摘要/Abstract
硅卡宾（R2Si：，silylene）是卡宾的相似体，可以作为配体与金属形成配合物.由于硅的原子半径比碳大，硅卡宾可与Lewis碱配位形成三配位甚至四配位的化合物同时保持很强的配位能力.因此，硅卡宾兼具卡宾和膦配体的结构特征，在稳定新颖的金属配合物及均相催化领域或具有更大的调控空间.本工作报道硅卡宾铁氮气配合物[PhC （t-BuN）2SiCH2C （t-Bu） NAr]FeN2（D，Ar＝2，6-（i-Pr）2C6H3）催化的炔烃的选择性硼氢化反应.研究发现，该配合物对炔烃的硼氢化反应具有很好的区域及立体选择性，主要生成E式构型产物并表现出很好的官能团耐受性.该研究表明，硅卡宾对过渡金属催化具有很好的调控作用，具有很好的研究潜力.
关键词: 硅卡宾, 铁催化, 硼氢化, 炔烃, 氮气
Silylenes, isoelectronic with carbenes, are a kind of key intermediates in organosilicon chemistry. They possess a lone pair and an empty orbital on the silicon center, and thus could be used as donors and acceptors. Consequently, they could form complexes with various metals to support new structures and chemistry similar to both carbenes and phosphines. Iron complexes played important roles in the development of catalysts because of the inexpensive, nontoxic and sustainable characteristics.Catalytic hydroboration of alkynes presents the most atom-economic and straightforward protocol for the synthesis of vinylboranes which are indispensable intermediates for C—C coupling reactions. For the catalytic hydroboration of alkynes with iron catalysts, Enthaler’s group developed the first iron catalytic system for hydroboration of alkynes by using Fe2(CO)9 (A, Chart 1) as the catalyst. Almost at the same time, Thomas’s group reported the bis(imino)pyridine derived iron complexes (B) in combination with an activator for catalytic hydroboration of alkynes and alkenes. In 2017, Nishibayashi and co-workers employed an iron(II) hydride complex (C) supported by a PNP pincer ligand for catalytic E-selective hydroboration of alkynes. In 2020, Findlater et al. reported the regioselective hydroboration of alkynes and alkenes with iron complexes supported by bis(2,6-diisopropylaniline)acenaphthene ligands. However, these catalysts still suffered from limited substrate scope or harsh conditions. The development of highly selective catalysts for a wide substrate scope is still desirable. On the basis of our design on silylene ligands for iron chemistry, we are interested in the silylene-iron complexes for catalytic hydroboration reactions. In this paper, hydroborylation of terminal alkynes catalyzed by a neutral silylene-imine iron(0) dinitrogen complex D was studied. The reaction is highly regio- and stereoselective and almost exclusively gave E-hydroboration products. The optimized reaction conditions are as following: To a dried Schlenk tube were added complex D (0.006 g, 0.01 mmol), toluene (1.0 mL), alkyne (0.20 mmol), and catechol borane (0.02 g, 0.20 mmol). After the mixture was stirred at 80 ℃ for 24 h, it was cooled down to room temperature. The solvents were removed under vacuum and the residue was purified by flash chromatography on silica gel to afford the desired products.
Key words: silylene, iron-catalyzed, hydroboration, alkyne, dinitrogen
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