Highly Efficient Enantioselective Pauson-Khand Reactions

A Study of [Co2(alkyne)(binap)(CO)4] Complexes (BINAP=(1,1′‐Binaphthalene)‐2,2′‐diylbis(diphenylphosphine))

“…Reports by Pauson, [21] Brunner, [21,22] and Kerr [23] using the chiral phosphine glyphos (11) in the asymmetric PKR with external alkenes state that diastereomer interconversion of the [Co 2 (glyphos)-(alkyne)(CO) 5 ] complex takes place at elevated temperatures, thereby lowering the ee. Activation of the asymmetric dicobalt species possessing either chiral phosphines or chiral alkynes in the range of 0 8C to room temperature is achieved using an N-oxide, such as N-methylmorpholine N-oxide or trimethylamine N-oxide, and thus limits epimerization and allows for increased enantiomeric excesses.…”

“…Activation of the asymmetric dicobalt species possessing either chiral phosphines or chiral alkynes in the range of 0 8C to room temperature is achieved using an N-oxide, such as N-methylmorpholine N-oxide or trimethylamine N-oxide, and thus limits epimerization and allows for increased enantiomeric excesses. [19,23,24] Other literature reports note how the diastereomeric ratios of dicobaltcarbonyl-alkyne complexes containing bidentate phosphorus-sulfur ligands can be enriched through heating. For instance, heating a 1:1 isomer mixture of [Co 2 (chiral-PÀS)(3,3-dimethylbutyne)(CO) 4 ] in toluene at 90 8C for 2 h, followed by heating under CO at 80 8C for 66 h, lead to a final ratio of 2:1.…”

Ferrocenylalkynes as ligands in transition metal complexes

“…Complex 3 lost an additional Co 2 (CO) 6 in the substitution resulting in an alternative route to 8. Interestingly, it has been reported that only one of the CC bonds of 4,4Ј-dipyridylbutadiyne reacts with Cp 2 Mo 2 (CO) 4 , even in the presence of an excess of the metal complex.…”

An Enantiospecific Pauson-Khand Reaction

“…In recent years, emphasis has moved to developing catalytic and stereoselective methods for the reaction. Significant progress has been made by Livinghouse, 2 Krafft 3 and Gibson 4 with respect to catalytic systems, whereas Kerr, 5 Pericás 6 and Chung 7 have produced highly stereoselective reactions. In the latter examples, stereocontrol is normally induced by rendering the two cobalt atoms electronically dissimilar.…”