# Lewis superacids for catalytic reductions of stronger element–oxygen double bonds with hydrosilanes

## TL;DR

New superacid catalysts efficiently reduce tough oxygen-containing compounds using silanes as hydrogen sources.

## Contribution

Discovery of (pinF)2Si·MeCN as a versatile and potent promoter for reducing strong element-oxygen double bonds.

## Key findings

- The silicon complex (pinF)2Si·MeCN outperformed other promoters in reducing phosphine oxides and amides.
- Lewis acid base adducts of 1·Me2NCHO and 2·Me2SO were synthesized and structurally analyzed.
- PhSiH3 and (EtO)3SiH served effectively as hydrogen sources in these reductions.

## Abstract

The main-group Lewis superacid complexes (pinF)2Si·MeCN (1·MeCN) and (pinF)2Ge·MeCN (2·MeCN) were successfully applied as promoters in the catalytic reduction of phosphine oxides (e.g., Me3PO, Bu3PO, and Ph3PO), a sulfoxide (i.e., Me2SO), and an amide (i.e., Me2NCHO) to furnish the respective phosphines, dimethyl sulfide, and trimethylamine using silanes (e.g., PhSiH3 and (EtO)3SiH) as hydrogen sources (pinF = perfluoropinacolato). These substrates target difficult to reduce representatives of oxo compounds in comparison with, for example, the ketones or aldehydes often targeted in such types of catalytic reductions. As benchmark promoters, we also studied B(C6F5)3 and HNTf2 as reference (soft) Lewis superacid and Brønsted superacid, respectively (Tf = SO2CF3). Among the combinations of (pre)catalyst, substrate, and reducing agent investigated, the silicon complex 1·MeCN turned out to be the most versatile system, being the by far most potent (DMSO) or just slightly underperforming (R3PO and DMF) promoter. Moreover, the hitherto undescribed Lewis acid base adducts 1·Me2NCHO and 2·Me2SO were synthesized, isolated, and structurally investigated using NMR spectroscopy and single-crystal XRD analysis.

Perfluoropinacolate complexes of Si and Ge possess Lewis superacid properties. They function as potent promoters in the reduction of highly stable P

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Created by potrace 1.16, written by Peter Selinger 2001-2019
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O, SO, and CO double bonds with PhSiH3 and (EtO)3SiH.