Phosphane-modified rhodium catalysts

A range of high-yielding quaternary selective hydroformylation reactions have been performed in the presence of a reactive phosphane-modified rhodium catalyst at... 

Various phosphane-modified rhodium catalysts were tested in the hydroformylation reaction of unsaturated esters. Pronounced temperature dependence was observed on the regioselectivity and catalytic activity for these reactions and under the appropriate conditions, it was possible to obtain preferentially either linear or quaternary products (Equations 7.6 and 7.7) [38]. 

Ligands affect not only catalyst activity, but also stereoselectivity. Thus, hydrovinylation of norbornene with ethene using phosphane modified allylnickel complexes gives exclusively the exo-vinyl product4,5. In the rhodium-catalyzed codimerization of ethene and butadiene, the ratio of cis- and trans- 1,4-hexadiene is dependent on the type of donor used as the addend6. 

A polymer-supported rhodium catalyst modified with Diop attached to non-cross-linked polystyrene, first used in the asymmetric hydroformylation of styrene, gives 95 % branched aldehyde, however with only 2% ee9. Further developments in the preparation and use of cross-linked polymers with attached chiral phosphane ligands (Diop, DIPHOL, BPPM) in rhodium- and platinum-catalyzed asymmetric hydroformylation have led to good to excellent results with respect to the asymmetric induction62-124 157,159 and arc described in Section 1.5.8 2.2.3.2. The results arc integrated in Table 4. 

High-pressure in situ ETIR and polymer matrix techniques were used to study the rhodium-catalyzed hydroformylation of 1-octene, 1-butene, propene, and ethene using Rh(acac)(CO)2 or Rh(acac)(CO)(PPh3) in a polyethylene matrix as the catalyst precursor. The acyl rhodium intermediates, RC(=0)Rh(C0)4 and RC(=0)Rh (CO)3(PPh3), were observed. It was found that the acyl rhodium tetracarbonyl intermediates easily react with ethene to form acyl rhodium tricarbonyl species RC(=0)Rh(C0)3(C2H4) [61]. Deuterioformylation of l-phenyl-l-(n-pyridyl)-ethenes in the presence of a phosphane-modified Rh4(CO)i2 as catalyst precursor was carried out at 100 bar of CO D2 = 1 1 and 80 °C at partial substrate conversion. On basis ofa direct NMR analysis of the crude reaction mixture, it was concluded that the branched alkyl rhodium intermediate is almost exclusively formed [62]. 

---