Visible-Light-Induced Olefin Activation Using 3D Aromatic Boron-Rich Cluster Photooxidants

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• 作者：Marco S. Messina ; Jonathan C. Axtell ; Yiqun Wang ; Paul Chong ; Alex I. Wixtrom ; Kent O. Kirlikovali ; Brianna M. Upton ; Bryan M. Hunter ; Oliver S. Shafaat ; Saeed I. Khan ; Jay R. Winkler ; Harry B. Gray ; Anastassia N. Alexandrova ; Heather D. Maynard ; Alexander M. Spokoyny
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：June 8, 2016
• 年：2016
• 卷：138
• 期：22
• 页码：6952-6955
• 全文大小：392K
• 年卷期：0
• ISSN：1520-5126

文摘

We report a discovery that perfunctionalized icosahedral dodecaborate clusters of the type B₁₂(OCH₂Ar)₁₂ (Ar = Ph or C₆F₅) can undergo photo-excitation with visible light, leading to a new class of metal-free photooxidants. Excitation in these species occurs as a result of the charge transfer between low-lying orbitals located on the benzyl substituents and an unoccupied orbital delocalized throughout the boron cluster core. Here we show how these species, photo-excited with a benchtop blue LED source, can exhibit excited-state reduction potentials as high as 3 V and can participate in electron-transfer processes with a broad range of styrene monomers, initiating their polymerization. Initiation is observed in cases of both electron-rich and electron-deficient styrene monomers at cluster loadings as low as 0.005 mol%. Furthermore, photo-excitation of B₁₂(OCH₂C₆F₅)₁₂ in the presence of a less activated olefin such as isobutylene results in the production of highly branched poly(isobutylene). This work introduces a new class of air-stable, metal-free photo-redox reagents capable of mediating chemical transformations.