A Novel, General Method for the Construction of C-Si Bonds by an Earth-Abundant Metal Catalyst

Citation

Betz, Kerry Nicole (2015) A Novel, General Method for the Construction of C-Si Bonds by an Earth-Abundant Metal Catalyst. Senior thesis (Major), California Institute of Technology. doi:10.7907/Z9FT8HZ9. https://resolver.caltech.edu/CaltechTHESIS:12162015-163246183

Abstract

Compounds containing carbon-silicon (C-Si) bonds are of great interest in numerous fields, including but not limited to synthetic chemistry, organic electronics, pharmaceutical chemistry, nuclear medicine, and complex molecule synthesis. Compounds that contain C-Si bonds display useful physicochemical properties, and the C-Si bond can readily be converted into other desirable functional groups. Current methods for the creation of C-Si bonds are somewhat limited, requiring either stoichiometric pyrophoric organometallic species or highly expensive, fine-tuned precious-metal catalysts; both methods have significant limitations in terms of applicability and scope. A novel and general catalytic approach to C-Si bond construction avoiding such limitations has been developed. Herein is disclosed a new method of cross-dehydrogenative heteroaromatic C-H functionalization catalyzed by certain Earth-abundant alkali metal species that is able to access all hybridizations of carbon: sp³, sp², and sp -hybridized carbons are all silylated in good yield under different conditions; prior to the discovery of this method, no known chemistry for C-Si bond construction was capable of accessing all hybridizations of carbon. Aromatic compounds, including heterocycles and oxygen-substituted arenes; benzylic sp³-hybridized carbons; and terminal alkynes, are directly silylated by potassium and sodium bases using hydrosilanes as the Si source, furnishing the silylated product in a single step. The overall catalysis is highly efficient: it proceeds under mild conditions, in the absence of hydrogen acceptors or other additives, and liberates dihydrogen as the sole byproduct; no competing hydrosilylation is observed. The scope of the method is broad, enabling the direct silylation of aromatic and aliphatic substrates in the presence of a wide array of valuable functional groups. Substrate classes such as nitrogen heterocycles that are challenging to activate with known transition metal catalysis strategies are functionalized in good yields by this Earth-abundant metal catalysis. Facile scalability, low cost, and excellent scope make this an attractive method for either large scale synthesis of versatile building blocks or late-stage functionalization of advanced intermediates and lead compounds. Turn-over numbers (TONs) of nearly 100 are achieved, demonstrating the remarkably high, albeit unanticipated efficiency and activity of the catalysis. The derived products readily engage in versatile transformations enabling new synthetic strategies for molecular diversification, and are useful in their own right in pharmaceutical and materials science applications.

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