om7b00030_si_002.cif (29.38 kB)
Hidden Enantioselective Hydrogenation of N‑Silyl Enamines and Silyl Enol Ethers in Net CN and CO Hydrosilylations Catalyzed by Ru–S Complexes with One Monodentate Chiral Phosphine Ligand
dataset
posted on 2017-02-13, 17:22 authored by Susanne Bähr, Martin OestreichRuthenium thiolate
complexes with one chiral monodentate phosphine
ligand are applied to enantioselective hydrosilylation of enolizable
imines and ketones. The structural features of the catalyst exclude
the presence of more than one phosphine ligand at the ruthenium center
in the enantioselectivity-determining step. The enantiomeric excesses
obtained in these reduction reactions are moderate (up to 66% ee),
but the stereochemical outcome enables an experimental analysis of
the reaction pathways operative in this catalysis. A two-step sequence
consisting of successive N–Si/O–Si dehydrogenative coupling
and enamine/enol ether hydrogenation is the prevailing mechanism of
action. Both steps involve cooperative bond activation at the Ru–S
bond of the coordinatively unsaturated ruthenium complex: Si–H
bond activation in the dehydrogenative coupling and heterolytic H–H
splitting in the hydrogenation. Previously documented side reactions
such as deprotonation/protonation equilibria as well as competing
direct CN or CO hydrogenation have been excluded.
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phosphine ligandenantiomeric excessesstereochemical outcomereduction reactionshydrogenationbond activationside reactionsenantioselective hydrosilylationreaction pathwaysenantioselectivity-determining stepEnantioselective Hydrogenationenolizable iminesdehydrogenativeruthenium centerMonodentate Chiral Phosphine Ligand Ruthenium thiolate complexesSilyl Enol Etherschiral monodentate phosphine ligand