Homogeneous metal

Oxo Synthesis. Ad of the synthesis gas reactions discussed to this point are heterogeneous catalytic reactions. The oxo process (qv) is an example of an industriady important class of reactions cataly2ed by homogeneous metal complexes. In the oxo reaction, carbon monoxide and hydrogen add to an olefin to produce an aldehyde with one more carbon atom than the original olefin, eg, for propjiene ... 

The tert-huty hydroperoxide is then mixed with a catalyst solution to react with propylene. Some TBHP decomposes to TBA during this process step. The catalyst is typically an organometaHic that is soluble in the reaction mixture. The metal can be tungsten, vanadium, or molybdenum. Molybdenum complexes with naphthenates or carboxylates provide the best combination of selectivity and reactivity. Catalyst concentrations of 200—500 ppm in a solution of 55% TBHP and 45% TBA are typically used when water content is less than 0.5 wt %. The homogeneous metal catalyst must be removed from solution for disposal or recycle (137,157). Although heterogeneous catalysts can be employed, elution of some of the metal, particularly molybdenum, from the support surface occurs (158). References 159 and 160 discuss possible mechanisms for the catalytic epoxidation of olefins by hydroperoxides. 

Ail homogeneous metals without differences in potential between any points on their surfaces are subject to this type of general attack under some conditions. Uniform corrosion is usually characterized by a chemical or electrochemical attack over the entire exposed surface, Figure 4-423. Metal corrodes in an even... 

Such a broad range of classical elementary reactions of homogeneous catalysis with metal complexes, that can be facilitated by photons, make illumination of reaction solution a very useful instrument for substantial increase of the possibilities of homogeneous metal complex catalysis in organic synthesis. Particular examples of light-assisted syntheses will be given in section 3. 

The performance of the Sonogashira reaction is claimed to be the first example of a homogeneously metal-catalyzed reaction conducted in a micro reactor [120], Since the reaction involves multi-phase postprocessing which is needed for the separation of products and catalysts, continuous recycling technology is of interest for an efficient production process. Micro flow systems with micro mixers are one way to realize such processing. 

The reductive carbonylation has an advantage of low feedstock cost. A wide range of homogenous metal complexes have been tested for both reactions (1-16). The major drawback of the use of metal complex catalysts is the difficulty of catalyst recovery and purification of the reaction products (12). In addition, the gaseous reactants have to be dissolved in the alcohol/amine mixture in order to have an access to the catalyst. The reaction is limited by the solubility of the gaseous CO and 02 reactants in the liquid alcohol reactant (17). 

The great stability of the M=S and M-S-M moieties toward the elimination of S as H2S probably explains the lack of success of polynuclear species in assisting a catalytic reaction. The first example of hydrogenation of M=S to M(H)SH in a discrete homogeneous metal system was reported only in 1997 by Bergman and co-workers for [(Cp) 2TiS(pyridine)].231... 

The polymerization of olefins and di-olefins is one of the most important targets in polymer science. This review article describes recent progress in this field and deals with organo-transition metal complexes as polymerization catalysts. Recent developments in organometallic chemistry have prompted us to find a precise description of the mechanism of propagation, chain transfer, and termination steps in the homogeneously metal-assisted polymerization of olefins and diolefins. Thus, this development provides an idea for designing any catalyst systems that are of interest in industry. 

We review herein progress in microwave-assisted homogeneous metal catalysis in the liquid phase. Most of the work published in this field is, as the reader will see, associated with palladium chemistry, and this will, by necessity, also be reflected in the text. 

In broad terms there are three types of catalyst for transfer hydrogenation dehydrogenases heterogeneous and homogenous metal catalysts. Here, the first two are mentioned for completeness, and the main focus of this chapter will be asymmetric transfer hydrogenation with homogenous metal catalysts. 

Industrial interest in the application of enantioselective catalysts began in earnest during the mid-1960s when the first reports of successful enantioselective transformations with homogeneous metal complexes were published. Within a surprisingly short period, production processes for two small-scale products, L-dopa (hydrogenation) and cilostatin (cyclopropanation) were developed and implemented by... 

The seminal report of an asymmetric homogeneous metal-catalyzed reaction described the copper-catalyzed group-transfer reaction from a diazoester to an alkene, Eq. 3 (2). This article provided experimental verification of the intervention of copper carbenoid olefin complexes in the catalytic decomposition of diazo com-... 

Vacuum atomization is a commercial batch process)180 The development of vacuum atomization started in the mid 1960 s, concurrent with the development of inert gas atomization. In 1970, a patent for the vacuum atomization method was issued to Homogeneous Metals, Inc. Using vacuum atomization, this company routinely produces superalloy powders of fine size without great consumption of argon, giving powders free of inert gas filled porosity. Wentzell1 801 has made detailed description of this proprietary process. 

Some homogeneous metal catalysts have been examined in the production of acrolein from glycerol [20], However, considering all reaction components present, it is more likely that soluble acids, such as HC1 and CF3SO3H, are responsible for glycerol dehydration instead of Pt and Pd phosphine complexes. 

The reaction between alkenes and synthesis gas (syngas), an equimolar mixture of carbon monoxide and hydrogen, to form aldehydes was discovered in 1938 by Otto Roelen [1,2]. Originally called oxo-reaction , hydroformyla-tion is the term used today. This reflects the formal addition of formaldehyde to the olefinic double bond. Commercially, homogeneous metal complexes based on cobalt and rhodium are used as catalysts. With more than 10 million metric tons of oxo products per year, this reaction represents the most important use of homogeneous catalysis in the chemical industry. 

The prototypical C-C bond forming hydrogenation, hydroformylation combines basic feedstocks (a-olefins, carbon monoxide, and hydrogen) with perfect atom economy and accounts for the production of over 10 million metric tons of aldehyde annually, making it the largest volume application of homogeneous metal catalysis. 

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