Enantioselective hydrosilylation of unsaturated carbon-heteroatom bonds (C&z.dbd;N, C&z.dbd;O) catalyzed by [Ru-S] complexes: a theoretical study

• Published in: RSC advances Vol. 1; no. 16; pp. 9431 - 9437
• Main Authors: Zhou, Miao-Miao, Chen, Guanghui, Dang, Li
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 04.03.2020; The Royal Society of Chemistry
• Subjects: Carbon; Cartesian coordinates; catalysts; Cations; Chemistry; chemoselectivity; cleavage (chemistry); Dehydrogenation; Density functional theory; enamines; Enantiomers; enantioselectivity; enol ethers; hydrogen; Hydrogen bonds; Hydrosilylation; Imines; Ketones; Lewis acids; Ligands; phosphine; Phosphines; Reaction mechanisms; Ruthenium; Ruthenium compounds; silane; Silicon; silylation
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/c9ra10760f

A detailed theoretical study on the mechanism of enanthioselective hydrosilylation of imines and ketones catalyzed by the ruthenium( ii ) thiolate catalyst [Ru-S] ([ L* -Ru(SDmp)] + [BAr 4 F ] − ) with a chiral monodentate phosphine ligand is carried out in this work. We elucidate all the pathways leading to the main products or by products mediated by the [Ru-S] complex in order to have deep understanding of the chemoselectivity and enantioselectivity. The DFT (Density Functional Theory) calculations show that the reaction mechanism including: (1) Si-H bond cleavage by the dual activity of Ru-S bond; (2) the generation of a sulfur-stabilized silane cation; (3) the electrophilic attack of silane cation to N&z.dbd;C/O&z.dbd;C; (4) hydrogen transfer from Ru to carbon cation. The hydrosilylation products are found to be the final products rather than the dehydrogenative ones, which is consistent with the experimental results. The dehydrogenative silylation reaction pathways which give N- or O-silylated enamine/enol ether are reversible according to our calculations. The computational results also show that the electrophilic attack of silicon to N&z.dbd;C/O&z.dbd;C is the rate-determining step and the ee value can be improved significantly with more bulky model phosphine ligand based on the same calculation methods. A detailed theoretical study on the mechanism of enanthioselective hydrosilylation of imines and ketones catalyzed by the ruthenium( ii ) thiolate catalyst with a chiral monodentate phosphine ligand is carried out in this work.