Organometallic catalytic

Nonaqueous Bases Nonaqueous Nucleophiles Organometallic Catalytic Reduction Acidic Reduction Basic or Neutral Reduction Hydride Reduction Lewis Acids Soft Acids Radical Addition Oxidizing Agents... 

Figure 4.1 Monsanto process, (a) The organometallic catalytic cycle CH3I and CO react to give CH3COI. (b) The organic catalytic cycle water and HI act as catalysts to generate acetic acid and CH3I from CH3COI and methanol.

The Monsanto carbonylation of methanol to acetic acid catalyzed by Rh/H is a well-understood example of an organometallic catalytic cycle and can act as a good model with well defined steps (shown schematically in Chapter 4, Section 4.2.4). The starting material is the square planar Rh(I) complex, [Rh(CO)2l2] which is easily accessible by reaction of rhodium trichloride in solution with CO in the presence of iodide. This undergoes oxidative addition with Mel very readily to give the methyl-Rh(III) complex [Rh(Me)(CO)2l3] as an unstable... 

This catalysis nicely displays the way in which the electronic and steric properties of the organometallic catalytic complexes contain the three-dimensional prescription code for the precise assembly of product molecules from substrate molecules. The results are another demonstration of the importance of ligand choice in homogeneous catalysis. In this particular instance, the choice of neutral... 

Figure 2.14 Concept of using ionic liquids (hosting organometallic catalytic complexes) supported on an alumina nano-membrane to develop novel systems that can combine catalysis and separation.

PG Aqueous Basic Nucleophilic Organometallic Catalytic Reduction 1 Elec. Red. ... 

Hydrogenation was one of the first organometallic catalytic reactions studied in aqueous solution and continues to attract interest. 

According to the general principles of asymmetric synthesis, chiral induction can be effected via substrate, reagent, or external (catalyst) control. Effective substrate control in the sense of induced diastereoselectivity requires a preformed stereogenic center within the substrate. For organometallic catalytic conversions a stereospecific reaction course and simple diastereoselectivity, as outlined above, is prerequisite. 

For the design of organometallic catalytic reactions, one can apply stereoelectronic effects that are specific to the metal centers, such as the trans-effect. An interesting manifestation of this effect in the Rh-catalyzed Claisen rearrangement of propargyl vinyl ethers (Figure 11.13) was found in the computational analysis of this process. ... 

We have seen that free-radical polymerization of ethylene leads to the formation of low-density polyethylene (LDPE). The reason for the low density of LDPE is the lack of crystallinity owing to branching in the polymer. Straight-chain polyethylene can be obtained from Ziegler-Natta polymerization, which involves the use of an organometallic catalytic system [1-5, 18-20]. 

G. Natta, an Italian chemist, made an extremely important extension of the use of Ziegler s catalytic system. He showed the utility of Ziegler cat-lysts for the room temperature pol)rmerization of propylene. Most importantly, however, Natta observed that the organometallic catalytic system, leads to the preparation of a stereoregular polymer. Thus, polypropylene can have three possible stereochemical orientations [1]. 

Green chemistry and atom economy are relatively new thrusts in the chemical industry worldwide their goals are well complemented by organometallic catalytic reactions. 

In the Friedel-Crafts realm, Lou and coworkers reported on the activity of Mg-phosphoric acid-based binary catalyst in the alkylation of free phenols via Michael addition of p,y-unsaturated a-ketoesters 25 [41], Despite the real structure of the binary organometallic catalytic species is still unknown, excellent levels of chemical and optical outcomes were achieved in the titled process (Scheme 5.24). To be mentioned that neither the BA nor MgF alone could promote the model reaction at any extents, proving the formation of a concertedly activated catalytic aggregate between the two acids. 

Thermodynamic stability of M—C bond in water has raised questions about lifetimes of intermediates in the aqueous organometallic catalytic cycles. From deuterium-labeling experiments (Eq. 6.3), Sinou and coworkers have concluded that the protonation of the M—C bond can occur readily. When the reduction of (Z)-acetamidocinnamic acid methyl ester was performed under hydrogen in a two-phase system (Et0Ac-D20) in the presence of the catalyst [Rh(cod)Cl]2- - TPPTS [tris-(OT-sulfonato-phenyl)phosphine], regioselective... 

As an alternative to the heterogenization of homogeneous catalysis, there are some proposals to realize a solid catalyst with an immobilized species in aqueous/organic media. This concept, a continuation of the SLPC as mainly published and highlighted by Scholten et al., consists of a thin film of catalytic material that resides on a high-surface-area support such as controlled-pore glass, silica, zeolites. Thus this concept of supported aqueous phase catalysis (SAPC) contains both a hydrophilic liquid and a hydrophilic organometallic catalytic complex on a solid support as shown in Fig. 12.15. "... 

An important area of application for indium(III) triflate is as a co-catalyst in other organometallic catalytic C-C bond forming reactions. The ruthenium-catalyzed three-component addition to form 1,5-diketones, reported by Trost, is a classic example (eq 21). The best catalyst employs a two-metal system composed of CpRu(COD)Cl and indium(III) triflate. The exact contribution of indium complex is unresolved although a part of it may be as a chloride scavenger. 

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