title: 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.
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 115, 10623, Berlin, Germany.
authors.forename: Simon
authors.identifier: http://orcid.org/0000-0002-0841-6022
authors.initials: S
authors.lastname: Wübbolt
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 115, 10623, Berlin, Germany.
authors.forename: Modhu Sudan
authors.identifier: http://orcid.org/0000-0001-9647-2683
authors.initials: MS
authors.lastname: Maji
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 115, 10623, Berlin, Germany.
authors.forename: Elisabeth
authors.identifier: http://orcid.org/0000-0001-6098-1996
authors.initials: E
authors.lastname: Irran
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 115, 10623, Berlin, Germany.
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0002-1487-9218
authors.initials: M
authors.lastname: Oestreich
keywords: Lewis acids; Si-H bond activation; asymmetric catalysis; homogeneous catalysis; hydrosilylation