Lewis Superacids for Catalytic Reductions of Stronger Element Oxygen Double Bonds with Hydrosilanes

Abstract

The Main Group Lewis Superacid complexes (pinF)2Si∙MeCN (1∙MeCN) and (pinF)2Ge∙MeCN (2∙MeCN) were successfully applied as promotors in the catalytic reduction of phosphine oxides (e.g. Me3PO, Bu3PO, Ph3PO), sulfoxide (i.e. Me2SO), and amide (i.e. Me2NCHO) to furnish the respective phosphines, dimethyl sulfide, and trimethylamine using silanes (e.g. PhSiH3, (EtO)3SiH) as hydrogen sources (pinF = perfluoropinacolato). These substrates mark difficult to reduce representatives for oxo compounds in comparison to, for example, the ketones or aldehydes often targeted in such type of catalytic reductions. As benchmark promotors, we also studied B(C6F5)3 and HNTf2 as reference (soft) Lewis Superacid and Brønsted Superacid, respectively (Tf = SO2CF3). Under consideration of the investigated combinations of (pre)catalyst, substrate and reducing agent the silicon complex 1∙MeCN turned out as the most versatile system being the most potent (DMSO) or just slightly outperformed (R3PO, DMF) promotor. Moreover, the hitherto undescribed Lewis acid base adducts 1∙Me2NCHO and 2∙Me2SO were synthesized, isolated and structurally investigated by NMR spectroscopy and Single Crystal XRD Analysis