Heraeus` Metal Compounds for Homogeneous Catalysis

Hydroformylation (oxo synthesis) is the conversion of alkenes into aldehydes with a mixture of carbon monoxide (CO) and hydrogen (H₂), which is called "Synthesis Gas". Large-scale oxo products are n-butanal ("C₄") in particular and its derivatives n-butanol and 2-ethyl hexanol ("2-EH"):

Here, low-valent rhodium (Rh) represents the established catalyst metal, which is applied via various compounds or precursors according to the processing systems (one phase or two phases, high or low pressure). It mainly replaced the former cobalt processes.

In principle, hydroformylations based on platinum (Pt) are considerable as well, e.g. in the combination of dihydrogen hexachloroplatinate(IV) with tin(II) chloride (SnCl₂).

For this Heraeus offers e.g.:

Carbonylations are conversions with carbon monoxide (CO) under formation of aldehydes, ketones, or carboxylic acids by inserting a C=O group.

The most important process on a large scale is the carbonylation of methanol to acetic acid ("Monsanto Process"):

Besides, there are other product routes, e.g. the manufacture of acetic anhydride from methyl acetate. All these processes are based on Rh in the presence of iodine-containing compounds. Recent methods are also based on iridium (Ir) with co-catalysts ("Cativa Process").

For the production of fine or pharmaceutical chemicals and specialties, some functional groups can be carbonylated by using various phosphorus-containing palladium (Pd) compounds, e.g. for the conversion of alkenes and alkynes into acrylates. The active species are Pd(0)-phosphane fragments: Therefore, there is a need of catalyst precursors of Pd(0) and Pd(II) respectively that contain phosphanes themselves or that are applied in situ along with phosphanes.

The Pd-based "Suzuki Coupling" reaction represents a method of linking an aryl halide ArX with an organoboron acid. Thus, in the presence of CO substituted aryl ketones Ar(CO)R can be synthesized.

Heraeus supplies you with e.g.:

Coupling reactions serve to link organic molecules or parts within a molecule mostly by forming carbon-carbon bonds ("C-C Coupling"). Such reactions are popular in the industries of pharmaceuticals, agrochemicals, fine chemicals, and specialties.

Similar to carbonylations, where - in fact - C-C coupling reactions also take place, these processes are based on Pd(0) and Pd(II) catalysts or their precursors. An example is the "Heck" reaction for the synthesis of vinyl derivatives from e.g. aryl, benzyl, and vinyl halides (RX) and a vinyl component as the reactant:

A large number of similar coupling reactions (according to "Suzuki", "Matsuda", "Stille", etc.) are based on this Pd chemistry. Important products are e.g. biphenyls for agrochemicals or liquid crystals.

Coupling reactions of dienes can also be performed with rhodium or even with ruthenium. A technical Rh-based process is the reaction of ethene with butadiene forming hexa-1,4-diene. The coupling of dienes is possible, too.

Heraeus is your partner for coupling catalysis with e.g.:

Also some oxidations can be homogeneously carried out on a large scale with precious metals. The best-known case is the "Hoechst-Wacker" process: The synthesis of acetaldehyde from ethene and oxygen in the presence of the catalyst system Pd/Cu (in aqueous, chloride-containing solutions):

Thus, other products can be obtained by varying the solvent, the starting material, or the process parameters (e.g. acetic anhydride and butane-2-one respectively from but-1-ene, or allyl acetate from propene).

In the fields of fine and pharmaceutical chemicals, 1,2-dihydroxylations of alkenes with Os in the form of osmium(VIII) oxide or potassium tetrahydroxodioxoosmate(VI) are important. Thus cis-1,2-diols are effectively formed in an aqueous system.

Ruthenium(VIII) oxide, which is best generated in situ from Ru precursors and suitable oxidizing agents (e.g. hydrogen peroxide), can cleave alkenes into carboxylic acids or oxidize secondary alcohols to ketones. In the presence of oxidizing agents, the oxidation of alcohols is also feasible by using Pd.

Heraeus offers you for oxidations e.g.:

• Ruthenium acetate

Hydrogenations are reactions of unsaturated molecules with hydrogen (H₂). Precious metal compounds of rhodium, ruthenium, or iridium rank with the most effective homogeneous hydrogenation catalysts because of their outstanding selectivities.

Catalysts for hydrogenations are often equivalent to those for hydroformylations, where the reactants H₂ and CO are applied.

Well-known are especiallychlorotris(triphenylphosphane)rhodium(I) ("Wilkinson's Catalyst") for the cis-hydrogenation of C=C's, and dichlorotris(triphenylphosphane)ruthenium(II) mainly for the hydrogenation of terminal C=C's.

Besides, C=O's, C=N's, and alkynes can be hydrogenated. Ruthenium in particular has an affinity for C=O bonds. Hydrogenations of imine groups could effectively be managed with iridium. On the basis of homogeneous ruthenium catalysts, ring hydrogenations are feasible, too.

Hydrogenations lead to chiral centres in prochiral molecules. Like right and left hands, "chiral" molecules of the same constitution (empirical formula, structure) can coincide only with their mirror-images. Chirality is extraordinarily important to modern agents in the field of life science, where almost just one chiral variant is active to a specific purpose.

Such "asymmetric hydrogenations" are feasible in a very effective way by using precious metal precursors along with chiral ligands. Heraeus offers a broad range of such precursors relevant to industry, mostly organometallics.

Heraeus is your partner in the field of hydrogenations with e.g.:

• Carbonylchlorobis(triphenylphosphane)rhodium(I), [RhCl(CO)(PPh₃)₂]

• Dichlorotris(triphenylphosphane)ruthenium(II), [RuCl₂(PPh₃)₃]

Hydrosilations (otherwise "hydrosilylations") represent reactions to build up higher-molecular organosilicon compounds (silanes, siloxanes), and thus they are the basis of manufacturing silicones. Today silicone products are found all over the dental, automotive, building, polymer, or paper industries.

From the chemical point of view, hydrosilation is the addition of a silicon-hydrogen compound to an unsaturated organic molecule, for example:

Platinum is the most effective metal for this homogeneously catalytic reaction. According to the purpose, it is mainly applied as "Speier's Catalyst", i.e. dihydrogen hexachloroplatinate(IV) hydrate ("CPA"), or in the form of "Karstedt's Catalyst". This means Pt(0) stabilized with, and dissolved in unsaturated organosiloxanes, e.g. divinyl tetramethyl disiloxane ("DVTMDS").

In special cases rhodium as well as palladium may serve as hydrosilation catalysts.

Heraeus represents one of the most important partners to silicone industry for this type of homogeneous catalysis. Among e.g. the following standard catalysts and precursors, we offer customized manufacturing of catalyst solutions ("Karstedt" types) on the basis of secrecy agreements:

• Platinum(II) chloride, PtCl₂

• cis-Diamminedichloroplatinum(II) ("Cisplatin"), cis-[PtCl₂(NH₃)₂]