Leveraging Silyl-Palladium Cations for Catalytic C-O Bond Reduction and Functionalization

The pronounced electrophilicity of silylium ions has led to their deployment as potent Lewis acid catalysts. However, its ability to activate nearly any σ or π electron donor has limited its use as a general catalytic tool. Main-group Lewis acidic borane catalysts, such as B(C6F5)3, are able to polarize hydrosilane to perform a net silylium transfer. This method of polarization has been used in the selective functionalization of carbohydrate substrates. Critically, these catalysts lack the ability to perform elementary organometallic reactions, prompting the development of transition-metal systems that can transfer silylium to Lewis bases.Among the mechanisms used by transition-metal complexes for transferring silylium to Lewis bases are those that generate a low-valent metal nucleophile upon silyl ligand transfer. Historically, (CO)xM complexes have successfully employed this mechanism in the generation of metal-carbon bonds, with further functionalization readily achieved by CO ligand insertion. Developing methods that leverage metal-carbon bond formation beyond CO insertion is especially appealing for the continued development of these complexes. Chapter 2 describes methodology for the hydrosilylation of ketones employing catalytic quantities of silylpalladium cations. This methodology resulted in divergent product selectivity based on hydrosilane identity, with primary silanes favoring silyl ether formation, while secondary silanes favored alkane production. The mechanism of this selectivity difference was subsequently probed, with the primary difference attributed to a difference in their ability to transfer silylium to silyl ether products. Further studies revealed the presence of a bimetallic palladium system when secondary silanes were employed, suggesting the appearance of Pd0 in the catalytic cycle.