Complexes of the general formula [MoO2X2L2] (X=Cl, Br, Me; L2=bipy, bpym) have been prepared and fully characterized, including X‐ray crystallographic investigations of all six compounds. Additionally, the highly soluble complex [MoO2Cl2(4,4′‐bis(hexyl)‐2,2′‐bipyridine)] has been synthesized. The reaction of the complexes with tert‐butyl hydroperoxide (TBHP) is an equilibrium reaction, and leads to MoVI η1‐alkylperoxo complexes that selectively catalyze the epoxidation of olefins. Neither the Mo−X bonds nor the Mo−N bonds are cleaved during this reaction. These experimental results are supported by theoretical calculations, which show that the attack of TBHP at the Mo center through the X‐O‐N face is energetically favored and the TBHP hydrogen atom is transferred to a terminal oxygen of the Mo=O moiety. After the attack of the olefin on the Mo‐bound peroxo oxygen atom, epoxide and tert‐butyl alcohol are formed. The latter compound acts as a competitive inhibitor for the TBHP attack, and leads to a significant reduction in the catalytic activity with increasing reaction time.
[(Bisphosphine) RuCl 2 (1,2-diamine)] complexes are powerful catalysts in the asymmetric hydrogenation of unfunctionalized ketones. We sought to expand the scope and applicability of these complexes by exploring changes to the diamine structural motif. Via introduction of 1,3- and 1,4-diamines, the catalytic activity was significantly altered such that new classes of ketones could be considered for [(bisphosphine) RuCl 2 (diamine)] asymmetric hydrogenation.
The asymmetric reduction of carbonyl, C=O, groups for the production of enantiomerically pure secondary alcohols is a reaction of fundamental importance in modern synthetic chemistry. This reaction can be performed in a number of ways. Asymmetric chemocatalysis (1) and the often complementary
biocatalysis offer solutions to the stereoselective reduction of C=O groups. These two techniques have found wide industrial application (2). In the mid 1990s, two new ruthenium systems based on dihydrogen or transfer hydrogenation for asymmetric reduction of prochiral ketones were developed
by Professors Noyori and Ikariya. These systems enable catalytic asymmetric reduction to provide a route for the generation of enantiomerically pure secondary alcohols in a highly efficient, simple and economic way (3). This paper describes some robust and cost-effective chemocatalytic technology
for asymmetric ketone reduction, using ruthenium catalysts with diphosphine ligands.
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