolefins, notably dicyclopentadiene, per Sigma-Aldrich's Aldrichimica Acta technical literature on ruthenium metathesis catalysts, before the reaction family broadened into fine-chemical and specialty-polymer manufacturing.
At industrial scale, Materia, the company Grubbs co-founded to commercialize the catalysts, formed Elevance Renewable Sciences with Cargill in 2008 to run plant-oil-to-specialty-chemical olefin metathesis with Grubbs-type catalysts, building on a 2003 Materia-Cargill collaboration, according to Chemical & Engineering News. Elevance opened a metathesis-based chemical plant in Gresik, Indonesia, in 2013, converting palm and vegetable oils into specialty chemicals at production volume. Fragrance manufacturers also use ring-closing and cross metathesis with Grubbs-type catalysts to build macrocyclic musk compounds, including routes to Exaltolide-type sixteen-membered macrolactone musks, replacing classical syntheses that are often lower-yielding or more toxic, according to a review in Russian Chemical Reviews.
As a homogeneous catalyst dissolved fully in the reaction solvent, Grubbs catalyst belongs to a different family from the fixed-bed PGM catalysts in chemistry used in industrial reactors and vehicle exhaust systems, which run heterogeneous, surface-bound chemistry instead.
Catalytic Cycle#
The Grubbs catalytic cycle runs on the Chauvin mechanism, named for Yves Chauvin's Nobel-cited proposal: ligand dissociation, [2+2] cycloaddition and retro-[2+2] cycloreversion, repeated for every double bond exchanged.
- Dissociate one phosphine ligand from the resting 16-electron ruthenium benzylidene complex, opening a coordination site.
- Coordinate an alkene substrate at that open site, next to the ruthenium-carbene (Ru=CHPh) bond.
- Form a four-membered metallacyclobutane ring through a [2+2] cycloaddition between the ruthenium carbene and the coordinated alkene.
- Open the metallacyclobutane the other way, a retro-[2+2] cycloreversion that releases a new alkene carrying the exchanged carbon fragment and regenerates a ruthenium carbene ready to re-enter the cycle.
Ring-closing metathesis repeats this cycle intramolecularly and releases ethylene to close a ring; ring-opening metathesis polymerization repeats it on a strained cyclic alkene, where relief of ring strain drives chain growth; cross metathesis repeats it between two separate acyclic alkenes to swap their substituents.
Turnover number sets the economics of scaled-up metathesis more than catalyst loading does. In a solvent-free comparison of 1-octene self-metathesis, Dinger and Mol, writing in Advanced Synthesis & Catalysis in 2002, measured turnover numbers for the second-generation catalyst about five times higher than for the first generation, with both retaining high selectivity for the dimer product 7-tetradecene; a bulkier NHC-ligated variant in the same study exceeded a turnover number of 640,000, a figure specific to that modified variant rather than the parent second-generation complex.
Commercial Forms, Purity and Price#
Grubbs catalyst ships as a solid research and fine-chemical reagent, sold by name-brand suppliers rather than as a generic commodity powder. Both generations are established commercial catalysts, not research curiosities: Sigma-Aldrich, Materia, American Elements, Strem and Umicore all sell one or both generations, and production runs from milligram laboratory packs to multi-kilogram and larger industrial batches for olefin metathesis manufacturing, according to Chemical & Engineering News. Umicore, one of those producers, markets the two generations under the trade names Grubbs Catalyst M102 and Grubbs Catalyst M204, matching Sigma-Aldrich products 579726 (CAS 172222-30-9) and 569747 (CAS 246047-72-3) respectively, according to Sigma-Aldrich and Umicore catalog listings.
| Generation | Form | Typical grade | Umicore trade name | Pack size class |
|---|---|---|---|---|
| 1st generation | Purple solid powder | Catalysis / research grade | Grubbs Catalyst M102 | Milligram to multi-gram lab packs; multi-kilogram for contract manufacture |
| 2nd generation | Brown to dark red/brown solid | Catalysis / research grade, higher air stability | Grubbs Catalyst M204 | Milligram to multi-gram lab packs; multi-kilogram for contract manufacture |
Safety and Hazard Classification#
GHS classification reported to PubChem: no signal word, no hazard statement codes, zero notifications on file for CID 6392641, the first-generation complex. That absence is not a certification of safety; it means no classification has been registered for this specific PubChem entry.
ChemicalBook's aggregated technical data lists both generations under transport hazard class 4.1 (flammable solid), packing group II, with GHS hazard statement H228, and both are listed under the US Toxic Substances Control Act (TSCA). The second-generation complex also carries a Carc. 1B (inhalation route) carcinogenicity classification from ChemicalBook that the first generation does not. A REACH or CLP classification specific to either generation is not established in the sources reviewed for this page; laboratories still handle both solids under standard precautions, gloves and fume-hood practice, with dust not inhaled.
Where Grubbs Catalyst Chemistry Stops: Medical and Pharmaceutical Platinum#
This page covers Grubbs catalyst as a laboratory and industrial reagent only, not as a component of any platinum-based pharmaceutical or a catalytic converter. Platinum-based drugs such as cisplatin are a distinct pharmacological subject, covered elsewhere on this site without dosing or clinical detail. Grubbs catalyst is also unrelated to the fixed-bed three-way catalyst or diesel oxidation catalyst used in vehicle exhaust systems, both solid-supported, heterogeneous PGM catalysts rather than the dissolved molecular complex described here.
Related PGM Compounds#
Grubbs catalyst shares ruthenium-carbene chemistry with one phosphine-free sibling catalyst on this site, and its era of homogeneous PGM catalyst development with several other named catalysts here.
| Compound | Formula / composition | Relationship to Grubbs catalyst |
|---|---|---|
| Hoveyda-Grubbs catalyst | C31H38Cl2N2ORu, CAS 301224-40-8 (2nd generation) | A phosphine-free variant replacing PCy3 with a chelating isopropoxy-benzylidene ligand, improving bench stability at the cost of slower initiation |
| Wilkinson catalyst | RhCl(PPh3)3, CAS 14694-95-2 | Same era of homogeneous PGM catalyst chemistry, hydrogenation instead of metathesis, rhodium instead of ruthenium |
| Lindlar catalyst | Pd on CaCO3, lead-poisoned | A heterogeneous alkyne-to-alkene hydrogenation catalyst, contrasting with Grubbs catalyst's homogeneous, dissolved chemistry |
| Crabtree catalyst | C31H50F6IrNP2-, CAS 64536-78-3 | An iridium(I) hydrogenation catalyst from the same homogeneous-catalyst family, active on hindered alkenes rather than in metathesis |
Grubbs catalyst is one entry in a wider catalog of ruthenium compounds on this site, alongside other named PGM catalysts such as the Karstedt catalyst, Speier catalyst, Pearlman catalyst and Noyori catalyst, each built around a different platinum group metal and reaction class.
History#
Robert H. Grubbs built on his own group's earlier work: in 1992, Nguyen, Johnson, Grubbs and Ziller reported in the Journal of the American Chemical Society a bis(triphenylphosphine) ruthenium carbene complex, the first well-defined, single-component ruthenium metathesis catalyst, running ROMP of norbornene in protic media, including water. Grubbs reported the practical, air-tolerant first-generation catalyst, RuCl2(PCy3)2(=CHPh), in 1995, and the second generation followed in 1999, replacing one phosphine with the N-heterocyclic carbene ligand H2IMes. He shared the 2005 Nobel Prize in Chemistry with Yves Chauvin and Richard R. Schrock for developing the metathesis method these catalysts made practical. Materia, Inc., the company Grubbs co-founded in 1999 to commercialize the Caltech technology, later built the Proxima line of polydicyclopentadiene ROMP thermoset resins for composites and pipeline insulation, before ExxonMobil Chemical Company acquired Materia in December 2021, per ExxonMobil's own press release.
Frequently Asked Questions#
Did Robert H. Grubbs win a Nobel Prize? Yes. Grubbs shared the 2005 Nobel Prize in Chemistry with Yves Chauvin and Richard R. Schrock for developing the olefin metathesis method that his catalysts run.
What is the second-generation Grubbs catalyst used for? The second-generation catalyst, RuCl2(H2IMes)(PCy3)(=CHPh), is used for the same three metathesis reaction types as the first generation, ring-closing metathesis, ring-opening metathesis polymerization and cross metathesis, but with higher thermal stability and broader functional-group tolerance because its N-heterocyclic carbene ligand survives harsher conditions than the first generation's second phosphine.
What does Grubbs catalyst do? Grubbs catalyst catalyzes olefin metathesis, breaking and reforming carbon-carbon double bonds so that two alkene molecules exchange substituents through a metallacyclobutane intermediate, the Chauvin mechanism described above.