报告主题：Development of Selective, Catalytic Reductive Transformations Based on Synthetic and Mechanistic Organometallic Chemistry

报 告 人：Sehoon Park 博士

报告时间：6月21日（周三）9:00

报告地点：理学院报告厅

报告主要内容：

Catalytic reduction of (unsaturated)functional groups is one of the most essential transformations in chemistry. For example, the early transition metal-initiated polymerization of a-olefins giving rise to the corresponding polyolefins is regarded as one of important reductive transformations, while the catalytic deoxygenative reduction of sugars to thermodynamically stable hydrocarbon fuels is also an attractive process in both academia and industry. On the other hand, the addition process of a Si-H bond of hydrosilanes across unsaturated functionalities, referred to as hydrosilylation is one of the most extensively studied and widely utilized synthetic methods. The feature of this method distinct from hydrogenation includes milder reaction conditions without special equipment, and easy tenability of the catalyst reactivity by simply choosing suitable silanes. Although transition metal-catalyzed hydrosilylation has been taking superior position in this context thus far, the use of precious metals of Pt, Rh, and Pd, and decomposition of the catalyst can be substantial obstacles in establishing the efficient hydrosilylation process. From a practical point of view, one might interest in developing either highly active transition metal hydrosilylation catalysts (e.g. Wilkinson’s catalyst, Karstedt’s catalyst) or environmentally-benign metal-free catalytic procedures (e.g. B(C₆F₅)₃/silane).

 In this talk, as the first part, we describe the cationic (a-diimine)Pd complex-promoted cyclopolymerization of a variety of functionalized 1,6-dienes to produce polymers containing five-membered repeating units with excellent chemo-, regio-, and stereoselectivities. With this strategy, we are able to synthesize unprecedented, various cyclic polymers possessing polar functional groups. An in-depth mechanistic investigation reveals that the active Pd center undergoes a rapid, reversible chain-walking process (b-H elim./re-addition) during the chain propagation. In the second part, we present the highly active Ir-catalyzed hydrosilylative reduction of carbonyls, epoxides, and carbon dioxide. Notably, the employed cationic Ir pincer complex as a single catalyst is found to promote a reduction of CO₂ to CH₄ with trialkylsilanes under 1 atm of CO₂ at 23 ^oC, achieving up to 8,300 turnovers. In the third part, we mainly discuss about the B(C₆F₅)₃-catalyzed silylative reductions of N-heteroarenes including quinolines and pyridines, giving hydroquinoline and hydropyridine products bearing new sp³ C-Si bonds in the b-position relative to the nitrogen atom. Mechanistic studies clearly show that the reaction proceeds via 1,4-hydrosilylation, followed by b-selective hydrosilylation at the enamine moiety. Being related with this silylative dearomatization, we also report the Ir-catalyzed 1,2-selective hydrosilylation of a variety of N-heteroaromatic compounds, in which mechanistic aspects are discussed more in detail. As the last part, we disclose the boron-based new catalytic systems for hydrosilylative transformations: (1) heterogeneous boron hydrosilylation catalyst with excellent selectivity and good recyclability; (2) (C₆F₅)₂BH-catalyzed hydrosilylative C-O bond cleavage of sugars with excellent chemo- and regioselectivities.

报告人简介：

欢迎全校师生参加！

注：本次讲座将纳入化学系继续教育课程。

理学院

2017年6月15日