Selectivity homogeneous catalysts

The first examples of an electrostatie attachment of POMs on solid supports are dated to the mid 1980. Baba et al. reported immobilization of heteropolyacids on the anion-exchange resin Amberlist-15 [68]. Later on, this type of the support was successfully used by Jacob s group to immobilize the Venturello complex P04[W0(02)2]4, well known as highly selective homogeneous catalyst for H202-based epoxidation of alkenes... 

Saville has developed rules for chemical reactions that can also be used to select homogeneous catalysts. Consider the four-center reaction... 

In future, a complete quantitative analysis on the basis of chemical reaction engineering principles of homogeneously catalyzed gas-liquid-liquid reactions is needed to improve known aqueous biphasic reactions as well as to find new, highly active and selective homogeneous catalysts for organic synthesis. 

Complexes 292 and 293 were used as highly active and selective homogeneous catalysts for the hydrogenation of cyclohexene to cyclohexane, of nor-bornenone to norbornanone, and of butanal to 1-butanol." Chirality can also be introduced by using a chiral (phosphanylalkyl)cyclopentadienyl ligand such as 38, the lithium salt of which has been treated... 

New and more selective homogeneous catalysts continue to be developed. Very few catalysts for the homogeneous reduction of aromatic compounds are known but this year two have been reported. The first is the readily prepared rhodium complex [Rh(r -C5Me5)Cl2]2 which will reduce benzene (50°C/50atm) in the presence of a base to cyclohexane " with this catalyst a high stereospecificity for all ci5-addition is observed. The other report" concerns the use of salicylaldehyde complexes of copper and nickel for the catalytic reduction of aromatic rings, but there is some doubt as to whether the active catalysts are homogeneous or not. 

During the search for highly selective homogeneous catalysts for the direct conversion of CO/H2 to ethylene glycol, methanol always comprises a significant coproduct, particularly at lower (500 bar ) operating pressures (see the next section). Indeed, with several related catalyst systems, most notably... 

The reaction of iodobenzene with acrylate is a good synthetic method for the cinnamate 17[7]. In the competitive reaction of acrylate with a mixture of 0-and /i-iodoanisoles (18 and 19), the o-methoxycinnamate 20 was obtained selectively owing to the molecular recognition by interlamellar montmorillonite ethylsilyldiphenylphosphine (L) as a heterogenized homogeneous catalyst used as a ligand[28]. 

EBHP is mixed with a catalyst solution and fed to a horizontal compartmentalized reactor where propylene is introduced into each compartment. The reactor operates at 95—130°C and 2500—4000 kPa (360—580 psi) for 1—2 h, and 5—7 mol propylene/1 mol EBHP are used for a 95—99% conversion of EBHP and a 92—96% selectivity to propylene oxide. The homogeneous catalyst is made from molybdenum, tungsten, or titanium and an organic acid, such as acetate, naphthenate, stearate, etc (170,173). Heterogeneous catalysts consist of titanium oxides on a siUca support (174—176). 

A review of industrial processes that employ homogeneous catalysts is by Jennings, ed. (Selected Developments in Catalysis, Blackwell Scientific, 1985). Some of those processes are ... 

Copper chromite 14) and barium-promoted copper chromite (75,/7) have been used for acid reductions but very high temperatures (300 C) are required. The necessary temperature is sufficiently higher than that required foresters to permit selective reduction of half-acid esters to the hydroxy acid 23). The reverse selectivity can be achieved by reduction over H Ru4 CO)a PBu3)4 at I00-200 C and 1500-3000 psig. This homogeneous catalyst will reduce acids and anhydrides, but not esters (2). 

The Institut Fran ais du Petrole has developed and commercialized a process, named Dimersol X, based on a homogeneous catalyst, which selectively produces dimers from butenes. The low-branching octenes produced are good starting materials for isononanol production. This process is catalyzed by a system based on a nickel(II) salt, soluble in a paraffinic hydrocarbon, activated with an alkylalumini-um chloride derivative directly inside the dimerization reactor. The reaction is sec-... 

The potential for the use of catalysis in support of sustainability is enormous [102, 103]. New heterogeneous and homogeneous catalysts for improved reaction selectivity, and catalyst activity and stabihty, are needed, for example, new catalytic materials with new carbon modifications for nanotubes, new polymers. 

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