Transition Metal Catalysts

Sample transition metals (iron, silver, irridium, rhodium, palladium, & nickel) in transition metal catalysts.

The field of catalysis is a wide and diverse field that attempts to emulate the refined function of enzymes, nature′s own catalysts. Transition metal catalysts have the capability to easily lend or take electrons from other molecules, making them excellent catalysts. One attractive feature of catalysis is that the catalytic species is not consumed during the chemical transformation. Catalysis by metals can be further subdivided into heterogeneous metal catalysis or homogeneous metal catalysis. Within the field of transition metals chemistry, there are several classes of transformations that have become prevalent in synthetic, and increasingly non-synthetic, chemistry. These methods are named after the laboratories from which they were developed and include but are not limited to: Stille, Buchwald–Hartwig, Negishi, Heck, Miyaura–Suzuki, and Sonogashira.

We supply a large variety of catalysts and metals that are of increasing importance to synthetic organic chemists. Our extensive portfolio of transition metal catalysts covers the majority of the transition metal block. Some of the more prominent metal catalysts are described below.



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Titanium Catalysts

We offer titanium complexes with a variety of organic ligands to form useful titanium catalysts for organic synthesis. For example, CpTiCl3 has been employed as an effective titanium catalyst for room-temperature heterocycle annulation reactions. The conversion of electron-deficient olefins to diastereomerically pure 7-hydroxynorbornenes and methyl acrylates to highly substituted norbornene derivatives employs titanocene dichloride and bis(methylcyclopentadienyl)titanium dichloride as the titanium catalysts.

Vanadium catalysis is the second largest application for vanadium after its use as an additive to improve steel production. A vanadium catalyst can effectively activate peroxides and selectively oxidize substrates like bromides, sulfides and alkenes. These catalysts have been shown to effectively transfer oxygen atoms to a substrate that is synthetically useful for obtaining valuable oxidized molecules on a large-scale reaction with a high degree of selectivity. Additionally, vanadium catalysts are efficient catalysts for olefin polymerization. Vanadium oxides can be applied in the emissions standards for vehicles and the desulfurization of crude oil. Moreover, the use of ecological oxidants, e.g., hydrogen and alkyl hydroperoxide, significantly increases the potential application of vanadium catalysts at an industrial level.

Iron and iron compounds are widely distributed in nature and can function as reagents or catalysts. For example, ferric chloride and bromide have long been used as Lewis acid iron catalysts in the classic electrophilic aromatic substitution reaction. Iron complexes with organic ligands are of particular interest and can serve as environmentally friendly Fe catalysts for a host of transformations. Illustrating this point is the very useful role that iron catalysis plays in the timely study of the ammonia–borane dehydrogenation process, since ammonia–borane (NH3:BH3, AB) is important as a hydrogen-storage material.

Being both economical and ecological, cobalt catalysts have attracted intense interest for cross-coupling. Cobalt catalysts are highly active reagents, extensively applied in the efficient and selective synthesis of pharmaceuticals, natural products, and new materials. These catalysts have been shown to have a higher reactivity for various carbon–carbon (C–C) bond formations. Cobalt catalysis with cobalt salts features good functional group tolerance, mild reaction conditions, and high chemoselectivity in comparison to palladium and nickel, the most commonly used catalysts for metal-catalyzed cross-coupling. A wide range of novel cobalt catalysis reactions, mediated by a variety of organometallic reagents with vinyl, alkyl or aryl halides, are possible.

Nickel catalysis plays a central role in many synthetic transformations ranging from cross coupling reactions in which carbon–carbon bonds are formed, to the reduction of electron-rich carbon bonds with raney nickel catalysts. These nickel catalysts span a range of oxidation states: Nickel (0), nickel (II), nickel (III) and nickel (IV). The types of Ni catalysts available for immediate purchase are aluminum nickel (Al Ni) alloys, ammonium nickel hydrates, Ni COD, Ni halides (chlorides, bromides, fluorides and iodides), Ni cyclopentadienyls, nickel metal, nickel acacs, and Raney Nickel catalysts that are products of W.R. Grace and Company.

Copper catalysts are useful for milder reaction conditions and show excellent yields, however the chemical reactions are slow and require high temperatures. Among transition-metal mediated reactions to form carbon–carbon bonds and carbon–heteroatom bonds, copper catalysis is utilized in Ullmann reactions, Diels–Alder reactions, ring expansions, Castro–Stevens coupling, the Kharasch–Sosnovsky reaction, and a notable variant of the Huisgen 1,3-dipolar cycloaddition utilizing a Cu(I) catalyst developed independently by Meldal and Sharpless. This so-called Copper(I)-catalyzed Azide–Alkyne Cycloaddition (CuAAC) gives rise to a triazole from a terminal alkyne and an azide.

The catalysis of carbon–carbon bonds and carbon–heteroatom bonds is central to synthetic chemistry and the synthesis of pharmacological, material, and biological compounds. Organic solvents and ligands as additives for copper-catalyzed cross-coupling reactions can improve reaction yields and utilize milder conditions. We provide efficient copper catalysts and precatalysts as well as copper-containing Metal Organic Framework (MOF) components.

Zinc catalysis finds wide applicability in synthetic chemistry and organic synthesis. A zinc chloride catalyst, acting as a moderate-strength Lewis acid, can catalyze the Fischer Indole synthesis to convert aryl hydrazones to indoles, and the Friedel–Crafts Acylation to produce monoacylated products from arenes and acyl chlorides. In addition to ZnCl2, a zinc oxide catalyst can be useful in a variety of catalytic conversions. We offer additional zinc catalysts, such as various zinc halides, that catalyze stereospecific and regioselective reactions. In addition to the catalytic properties of our zinc compounds, they find applications in material science in chemiluminescent quantum dots and nanomaterials. Our zinc compounds may also be used as starting materials in the preparation of organozinc reagents used in Negishi coupling.

The zirconium-catalyzed asymmetric carboalumination (ZACA) reaction, which was developed by Nobel laureate Ei-ichi Negishi, is perhaps one of the best-known examples of common applications of a zirconium catalyst. The ZACA reaction provides a means for chiral functionalization of alkenes with organoaluminum agents, catalyzed by a chiral bis(indenyl)zirconium catalyst. Another notable zirconium catalyst is zirconium dioxide or zirconia. The list of applications of zirconia catalyst in heterogeneous catalysis is rapidly growing. Some of the applications include: decomposition of nitric oxide, reduction of carboxylic acid to aldehydes, selective dehydration of secondary alcohols to terminal alkenes, and hydrogenation of carbon monoxide to isobutane.

Selective oxidative transformations of various functional groups with environmentally friendly and easily accessible oxidants can be readily achieved with the use of a proper ruthenium catalyst. Ruthenium catalysis can be a very powerful tool in synthetic chemistry for selective catalysis of oxidative transformations such as: asymmetric epoxidation of alkenes, generation of dioxygen species, dihydroxylation of olefins, and oxidative dehydrogenation of alcohols.

Ruthenium catalysts are also widely employed in metathesis reactions, with Grubbs′ catalysts being the most well-known in the field of olefin metathesis. The wide popularity of Grubb′s catalysts can be explained by their high tolerance of various functional groups, and their high stability in the air and a plethora of solvents.

Rhodium catalysts have been shown to be suitable promoters for the activation of carbon–hydrogen(C–H) bonds, which has emerged as a challenging and attractive tool for catalysis. Rhodium catalysis finds increasing interest in the catalytic dehydrogenative cross-coupling, allowing elegant C–C bond construction. Although palladium has been the metal of choice for most examples, Rh catalysts can be suitable promoters for this activation. By using rhodium catalysts, access is gained to important couplings, such as aryl–aryl, aryl–alkene, and alkene–alkene, as viable routes to valuable organic frameworks.

The ability to fine-tune the reaction conditions (temperature, solvents, ligands, bases and other additives) of palladium catalysts makes palladium catalysis an extremely versatile tool in organic chemical synthesis. Furthermore, palladium catalysts have a very high tolerance of various functional groups and are often able to provide excellent stereo- and regiospecificity, which helps to avoid the need for the introduction of protecting groups. This highly versatile group of catalysts is known for carbon bond forming reactions (primarily C–C, C–O, C–N and C–F), such as: Heck coupling, Suzuki coupling, Stille coupling, Hiyama coupling, Sonogashira coupling, Negishi coupling, and Buchwald–Hartwig amination, among others.

In heterogeneous catalysis, palladium catalysts, such as the Lindlar catalyst (or Lindlar′s Palladium), are highly efficient at facilitating selective hydrogenations, which include the conversion of triple bonds to cis-double bonds, monohydrogenation of polyolefins, and hydrogenation of azides to amines.

We welcome you to review our extensive offering of highly versatile homogeneous and heterogeneous palladium catalysts. For even greater convenience in purification and post-reaction cleanup, we have also included a selection of supported Pd catalysts, as well as a full line of recyclable and immobilized Pd Encat® catalysts that are suitable for various bond-formation and hydrogenation/reduction reactions.

Our portfolio has a wide variety of high-quality silver catalysts for transition-metal catalysis in organic synthesis. Silver catalysis is commonly used due to the high oxidation power of silver complexes and high oxidation potentials, additionally serving as silver activators enhancing the electronegativity of other catalysts, such as gold. Organic and inorganic synthesis benefits from the stoichiometric oxidation potential of silver compounds. Homogeneous silver-catalyzed organic transformations highlight the unique redox chemistry of silver, capable of catalyzing reactions with high stereo- and regioselectivity. Silver catalysts mediate both efficient intermolecular as well as intramolecular bond formations. Heterogeneous processes involving silver catalysis include NOx reduction and catalytic oxidation of carbon monoxide (CO) to carbon dioxide (CO2). Silver(I) salts can be used in several silver-catalyzed nucleophilic addition reactions and organic transformations. The high oxidation potential associated with Ag ions make silver catalysis, complexes, and ligands significant in chemical synthesis.

We provide efficient platinum catalysts, e.g., platinum dioxide, also called Adams′ catalyst, used for the hydrogenation of various functional groups and dehydrogenation in organic synthesis. Platinum black, the active Pt catalyst, is formed during the reaction. Utilizing platinum catalysis on alkynes results in syn-addition, forming a cis-alkene. Two of the most important transformations using platinum catalysts include the hydrogenation of nitro compounds to amines and ketones to alcohols. Notably, reductions of alkenes can be performed with the Pt catalyst Adams′ catalyst in the presence of nitro groups without reducing the nitro group. Platinum catalysts are preferred over palladium catalysts to minimize hydrogenolysis when reducing nitro compounds to amines. This Pt catalyst is also used for the hydrogenolysis of phenyl phosphate esters, a reaction that does not occur with palladium catalysts.

Prior to the 1980s, gold was regarded as having little catalytic activity. Advancements, spearheaded by F. Dean Toste (University of California, Berkeley) and others, have propelled gold into the forefront of transition metal catalysis. In particular, phosphine-ligated gold(I) complexes have recently emerged as powerful C–C bond forming catalysts, capable of performing a variety of reactions under mild conditions. The list of useful C–C bond construction methods includes cyclopropanations, enyne isomerizations, Rautenstrauch rearrangements, ene reactions, and ring expansions. Typically, the catalyst system relies on a phosphine gold(I) chloride complex in combination with a silver salt co-catalyst to generate the active species in situ.

No matter what your organic or organometallic catalysis application, we have precisely the transition metal catalyst that you need.




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