Ferrocenylphosphine-gold catalyst

Interestingly, the aldol-type condensation of tosyhnethyl isocyanide 15 with aldehydes is catalyzed by the silver(I)/ferrocenylphosphine 2c or 2e catalyst more selectively than it is catalyzed by the chiral gold catalyst (about 20% ee) under the standard reaction conditions (Scheme 5) [30]. Oxazoline 16 can be converted to optically active a-alkyl-P-(N-metylamino)ethanols by reduction with LiAlH4. 

Asymmetric aldol reactions of a-keto esters (R-CO-COOMe R = Me, iBu, Ph) with methyl isocyanoacetate or N,N-dimethyl-a-isocyanoacetamide in the presence of 1 mol% of a chiral ferrocenylphosphine-gold(I) catalyst proceed enantiose-lectively (up to 90% cc) to give the corresponding oxazolines, which can be converted into optically active j8-alkyl-j8-hydroxyaspartic acid derivatives [1197]. Dehydration of the intermediate formamide to the corresponding isocyanide is accomplished in 97% yield with phosphoryl chloride at room temperature within 2h. 

In 1986 Ito, Sawamura, and Hayashi [4] reported that gold(I) complexes prepared from cationic gold complex 1 and chiral ferrocenylphosphine ligands (2) bearing a tertiary amino group at the terminal position of a pendant chain are effective catalysts for asymmetric aldol reaction of... 

Ito and coworkers found that chiral ferrocenylphosphine-silver(I) complexes also catalyze the asymmetric aldol reaction of isocyanoacetate with aldehydes (Sch. 26) [51]. It is essential to keep the isocyanoacetate at a low concentration to obtain a product with high optical purity. They performed IR studies on the structures of gold(I) and silver(I) complexes with chiral ferrocenylphosphine 86a in the presence of methyl isocyanoacetate (27) and found significant differences between the iso-cyanoacetate-to-metal coordination numbers of these metal complexes (Sch. 27). The gold(I) complex has the tricoordinated structure 100, which results in high ee, whereas for the silver(I) complex there is an equilibrium between the tricoordinated structure 101 and the tetracoordinated structure 102, which results in low enantioselectivity. Slow addition of isocyanoacetate 27 to a solution of the silver(I) catalyst and aldehyde is effective in reducing the undesirable tetracoordinated species and results in high enantioselectivity. 

Tributylphosphine sulfide has been used as a co-catalyst with dicobalt octacarbonyl for the Pawson-Khand reaction. Thermolysis of a mixture of cadmium chloride and trioctylphosphine sulfide at 250 °C has been used as a route to the formation of nanocrystalline cadmium sulfide." A complex of triphenylphosphine sulfide with a silver-tungsten-iodine acceptor has been characterised by X-ray studies. Ferrocenylphosphine chalcogenides have attracted considerable interest as ligands. Complexes of the monophosphino-phosphine sulfide (269) with rhodium have been characterised." The disulfide (270) forms complexes with both gold(i) and gold(iii) acceptors," and a silver(i) complex of the diselenide (271) has been prepared. ... 

In 1986 Ito and Hayashi pioneered the use of Au(l) homogeneous catalysts in asymmetric organic synthesis. Thus, the chiral ferrocenylphosphine/Au(l) catalyst precursor (3.55/3.56) formed in situ, catalysed asymmetric aldol reactions of an isocyanoacetate with aldehydes to produce optically active substituted oxazolines with high enantio- and diastereoselectivity (Scheme 3.22). The author suggested that the use of gold is essential for the high selectivity, a silver or copper catalyst being much less selective. 

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