Systematic calculations on reactions of various allyl-metals towards carbonyl compounds and water were performed to understand why some discrete allyl-metals, even hydrolytically active ones, can proceed allylation in water (Chapter 1). Allylation is found to be thermodynamically favorable than hydrolysis. Calculated kinetic preferences towards allylation over hydrolysis are correlated with hydrolysis barriers. The later hydrolysis transition structures are, the higher hydrolysis barriers and the higher kinetic preferences for the allyl-metals to undergo allylation are....[ Read more ]

Systematic calculations on reactions of various allyl-metals towards carbonyl compounds and water were performed to understand why some discrete allyl-metals, even hydrolytically active ones, can proceed allylation in water (Chapter 1). Allylation is found to be thermodynamically favorable than hydrolysis. Calculated kinetic preferences towards allylation over hydrolysis are correlated with hydrolysis barriers. The later hydrolysis transition structures are, the higher hydrolysis barriers and the higher kinetic preferences for the allyl-metals to undergo allylation are.

Reaction mechanism, drawbacks and roles of the chelation on intermolecular hydroacylation were studied in Chapter 2.

Reaction mechanism of unusual hydrosilylation of carbonyl compounds catalyzed by a high-valent rhenium(V)-dioxo complex involving [2+2] addition, phosphine-assisted reduction and retro-[2+2] addition was supported by the calculations. Effects of ligands, metals and substrates on the addition across metal-ligand multiple bonds were also systematically studied. Moreover, another mechanism involving σ-bond metathesis and reduction was proposed for one neutral rhenium(V)-monooxo complex (Chapters 3-4).

Effects of bulkiness of ligands on the structure and thermo-stability of cationic ruthenium silylene complexes and reaction mechanisms for alkene hydrosilylation were studied (Chapter 5). Unique non-classical base-free ruthenium silylene structures were obtained. The bulky and realistic ruthenium complexes have lesser thermo-stabilities. The proposed [2_σ+2_π] addition pathway is sterically and electronically more superior to the Chalk-Harrod pathway. PⁱPr₃-assisted direct silane dissociation from the bulky [2_σ+2_π] addition products followed by coordination of silane reactants to regenerate active and bulky ruthenium silylene species is suggested to occur.

A novel mechanism involving oxidatively-added hydrometalation followed by direct and stereoselective formation of metallacyclopropene-like intermediates and eventually metallacyclopropene-form reductive silyl migration was derived from DFT methods (Chapter 6). Only this proposed mechanism can account for the unusual regio- and stereo-chemistry of alkynes hydrosilylation catalyzed by the cationic ruthenium complexes. Regioselectivity of hydrometalation was suggested to be finely tuned by the metals, ancillary ligands, silanes and alkynes.