Karstedt's catalyst, CAS 11057-89-9 (PubChem CID 10959889, formula C8H18OPtSi2, MW 381.48 g/mol), is a platinum(0) divinyltetramethyldisiloxane complex and the dominant industrial catalyst for silicone hydrosilylation, run at roughly 0.5 to 10 ppm platinum by mass. Its structure, platinum content, properties, preparation, catalytic cycle, commercial form and hazard classification follow below.
What Is Karstedt Catalyst?#
Karstedt's catalyst is a platinum(0) complex of divinyltetramethyldisiloxane (DVTMS), registered under CAS 11057-89-9 and cataloged by PubChem as CID 10959889 with the formula C8H18OPtSi2 (MW 381.48 g/mol), per Wikipedia's Karstedt's catalyst entry. It belongs to the platinum group metal compounds and catalysts cataloged on this site; its full structure, a two-platinum complex rather than the single-platinum unit the registered formula implies, follows next.
| Property | Value |
|---|---|
| Preferred name | Karstedt's catalyst |
| Alternate names | platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex; Karstedt catalyst |
| CAS number | 11057-89-9 |
| PubChem CID | 10959889 |
| PubChem IUPAC name | ethenyl-[ethenyl(dimethyl)silyl]oxy-dimethylsilane;platinum |
| InChIKey | RCNRJBWHLARWRP-UHFFFAOYSA-N |
| Registered formula | C8H18OPtSi2 |
| Molecular weight (registered) | 381.48 g/mol |
| Platinum group metal | platinum (Pt), element 78 |
Karstedt Catalyst Structure and Bonding#
Karstedt's catalyst forms a binuclear platinum(0) complex, Pt2[(Me2SiCH=CH2)2O]3 (C24H54O3Pt2Si6, MW 949.4 g/mol, PubChem CID 178184125), in which two platinum centers are each surrounded by three alkene donor groups from three bridging DVTMS ligands, per Wikipedia's citation of Lewis and Colborn's 1995 crystallographic study in Organometallics. Each platinum atom sits approximately coplanar with its six coordinated alkene carbons, confirmed by X-ray crystallography. The registered formula C8H18OPtSi2 (CAS 11057-89-9, CID 10959889) is a single-platinum repeat unit rather than the full dimer; both describe the same catalyst, and this page uses the registered formula for its identity fields and the dimeric formula for the structure above.
The platinum(0) oxidation state, rather than the platinum(II) or platinum(IV) states of older hydrosilylation catalysts, lets the complex enter the catalytic cycle described under Uses without a separate reduction step.
Platinum Content of Karstedt Catalyst#
Platinum makes up 51.1% of Karstedt's catalyst by mass on the registered single-platinum formula (C8H18OPtSi2, MW 381.48 g/mol), or 41.1% on the basis of the actual binuclear complex (C24H54O3Pt2Si6, MW 949.4 g/mol), and neither figure describes the diluted commercial solution sold at scale. Platinum's atomic weight, 195.084 g/mol, divided by 381.48 g/mol gives 51.1 wt%, tied to the registered formula; the same atomic weight for two platinum centers, 390.168 g/mol, divided by the dimer's 949.4 g/mol gives 41.1 wt%, tied to the crystallographically confirmed structure. Sigma-Aldrich's named grade, product 479519, lists a far lower content, approximately 2 wt% platinum in xylene. Current pricing for the metal is on DailyPlatinum's platinum price today page.
Physical and Chemical Properties#
Karstedt's catalyst is a colorless solid in its pure discrete-complex form, soluble in silicones, xylene and toluene, according to Wikipedia's Karstedt's catalyst entry; the pale-yellow-to-amber color associated with the catalyst commercially belongs to the diluted commercial solutions, not the pure complex. A melting or decomposition point for the pure complex is not established: Wikipedia's own infobox lists a 12 to 13°C melting point, a 139°C boiling point and a 1.74 g/cm3 density, but those figures conflict with the same article's description of the complex as a room-temperature solid and closely resemble the free DVTMS ligand's constants rather than the platinum complex's, so this page does not publish them as verified.
| Property | Value | Basis |
|---|---|---|
| Appearance (discrete complex) | Colorless solid | Wikipedia; chemistry registry |
| Appearance (commercial solution) | Amber to pale-yellow liquid | Chemistry registry (CAS 68478-92-2) |
| Solubility | Soluble in silicones, xylene, toluene | Chemistry registry |
| Melting/decomposition point | Not established from a reliable source | Wikipedia infobox flagged as internally inconsistent |
| Molecular weight | 381.48 g/mol (registered formula); 949.4 g/mol (binuclear complex) | PubChem CID 10959889; CID 178184125 |
| Coordination | Two Pt(0) centers, three bridging DVTMS ligands, Pt approximately coplanar with six alkene carbons | Wikipedia, citing Lewis and Colborn (1995) |
How Is Karstedt Catalyst Made?#
Karstedt's catalyst is made from anhydrous platinum(II) chloride (PtCl2) reacted with divinyltetramethyldisiloxane (DVTMS) in a polar solvent such as methyl ethyl ketone (MEK), according to a 2023 ACS Catalysis study on the synthesis mechanism. The traditional route runs 8 to 10 hours and converts only 80 to 85% of the platinum(II) chloride, with the catalyst thermally decomposing over the extended run. Presoaking or milling the platinum(II) chloride in MEK at room temperature first forms a crystalline intermediate, Pt6Cl12·(MEK)1.5, and starting from that intermediate instead raises conversion to 99% in just 4 hours, per the same study. Speier's catalyst, made from chloroplatinic acid rather than platinum(II) chloride, uses a different precursor route, covered on this site's Speier catalyst page.
What Is Karstedt Catalyst Used For?#
Karstedt's catalyst is used for silicone hydrosilylation, the addition of silicon-hydrogen bonds across carbon-carbon double bonds, per Wikipedia's hydrosilylation entry. Industrial formulations run it at roughly 0.5 to 10 ppm platinum by mass for ambient-temperature cure, per patent literature on silicone formulations, with some formulations reaching a floor of 0.001 parts by weight platinum per million parts of the composition, below 1 part per billion. As a homogeneous catalyst, it belongs to the same broad family of PGM catalysts in chemistry covered elsewhere on this site.
The complex cures four related classes of product:
- Addition-cure silicone elastomers: forms Si-CH2-CH2-Si crosslinks with no by-product, unlike condensation-cure silicones that release acetic acid or alcohol.
- Release liners: cured silicone coatings on paper and film backings.
- Medical-grade tubing: platinum-cured silicone tubing for medical and laboratory use.
- LED optical encapsulants and silane coupling agents: further hydrosilylation applications beyond bulk elastomer curing.
Karstedt's catalyst largely displaced Speier's catalyst because it dissolves directly into the silicone substrate rather than needing a polar carrier solvent, per Wikipedia.
Catalytic Cycle#
The Karstedt's catalyst hydrosilylation cycle runs through the Chalk-Harrod mechanism: oxidative addition of a silicon-hydrogen bond to platinum, migratory insertion of the coordinated alkene into the platinum-hydride bond, and reductive elimination forming the new silicon-carbon bond, per MDPI Polymers (2020) and a 1999 Inorganica Chimica Acta theoretical study.
- Add the substrate's Si-H bond oxidatively across the platinum(0) center, forming a hydride-silyl intermediate.
- Coordinate the alkene at platinum, then migrate the platinum-bound hydride onto it, forming a platinum-alkyl bond in the rate-determining step.
- Eliminate reductively: the alkyl group combines with the silyl ligand to form the new Si-C bond, regenerating the platinum(0) catalyst.
A modified Chalk-Harrod route, inserting the alkene into the platinum-silicon bond instead, accounts for the vinylsilane byproducts seen in real production, per the same sources.
Rhodium-based Wilkinson catalyst also catalyzes hydrosilylation, chosen instead of platinum where platinum's selectivity is inadequate for the substrate.
Commercial Forms, Purity and Price#
Karstedt's catalyst is sold commercially as a dilute platinum(0) solution registered under the separate CAS 68478-92-2, typically carried in xylene or in vinyl-terminated polydimethylsiloxane (PDMS) fluid, according to Sigma-Aldrich's product listing; the discrete complex (CAS 11057-89-9) is not the form sold at industrial scale. Sigma-Aldrich's product 479519, "platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex, xylene," names a specific commercial grade at approximately 2 wt% platinum.
| Grade | CAS | Form | Platinum content |
|---|---|---|---|
| Discrete complex (reference/research use) | 11057-89-9 | Colorless solid | 51.1 wt% (registered formula) or 41.1 wt% (binuclear complex) |
| Commercial dilute solution | 68478-92-2 | Amber liquid, xylene or PDMS carrier | Low single-digit wt%; Sigma-Aldrich product 479519 lists approximately 2 wt% |
Safety and Hazard Classification#
PubChem's own record for CID 10959889 lists no GHS signal word and no hazard codes on file, but the commercial dilute solution sold under CAS 68478-92-2 carries the signal word Danger, with hazard statements H226 (flammable liquid and vapor), H304 (may be fatal if swallowed and enters airways), H312 (harmful in contact with skin), H315 (skin irritation), H319 (serious eye irritation), H332 (harmful if inhaled), H335 (respiratory irritation) and H373 (organ damage risk on prolonged exposure), per Wikipedia, corroborated by supplier safety data sheets. GHS classification reported to PubChem for CID 10959889: no signal word, no hazard codes, zero notifications on file; the classification above belongs to the commercial solution, not the bare PubChem record.
No EPA CompTox identifier or PubChem Safety and Hazards record exists for either CID, so handlers rely on the supplier SDS for the grade purchased.
Where Karstedt Catalyst Chemistry Stops: Medical and Pharmaceutical Platinum#
This page covers Karstedt's catalyst as an industrial hydrosilylation reagent only, not as a platinum-based drug or a jewelry-plating agent. Platinum-based pharmaceuticals such as cisplatin are a separate pharmacological subject, covered on this site's platinum compounds page, without dosing or clinical detail. It is also unrelated to the fixed-bed three-way catalyst and diesel oxidation catalyst used in vehicle exhaust systems, which run heterogeneous, not homogeneous, chemistry.
Related PGM Compounds#
Karstedt's catalyst shares its platinum(0) hydrosilylation chemistry with Speier's catalyst, its chloroplatinic acid-based predecessor, and with the site's other named homogeneous PGM catalysts.
| Compound | Formula / composition | Relationship to Karstedt's catalyst |
|---|---|---|
| Speier catalyst | H2PtCl6 (chloroplatinic acid), CAS 16941-12-1 | The platinum(IV) predecessor Karstedt's catalyst displaced for most addition-cure silicone manufacturing |
| Pearlman catalyst | Pd(OH)2 on carbon, CAS 12135-22-7 | A palladium hydrogenation catalyst; different metal and reaction, same era of PGM catalyst development |
| Lindlar catalyst | Pd on CaCO3, lead-poisoned, CAS 53092-86-7 | A heterogeneous palladium alkyne-to-alkene catalyst, contrasting with Karstedt's homogeneous platinum chemistry |
| Wilkinson catalyst | RhCl(PPh3)3, CAS 14694-95-2 | A rhodium(I) homogeneous catalyst also used for hydrosilylation where platinum selectivity is inadequate |
| Crabtree catalyst | Iridium(I) cationic complex, CAS 64536-78-3 | An iridium homogeneous hydrogenation catalyst from the same era of PGM complex chemistry |
| Grubbs catalyst | RuCl2(PCy3)2(=CHPh), CAS 172222-30-9 (1st generation) | A ruthenium homogeneous catalyst for olefin metathesis rather than hydrosilylation |
| Hoveyda Grubbs catalyst | C31H38Cl2N2ORu, CAS 301224-40-8 (2nd generation) | A phosphine-free ruthenium metathesis catalyst descended from the Grubbs family |
| Noyori catalyst | Ruthenium-BINAP asymmetric hydrogenation complex | A ruthenium asymmetric-hydrogenation catalyst from the same homogeneous PGM catalyst tradition |
History#
Karstedt's catalyst was developed by Bruce D. Karstedt at General Electric in the early 1970s, patented as US Patent 3,775,452, "Platinum complexes of unsaturated siloxanes and platinum containing organopolysiloxanes," filed 28 April 1971 and granted 27 November 1973, per the patent record and Wikipedia. Its advantage over Speier's earlier chloroplatinic acid catalyst is that it dissolves directly into silicone substrates instead of needing a polar carrier solvent, which is why it became the most commonly used catalyst in the silicone industry, per the Johnson Matthey Platinum Metals Review lineage on platinum catalysts in silicones.