Rhodium phosphine complex catalysts

The hydrogenation of various a/3-unsaturated acids in the presence of rhodium-phosphine complex catalysts whose ligands are chiral at both phosphorus and carbon gives saturated carboxylic acids with enantiomeric excesses up to 70%. The addition of carbon tetrachloride, catalysed by copper(ll) chloride, to (—)-men thy 1 acrylic and methacrylic esters, followed by hydrolysis, results in /3-tri-chloromethyl derivatives (6) having ca. 50% enantiomeric enrichment at the a-position. ... 

The processiag costs associated with separation and corrosion are stiU significant ia the low pressure process for the process to be economical, the efficiency of recovery and recycle of the rhodium must be very high. Consequently, researchers have continued to seek new ways to faciUtate the separation and confine the corrosion. Extensive research was done with rhodium phosphine complexes bonded to soHd supports, but the resulting catalysts were not sufficiently stable, as rhodium was leached iato the product solution (27,28). A mote successful solution to the engineering problem resulted from the apphcation of a two-phase Hquid-Hquid process (29). The catalyst is synthesized with polar -SO Na groups on the phenyl rings of the triphenylphosphine. 

Dialdehydes 8 have been converted to y-lactones 9 in the presence of a rhodium phosphine complex as catalyst. The example shown below demonstrates that this reaction works also with aldehydes that contain a-hydrogen atoms. 

Hydroboration of styrene derivatives has been extensively studied, and perhaps these are the best substrates to consider in a discussion of the efficiency and selectivity of the catalysts (Table 1-1). A neutral rhodium-phosphine complex... 

Rhodium also has been reported as a catalyst for [2+2+2] alkyne cycloaddition in water. Uozumi et al. explored the use of an amphiphilic resin-supported rhodium-phosphine complex as catalyst (Eq. 4.60). The immobilized rhodium catalyst was effective for the [2+2+2] cycloaddition of internal alkynes in water,113 although the yields of products were not satisfactory. 

Most hydroformylation investigations reported since 1960 have involved trialkyl or triarylphosphine complexes of cobalt and, more recently, of rhodium. Infrared studies of phosphine complex catalysts under reaction conditions as well as simple metal carbonyl systems have provided substantial information about the postulated mechanisms. Spectra of a cobalt 1-octene system at 250 atm pressure and 150°C (21) contained absorptions characteristic for the acyl intermediate C8H17COCo(CO)4 (2103 and 2002 cm-1) and Co2(CO)8. The amount of acyl species present under these steady-state conditions increased with a change in the CO/ H2 ratio in the order 3/1 > 1/1 > 1/3. This suggests that for this system under these conditions, hydrogenolysis of the acyl cobalt species is a rate-determining step. 

In 1997, Miyaura and co-workers reported the nonasymmetric version of 1,4-addition of aryl- and alkenylboronic acids to a,/ -unsaturated ketones using rhodium-phosphine complex as the catalyst.97 Later, Hayashi and Miyaura realized the asymmetric 1,4-addition with high catalytic activity and enantioselectivity.98 In the presence of ( y)-BINAP, the reaction of 2-cyclohexenone with 2.5 equiv. of phenylboronic acid gave (A)-3-phenylcyclohexanone with 97% ee (BINAP = 2,2 -bis (diphenylphosphino)-l,l -binaphthyl Scheme 29).99... 

In the hydrogenation of alkenes, rhodium-, ruthenium- and iridium-phosphine catalysts are typically used [2-4]. Rhodium-phosphine complexes, such as Wilkinson s catalyst, are effective for obtaining alkanes under atmospheric pres-... 

They constitute the first rhodium phosphine modified catalysts for such a selective linear hydroformylation of internal alkenes. The extraordinary high activity of 32 even places it among the most active diphosphines known. Since large steric differences in the catalyst complexes of these two ligands are not anticipated, the higher activity of 32 compared to 31 might be ascribed to very subtle bite angle effects or electronic characteristics of the phosphorus heterocycles. 

For instance, catalysis in liquid/liquid two phases is generally referred to as biphasic catalysis and has widened the practical scope of homogeneous catalysis the catalyst is present in one liquid phase, while reactants and products are present in the other liquid phase. Thus, the catalyst can be separated by simple phase separation. Celanese is operating a 300 000 t/a plant for propylene hydroformylation using a water-soluble rhodium phosphine complex in a biphasic mode of operation at the Ruhrchemie site in Oberhausen [142],... 

It has been reported that the chiral NMR shift reagent Eu(DPPM), represented by structure 19, catalyzes the Mukaiyama-type aldol condensation of a ketene silyl acetal with enantiose-lectivity of up to 48% ee (Scheme 8B1.13) [29-32]. The chiral alkoxyaluminum complex 20 [33] and the rhodium-phosphine complex 21 [34] under hydrogen atmosphere are also used in the asymmetric aldol reaction of ketene silyl acetals (Scheme 8BI. 14), although the catalyst TON is quite low for the former complex. 

Homogeneous hydrogenation in the fluorous phase has been so far reported only for a limited set of simple olefins (Richter et al., 1999, Rutherford et al., 1998), as exemplified with the neutral rhodium phosphine complex 18 as catalyst precursor (eq. 5.7). Isomerization of the substrate 1-dodecene (17a) was observed as a competing side reaction under the reaction conditions. The catalyst formed from 18 could be recycled using a typical FBS protocol, but deactivation under formation of metal deposits limited the catalyst lifetime. 

Fell, B., Schobben, C. and Papadogianakis, G. (1995) Hydroformylation of homologous C0-alkenecarboxylate esters with water soluble rhodium carbonyl/tertiary phosphine complex catalyst systems. J. Mol. Catal. A Chem., 101, 179. 

Discrete Chiral Rhodium Phosphine Complexes as Catalysts for Asymmetric Hydrosilation of Ketones... 

Most of the asymmetric homogeneous hydrogenations reported to date have used rhodium-phosphine complexes as catalysts. In a majority of these cases, it has been assumed that the active catalysts are similar to the well-studied... 

Many metal complexes catalyze the hydroboration. A neutral rhodium-phosphine complex RhCl(PPh3)3 is the most studied catalyst for the hydroboration of alkenes, but the complex is unfortunately highly sensitive to air. Thus, handling the catalyst under argon or in air resulted in different regioselectivity. The in situ preparation of the catalyst... 

Butadiene and ethylene are codimerized with a soluble rhodium-phosphine complex as the catalyst. Very little has been reported on the mechanistic evidence for this reaction. However, a catalytic cycle as shown in Fig. 7.9 involving a rhodium hydride seems likely. Reducing rhodium trichloride with ethanol in the presence of a tertiary phosphine generates the hydride complex 7.32. The 1,4-hydride attack on the coordinated butadiene gives an rf-allyl complex. This is shown by the conversion of 7.33 to 7.34. Ethylene coordination to 7.34 produces 7.35. 

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