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

Abstract 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.