Cobalt Catalyzed Enantio- and Regioselective Hydrosilation

Abstract

Enantioselective and regioselective cobalt-catalyzed hydrosilation has been scarcely reported. Although this transformation catalyzed with other transition metals such as iron or copper is well known, cobalt being an abundant and cheap transition metal makes having its catalyst as an option to expand the "toolbox" highly desirable. In addition, enantioselective and regioselective silyl products can serve as important building blocks for creating chiral synthetic products. For example, chiral silanes can be converted into chiral alcohols via Fleming–Tamao oxidation. To conduct this experiment, 2-vinylnaphlene was chosen as the model substrate and various conditions for the hydrosilation of diphenylsilane were investigated. A variety of cobalt catalysts was screened and uniquely, cobalt chloride triphenylphosphine was used offering a cobalt(I) complex. Then the optimal solvent for this reaction was found to be dioxane. With this information, we screened various chiral ligands. The conversion and the regioselectivity of the reaction were determined with proton 1H-NMR. The enantioselectivity was determined through an HPLC assay.In the study, we were able to perform hydrosilation targeting the Markovnikov product. enantioselectivity was achieved with the optimal ligands, albeit with mild regioselectivity. The implications of this finding show promise for using cobalt for an enantioselective and regioselective hydrosilation reaction. Further steps could be taken toward modifying the ligand to enhance conversion, regioselectivity, and enantioselectivity. In addition, various other substrates and silanes could be explored to improve the scope of this study.