Online

Reuter, Matthew Bryan

Chemistry

2023

Ph. D.

Silicon-nitrogen heterodehydrocoupling has emerged as a versatile method to couple silanes and amines through catalysis. A diverse range of small molecules, polymers, and materials with Si-N bonds are now accessible through heterodehydrocoupling, which has greatly improved upon longstanding, stoichiometric transformations. However, challenges and limitations are clearly present in this underdeveloped field. Highly active systems are dominated by designer compounds and rare metals. Catalyst activity is inconsistent across the periodic table. Critically, a straightforward methodology has yet to be developed where silanes and amines are coupled under mild conditions with readily accessible precatalysts. The commercially available iron dimer Cp2(CO)4Fe2 emerged as a competent catalyst for Si-N heterodehydrocoupling under visible-light irradiation. Reactions between either primary or secondary amines with silanes demonstrated variable efficiency, which afforded mixtures of mono- and bis(aminosilane) products in conversions between 20-100%. Analogous reactions between alcohols and silanes produced silyl ethers quantitively using Cp2(CO)4Fe2. Mechanistic insight unveiled the production of several intermediates, such as Cp(CO)2FeSiR3 and Cp(CO)2FeH. Nucleophilic Cp(CO)2FeNR2 or Cp(CO)2FeOR were proposed as the bond-forming intermediates, which was highlighted by the increased reactivity of alcohols over amines in this catalysis. Notably, the greatest challenge of this work was the poor activation of Cp2(CO)4Fe2 under irradiation, which launched an expedition into catalyst derivatization. In the course of studying iron-catalyzed heterodehydrocoupling, commercially available organolithium reagents were found to catalyze the coupling of silanes and amines under mild conditions. Utilizing 2.0 equiv. of R2NH per 1.0 equiv. of an Si-H bond in silane, nBuLi rapidly coupled primary and secondary amines with PhSiH3, PhMeSiH2, Ph2SiH2, PhMe2SiH, Ph2MeSiH, and Ph3SiH to high conversions in 0.5-1 h at ambient temperatures. Alkyl silanes such as Et3SiH and tBu2SiH2 were also accessible using nBuLi. Hammett competition experiments between tBuNH2 and (p-X-C6H4)Ph2SiH using nBuLi demonstrated rate-acceleration with electron-withdrawing substituents on silane. These results pointed to a mechanism involving nucleophilic attack of a metal-amido on silane. Notably, the identity of the organolithium reagent was general, which highlights the ubiquity of this methodology. Group I alkoxides subsequently emerged as versatile main group catalysts for heterodehydrocoupling. Several alkoxide and phenoxide compounds were tested under catalytic conditions, with KOtAmyl emerging as the most efficient precatalyst. Notably, PhNH2 was coupled to PhSiH3, PhMeSiH2, Ph2SiH2, and Ph3SiH using 2.5 mol % of KOtAmyl, affording aminosilane products in high conversions after 2 h at 40 °C. Efforts to uncover the mechanism and elucidate this unique activity are discussed.