A Tethered Ru–S Complex with an Axial Chiral Thiolate Ligand for Cooperative Si–H Bond Activation: Application to Enantioselective Imine Reduction

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An axial chiral version of the 2,6‐dimesitylphenyl group attached to sulfur is reported. Its multistep preparation starts from (S)‐binol, and the thiol group is established by a racemization‐free thermal Newman–Kwart rearrangement. The new chiral thiolate ligand decorated with one mesityl group is used in the synthesis of a tethered ruthenium chloride complex. Its spectroscopic characterization revealed solvent‐dependent epimerization at the ruthenium center. The major diastereomer is crystallographically characterized. Chloride abstraction with tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate (NaBArF4) yields the corresponding coordinatively unsaturated ruthenium complex with the Ru−S bond exposed. Si−H bond activation at this Ru−S bond proceeds in syn fashion but with moderate facial selectivity (d.r.=70:30), generating diastereomeric chiral‐at‐ruthenium hydrosilane adducts. Their application to catalytic imine hydrosilylation led to promising enantioinduction (40 % ee), thereby providing proof of concept for asymmetric catalysis involving cooperative Si−H bond activation.