Pietsch Sabrina, Neeve Emily C, Apperley David C, Bertermann Rüdiger, Mo Fanyang, Qiu Di, Cheung Man Sing, Dang Li, Wang Jianbo, Radius Udo, Lin Zhenyang, Kleeberg Christian, Marder Todd B
Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg (Germany).
Chemistry. 2015 May 4;21(19):7082-98. doi: 10.1002/chem.201500235. Epub 2015 Apr 15.
Lewis base adducts of tetra-alkoxy diboron compounds, in particular bis(pinacolato)diboron (B2 pin2 ), have been proposed as the active source of nucleophilic boryl species in metal-free borylation reactions. We report the isolation and detailed structural characterization (by solid-state and solution NMR spectroscopy and X-ray crystallography) of a series of anionic adducts of B2 pin2 with hard Lewis bases, such as alkoxides and fluoride. The study was extended to alternative Lewis bases, such as acetate, and other diboron reagents. The B(sp(2) )-B(sp(3) ) adducts exhibit two distinct boron environments in the solid-state and solution NMR spectra, except for (4-tBuC6 H4 O)B2 pin2 , which shows rapid site exchange in solution. DFT calculations were performed to analyze the stability of the adducts with respect to dissociation. Stoichiometric reaction of the isolated adducts with two representative series of organic electrophiles-namely, aryl halides and diazonium salts-demonstrate the relative reactivities of the anionic diboron compounds as nucleophilic boryl anion sources.
四烷氧基二硼化合物的路易斯碱加合物，特别是双（频哪醇合）二硼（B2pin2），已被认为是无金属硼化反应中亲核硼基物种的活性来源。我们报告了一系列B2pin2与硬路易斯碱（如醇盐和氟化物）的阴离子加合物的分离及其详细的结构表征（通过固态和溶液核磁共振光谱以及X射线晶体学）。该研究扩展到了其他路易斯碱，如乙酸盐，以及其他二硼试剂。除了(4-tBuC6H4O)B2pin2在溶液中显示出快速的位点交换外，B(sp(2))-B(sp(3))加合物在固态和溶液核磁共振光谱中表现出两种不同的硼环境。进行了密度泛函理论计算以分析加合物相对于解离的稳定性。分离出的加合物与两个代表性系列的有机亲电试剂——即芳基卤化物和重氮盐——的化学计量反应证明了阴离子二硼化合物作为亲核硼基阴离子源的相对反应活性。
