Phosphine-rhodium catalysts

This H-transfer reduction with sodium formate and employing catalysis by a water-soluble rhodium-phosphine catalyst yields dimethyl methylsuccinate [117]. 

Some general reviews on hydrogenation using transition metal complexes that have appeared within the last five years are listed (4-7), as well as general reviews on asymmetric hydrogenation (8-10) and some dealing specifically with chiral rhodium-phosphine catalysts (11-13). The topic of catalysis by supported transition metal complexes has also been well reviewed (6, 14-29), and reviews on molecular metal cluster systems, that include aspects of catalytic hydrogenations, have appeared (30-34). 

SHOP [Shell Higher Olefins Process] A process for producing a-olefins by oligomerizing ethylene, using a proprietary rhodium/phosphine catalyst. The a-olefins can then be iso-merized to internal olefins as required. Invented by W. Keim in the Institut fur Technische Chemie und Petrolchemie, Aachen, in the 1970s. The first plant was built in Geismar, LA, in 1979 the second in Stanlow, Cheshire, in 1982. Licensed worldwide by a consortium of Union Carbide, Davy-McKee, and Johnson Matthey. 

The other three studies in the literature also deal with the asymmetric hydroformylation of styrene and all three applied water soluble rhodium -phosphine catalysts (Scheme 4.9). BINAS (44), sulfonated BIPHLOPHOS (43), tetrasulfonated (R,R)-cyclobutane-DIOP (37, m=0) and tetrasulfonated (S,S)-BDPP (36, m=0) were applied as ligands of the rhodium catalyst prepared in situ from [Rh(acac)(CO)2] or [ Rh( Li-OMe)(COD) 2] and the phosphines. The results are summarized in Table 4.4. 

Rhodium-phosphine catalysts are unable to hydroformylate internal olefins, so much that in a mixture of butenes only the terminal isomer is transformed into valeraldehydes (see 4.1.1.2). This is a field still for using cobalt-based catalysts. Indeed, [Co2(CO)6(TPPTS)2] -i-lO TPPTS catalyzed the hydroformylation of 2-pentenes in a two-phase reaction with good yields (up to 70%, but typically between 10 and 20 %). The major products were 1-hexanal and 2-methylpentanal, and n/i selectivity up to 75/25 was observed (Scheme 4.12). The catalyst was recycled in four mns with an increase in activity (from 13 to 19 %), while the selectivity remained constant (n/i = 64/36). 

Using the catalyst system described above in combination with a rhodium phosphine catalyst Lebel reported the de novo synthesis of alkenes from alcohols [100]. They developed a one-pot process, avoiding the isolation and purification of the potentially instable aldehyde intermediate. They combined the oxidation of alcohols developed by Sigman [89] with their rhodium-catalyzed methylenation of carbonyl derivatives. The cascade process is compatible with primary and secondary aliphatic as well as benzyUc alcohols in good yields. They even added another reaction catalyzed by a NHC complex, the metathesis reaction, which has not been addressed in this review as there are many good reviews, which exclusively and in great depth describe all aspects of the reaction. 

Derivatives of the steroids androstene and pregnene have been transformed directly into A-acyl amino acids by an orthogonal catalysis procedure, utilizing [RhCl(nbd)]2 and Co2(CO)8 (Scheme 11). The rhodium phosphine catalyst (generated in situ in the presence of syn-gas and phosphine) affects hydroformylation of the internal olefin to generate aldehyde. In the presence of Co2(CO)8, A-acyl amino acids are obtained as the major products. An unstable amido alcohol intermediate, formed by reaction of the amide with aldehyde, is proposed to undergo cobalt-catalyzed GO insertion to yield the desired A-acyl amino acid. 

Myrcene and a-terpinene contain conjugated double bonds and are not as reactive as limonene and a-pinene. The product mixture is complex besides the hydrogenated products and the alcohols, undefined high boiling point products also occur [42]. The two conjugated terpenes were also studied with rhodium phosphine catalysts. Within 7 h, 96% of a-terpinene reacts to aldehydes with high selectivity for the product shown in Scheme 13 [43]. 

As described above, the rhodium-phosphine catalysts used extensively by the Horner and the Monsanto groups contained phosphines that were asymmetric... 

FIGURE 31 A noncovalently silica-immobilized rhodium phosphine catalyst (720). 

After polymerization processes, one of the most important aqueous phase reactions to be performed on an industrial scale is the Rhone-Poulenc hydro-formylation process that utilizes a water soluble rhodium phosphine catalyst. This process will be discussed in more detail in Chapter 10. The success of this process has led to many exciting results in metal catalysed aqueous phase chemistry. Additionally, amazing advances have been made where reactions that are typically considered unsuited to the presence of moisture, e.g. Grignard-type chemistry, can be performed in water. 

Rhodium-phosphine complexes are usually active and effective in the asymmetric hydrosilylation of olefins, ketones, and aldehydes, allowing for the virtual synthesis of optically active alkoxysilanes and organic compounds of high purity. Chiral rhodium-phosphine catalysts predominate in the hydrosilylation of pro-chiral ketones. This subject has been comprehensively reviewed by several authors who have made major contributions to this field [52-54]. A mechanism for the hydrosilylation of carbonyl groups involving the introduction of asymmetry is shown in Scheme 3 [55]. 

The solution to this problem has been to attach these catalysts to polymer supports. The ideal polymer-bound catalyst must satisfy a formidable list of requirements. It should be easily prepared from low cost materials. The support must be compatible with the solvent system employed, and be chemically and thermally stable under the reaction conditions. The catalyst should show minimal losses in reaction rate or selectivity when bound to the support, and should be able to be recycled many times without loss of activity. Finally, the interactions between the catalytic site and the support must be either negligible or beneficial. The development of polymer supported rhodium-phosphine catalysts for the asymmetric hydrogenation of amino acid precursors illustrates the incremental process which has led to supports which approach the ideal support. 

The rhodium-phosphine catalyst [Rh(T)-L] was prepared from [ RhCl(NBD) 2] and the chelating bisphosphines 141 and 142 [59] following chloride removal with silver triflate. In fact, the two systems on Scheme 3.52 and 3.53 could be mn together, with the net result of hydrogenation of ketones by molecular hydrogen. The same rhodium-phosphine complex catalyzed the direct hydrogenation of flavin mononucleotide to dihydroflavin mononucleotide [59],... 

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