The conventional homogeneous catalysts for the enantioselective hydrogenation or transfer hydrogenation of ketones are based on platinum metals and, in particular, ruthenium. This method provides valuable enantiopure alcohols for the fine chemical industries. This tutorial review summarizes recent successes in replacing expensive and toxic ruthenium in these catalysts with "greener" iron substitutes including my lab's recent progress in this area using iron complexes containing readily-prepared tetradentate ligands. It will enlighten chemists interested in homogeneous catalysis and asymmetric synthesis.
[Show abstract][Hide abstract] ABSTRACT: Asymmetric transfer hydrogenation (ATH) is frequently carried out in the azeotropic mixture of formic acid (F) and triethylamine (T), where the F/T molar ratio is 2.5. This study shows that the F/T ratio affects both the reduction rate and enantioselectivity, with the optimum ratio being 0.2 in the ATH of ketones with the Ru-TsDPEN catalyst. Under such conditions, a range of substrates have been reduced, affording high yields and good to excellent enantioselectivities. In comparison with the common azeotropic F-T system, the reduction is faster. This protocol improves both the classic azeotropic and the aqueous-formate system when using water-insoluble ketones.
Journal of Molecular Catalysis A Chemical 05/2012; 357:133–140. DOI:10.1016/j.molcata.2012.02.002 · 3.62 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nicht SiSi, vielmehr SiOSi: Dimethylformamid (DMF) dient als Sauerstoffquelle in der effizienten Umwandlung von tertiären Silanen (R3SiH; R3=Ph2Me, PhMe2, Et3) in Disiloxane R3SiOSiR3 in Gegenwart von [(η5-C5H5)Fe(CO)2CH3] (1) als Katalysator. Das Ergebnis widerspricht einer verwandten, kürzlich veröffentlichten Studie, in der über die Bildung von Disilanen berichtet wurde.
[Show abstract][Hide abstract] ABSTRACT: Not Si-Si, rather Si-O-Si: Dimethylformamide (DMF) acts as an oxygen source in the efficient transformation of tertiary silanes (R3SiH; R 3=Ph2Me, PhMe2, Et3) into disiloxanes R3Si-O-SiR3 in the presence of the catalyst [(η5-C5H5)Fe(CO)2CH 3] (1; see scheme). This result contradicts a recently published related study, in which the formation of disilanes is reported.
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