Industrial processes homogeneous transition metal catalysts

PIONEERING INDUSTRIAL PROCESSES USING HOMOGENEOUS TRANSITION METAL CATALYSTS... 

Homogeneous transition metal catalysts are used in such industrial processes as ... 

Catalysis by organometallic compounds is based on activation of the substrates by coordinating it to the metal, which lowers the activation energy of the reaction between substrates. As in other types of catalysis the use of a homogeneous catalyst in a reaction provides a new pathway, because the reactants interact with the metallic complex first. Homogeneous transition metal catalysts are increasingly being applied in industrial processes to obtain bulk chemicals, fine chemicals and polymers. 

Hydroformylation, the addition of H and CHO to an olefinic double bond, is the oldest and largest industrial process that involves homogeneous transition-metal catalysts. The original catalyst was derived from Co2(CO)g. Later, phosphine modification of the system was introduced to afford better product selectivity and lower operating pressures. Still later, related Rh systems were introduced. ... 

In the sixties of past century, a few patents issued to Bergbau Chemie [5,48,49] and to Mobil Oil [50-52], respectively described the use of CFPs as supports for catalytically active metal nanoclusters and as carriers for heterogenized metal complexes of catalytic relevance. For the latter catalysts the term hybrid phase catalysts later came into use [53,54], At that time coordination chemistry and organo-transition metal chemistry were in full development. Homogeneous transition metal catalysis was expected to grow in industrial relevance [54], but catalyst separation was generally a major problem for continuous processing. That is why the concept of hybrid catalysis became very popular in a short time [55]. 

Future trends in reduction of substituted nitrobenzenes will probably be based on novel catalysts. Homogenous transition metal (ruthenium and rhodium) catalysts offer routes to chemospecific reduction of aromatic nitro groups16. Novel catalytic methods involving combinatorial chemistry may offer pathways to new industrial hydrogenation processes, where selective reduction is desired. A number of solution- and solid-phase C /Mo0 redox couple reductions of substituted nitroarenes to the corresponding anilines have been proposed17. 

In homogeneous transition-metal catalysis, separation and recycling of the catalyst are of the greatest importance. This is especially true for industrial processes involving noble metals. 

Hydroformylation or oxosynthesis is a well-known homogeneous, transition metal catalyzed reaction which has known considerable and continuous development since its discovery by Otto Roelen in the laboratories of Ruhrchemie AG in 1938 [1], This reaction, which can be considered as the addition of a formyl group and hydrogen to a double bond, has been successfully applied in the industrial context by using two basic processes the homogeneous process where the rhodium or cobalt catalyst and the substrate are in the same phase (Shell, UCC, BASF, RCH processes) [2] and the aqueous/organic biphasic process where the water-soluble rhodium catalyst and the organic compounds are in two different phases (Ruhr-chemie/Rhone-Poulenc process) [3]. 

A great variety of homogeneous catalysts are known metal complexes and ions, Bronsted and Lewis acid, enzymes. Homogeneous transition metals are used in several industrial processes, a few of them are given below... 

The use of catalysts in wet air oxidation (indicated with the acronyms CWAO or WACO) has already been implemented in various industrial processes (see Table 10.6), but in the form of homogeneous transition metals salts which favors the redox activation of oxygen. Two examples of industrial processes using solid catalysts are ... 

An example is the rhodium catalyzed hydroformylation reaction, which is an industrially important homogenous catalytic process [3]. In contrast, it is amazing that such an important transition-metal catalyzed C/C bond-forming process has been employed only rarely in organic synthesis [4]. Part of the reason stems from the difficulty in controlling stereoselectivity. Even though some recently developed chiral rhodium catalysts allow for enantio- and diastereoselective hydroformylation of certain specific classes of alkenes [5, 6], only little is known about the diastereoselective hydroformylation of acyclic olefins [7, 8]. 

---