Download or read book Design, Synthesis, and Study of Silanediols as Homogeneous, Hydrogen-bonding Organocatalysts for Asymmetric Transformation written by Ngon Thi Tran and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Synthesis and the first proof-of-concept for silanediol hydrogen-bonding organocatalysis are demonstrated, showing that organic silanediols exhibit a new mode of activation for catalysis (Chapters 2 and 3). Novel silanediols catalyze the Diels-Alder and the Michael reactions with up to 81 and 91 % yields, respectively. Preliminary mechanistic studies show that there are multiple catalytically active silanediol species and that silanediol catalysis involves cooperative hydrogen-bonding effects and SiOH-acidification. These results suggest that steric and electronic effects are not the only factors affecting silanediol catalysis. Preliminary investigations also demonstrate that high solubility and bifunctionality generally improved the catalyst activity and versatility of silanediols. The synthetic efforts presented within provide strong evidence that kinetically stable and soluble silanediols, including bifunctional and fairly acidic silanediols, will be consistently obtained by incorporating substituents that sufficiently increase the immediate steric environment of a silicon center and that are lipophilic (Chapter 4). These strategies are important for reproducible silanediol catalytic results, because our novel silanediols are resistant to polymerization and highly tolerant of other functional groups. A synthetic strategy was successfully developed to incorporate fairly basic groups (e.g. tertiary amine) in silanediol catalyst design, which is described in Chapter 4. As presented in Chapters 5-7, the intrinsic acidity of silanediols is highly tunable and is comparable to that of known hydrogen-bonding organocatalysts. In collaboration with the Jeehiun Lee Group at Rutgers University, new experimental gas-phase acidity values for a series of novel silanols and a variety of dual hydrogen-bonding organocatalysts were measured. Optimization of computational methods demonstrates that B3LYP/6-311++G(2df,p)//B3LYP/6-311++G(2df,p) predicts gas-phase acidity of dual hydrogen-bonding organocatalysts, including silanediols, with high accuracy ([delta]H[subscript acid] [less than or equal to] 3 kcal mol−1). Our investigation shows that the wider range (-10.0 to 15.5) of accurate pKa prediction ([delta]pK[subscript a] [less than or equal to] 1) and greater functional group tolerance of the cluster continuum method also apply to silanols and siloxanols. With these computational methods, a systematic investigation of the effects of hyperconjugation, inductive effects, intramolecular hydrogen bonding, and cooperative hydrogen bonding on the acidity of molecular silanols and siloxanols was performed. Our acidity studies demonstrate that there is greater acidity enhancement in the carbon-to-silicon switch strategy of bioactive molecules than previously reported, which were based on extrapolation. Molecular recognition studies of silanediols in the solid and liquid states were performed as described in Chapters 8 and 9. Based on a series of 24 X-ray crystal structures, our co-crystallization studies revealed that it is actually rare for silanediols to interact with neutral Lewis bases through dual hydrogen-bond donation. Instead, silanediols prefer to self-aggregate as a closed cyclic dimer and interact with neutral functionalities through single-point hydrogen bonding. NMR studies in solution demonstrate that the intrinsic binding affinity of silanediols is significantly affected by solvent selection, intrinsic acidity of silanediols, Lewis basicity of hydrogen-bond acceptors, intramolecular hydrogen bonding, and complementary hydrogen bonding with co-solvates/guests. High concentration studies revealed that organosilanols participate in extensive self-recognition as well as cooperative H-bonding that generally lead to a substantial increase in molecular associations. These studies also demonstrate that the intrinsic properties (e.g. acidity and binding affinity) of organosilanols can be masked by solvents (e.g. DMSO) because silanols have strong hydrogen bonding capabilities and interact significantly with solvent molecules.