Loh Ying Kai, Porteous Kieran, Fuentes M Ángeles, Do Dinh Cao Huan, Hicks Jamie, Aldridge Simon
Inorganic Chemistry Laboratory, Department of Chemistry , University of Oxford , South Parks Road , Oxford OX1 3QR , U.K.
J Am Chem Soc. 2019 May 22;141(20):8073-8077. doi: 10.1021/jacs.9b03600. Epub 2019 May 9.
We disclose the synthesis and structural characterization of the first acid-free anionic oxoborane, [K(2.2.2-crypt)][(HCDippN)BO] (1) (Dipp = 2,6- PrCH), which is isoelectronic with classical carbonyl compounds. 1 can readily be accessed from its borinic acid by a simple deprotonation/sequestration sequence. Crystallographic and density functional theory (DFT) analyses support the presence of a polarized terminal B═O double bond. Subsequent π bond metathesis converts the B═O bond to a heavier B═S containing system, affording the first anionic thioxoborane [K(2.2.2-crypt)][(HCDippN)BS] (2), isoelectronic with thiocarbonyls. Facile B═O bond cleavage can also be achieved to access B-H and B-Cl bonds and, via a remarkable oxide (O) ion abstraction, to generate a borenium cation [(HCDippN)B(NCH)][OTf] (4). By extension, 1 can act as an oxide transfer agent to organic substrates, a synthetic role traditionally associated with transition-metal compounds. Hence we show that B-O linkages, which are often considered to be thermodynamic sinks, can be activated under mild conditions toward bond cleavage and transfer, by exploiting the higher reactivity inherent in the B═O double bond.
我们报道了首例无酸阴离子氧硼烷[K(2.2.2-穴醚)][(HCDippN)BO] (1)（Dipp = 2,6-二异丙基苯基）的合成及结构表征，它与经典羰基化合物等电子。通过简单的去质子化/螯合序列，可从其硼酸轻松制得1。晶体学和密度泛函理论（DFT）分析支持存在极化的末端B═O双键。随后的π键复分解将B═O键转化为含较重B═S的体系，得到首例阴离子硫氧硼烷[K(2.2.2-穴醚)][(HCDippN)BS] (2)，它与硫羰基等电子。还可轻松实现B═O键的断裂以得到B-H键和B-Cl键，并通过显著的氧（O）离子夺取反应生成硼正离子[(HCDippN)B(NCH)][OTf] (4)。进而，1可作为氧化物转移剂作用于有机底物，这是传统上与过渡金属化合物相关的合成作用。因此我们表明，通常被认为是热力学稳定产物的B-O键，可通过利用B═O双键固有的更高反应活性，在温和条件下被激活以实现键的断裂和转移。
