The coordination of the P-stereogenic and sterically demanding bisphosphine QuinoxP* to mu-alkyne dicobalt hexacarbonyl complexes was studied experimentally and computationally. 'Whereas the coordination occurred exclusively in a chelating fashion, the diastereoselectivity was highly substrate dependent. However, it could be explained from the computed structure and energies of the different coordination modes. The fluxional behavior of these complexes was also studied computationally. Their performance as catalysts for the Pauson-Khand reaction was explored, and outstanding reactivity was observed. Although the asymmetric induction was low to "moderate, the stereochemical outcome could be mechanistically rationalized. This report provides promising results in terms of reactivity and mechanistic understanding for further developments of highly active chiral catalysts for intermolecular Pauson Khand reactions.
Catalytic Pauson–Khand Reaction in Ethylene Glycol–Toluene: Activity, Selectivity, and Catalyst Recycling
作者:Xavier Verdaguer、Antoni Riera、Albert Cabré
DOI:10.1055/s-0037-1610441
日期:2018.10
additive in the catalytic Pauson–Khand reaction (PKR) is reported. In most cases both the yield and selectivity were enhanced compared to standard protocols. Moreover, the immiscibility of ethylene glycol in toluene allowed recycling of the catalyst (which remained mainly in the ethylene glycol). The recycling allowed catalyst loading to be reduced to only 3 mol%. A gram-scale reaction was also performed