Phosphane catalysts

Birkholz, M.-N., Dubrovina, N.V., Jiao, H., Michalik, D., Holz, J., Paciello, R., Breit, B. and Borner, A. (2007) Enantioselective hydrogenation with self assembling rhodium phosphane catalysts Influence of ligand structure and solvent. Chem.-Eur. J., 13, 5896-5907. 

An interesting case of an intramolecular dimerization reaction occurs on treatment of the ethylene-bridged MCP 12 with a nickel/phosphane catalyst system. The tricyclic dimer 13 is formed in 33% yield.The only obvious rationale for this reaction is a proximal ring cleavage occurring at one of the methylenecyclopropanes and subsequent addition to the alkene of the other. 

The basic structure 1 is structurally related to complexes of types 2 and 3 (Tab. 1.3). A comparison is of interest because of the marked differences in activity and selectivity of yhde catalysts 1, phosphane catalysts 2, and ris-[Ni(PO)2] bis(chelate) complexes 3. The yhde catalysts 1 are significantly more active and produce higher molecular weight products than corresponding phosphane catalysts 2. The bis(chelate) complexes 3 can be detected as polymerization-inactive decomposition products of 1 and 2, e.g. after completed ohgo- or polymerization. 

Bis(ylide)nickel catalysts are of high chemical variability and show superior performance in the activation of unsaturated substrates such as acetylene. The normalized polymerization activity in dimethyl sulfoxide (DMSO) of 500 mol polymerized acetylene per mol nickel (h aim) by far exceeds that of structurally related phosphane catalysts by a similar order of magnitude as observed in ethylene polymerizations (see Sections 1.2 and 1.3.1). To our knowledge this activity even exceeds that of all other nickel catalysts reported so far (Fig. 1.4). 

Figure 3.3 Catalysis with a fluorous phosphane catalyst (21) in a homogeneous hydrocarbon solvent. Because of the very different solubility of 21 in hot and cold octane, the catalyst can be quantitatively precipitated from the reaction mixture by simple cooling to —30°C (the lower scheme was re-drawn from Ref. [22]).

Fig. 10 Phosphane catalysts used in the catalytic hydrogenation of Z-a-acetamidocinnamic acid.

The reduction of 2- benzyl(methyl)amino]-l-[3-(benzyloxy)phenyl]ethanone was carried out with the same in situ rhodium/phosphane catalyst to give (S)-2-[benzyl(methyl)amino]-l-[3-(benzyl-oxy)phenyl]ethanol in 85 % ee44 (Table 6). This reaction constitutes the enantioselective step in a synthesis of (tf)-phenylephrine hydrochloride, another /1-receptor-stimulating agent having a chiral benzylic alcohol group44. 

Hydrogenation of 2-Acylamino-2-alkenoic Acids and Esters with Rhodium Phosphane Catalysts General Procedure20 ... 

The addition of 30% water by volume to acetone was found to create a simple polar-phase solvent system that produces 30-115% rate enhancements for the hydroformylation of 1 -hexene with a variety of monometallic rhodium phosphane catalysts, and a 265% rate increase for a dirhodium tetraphosphane catalyst possessing bridging and terminal carbonyl groups along with improved chemosdectivity to aldehyde products [31]. 

Hydroformylation of 1-hexene in supercritical carbon dioxide was investigated using a rhodium-phosphane catalyst tethered to a silica support. The performance of the tethered catalyst was compared with a homogeneous rhodium-phosphane... 

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