Catalyst-free 2+2 Photodimerization of 1,4-Bis[2-(4-pyridyl)ethenyl]-benzene in Solution Under Low Power UV Irradiation
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doi: 10.1007/s40242-020-9116-3
Article
Catalyst-free 2+2 Photodimerization of 1,4-Bis[2-(4-pyridyl)ethenyl]-benzene in Solution Under Low Power UV Irradiation CHU Ning, XU Shuping and XU Weiqing* State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun 130012, P. R. China Abstract Two different kinds of configurations of 1,4-bis[2-(4-pyridyl)ethenyl]-benzene(trans-bpeb and cis-bpeb) were achieved, and a bpeb dimer was synthesized in dimethyl sulfoxide(DMSO). Compared with the previous work that synthesized the bpeb dimer or polymer in crystal with a template agent needed, the reaction occur red in a solution phase in the present method. A hand-held ultraviolet lamp(365 nm) with the power of 12 W and the Watt density of 0.35 mW/cm2 can realize the photodimerization of bpeb, instead of the high-power mercury lamp in most previous studies. Unlike other 2+2 cycloaddition in liquid state using catalysts even noble metals, no catalysts were required here, which is cost-saving. Only the trans-pbeb can start the cycloaddition and the formation of the close J-aggregations of trans-pbeb in DMSO is a precondition for explaining the 2+2 photodimerization. The productivity for the 2+2 cycloaddition product was achieved as 55.6%. Keywords 2+2 Photodimerization; 1,4-Bis[2-(4-pyridyl)ethenyl]-benzene; Catalyst-free
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Introduction
Photochemical reactions have been widely utilized to synthesize cycloalkanes and can adjust the function of materials in a spatial and temporal manner. Only some molecules with special structures could meet the need of 2+2 photodimerization. 1,4-Bis[2-(4-pyridyl)ethenyl]-benzene(bpeb) and its derivatives, which contain special functional groups like double bond and pyridine, have been widely applied in the fields of ion detection[1], coordination compound[2,3], metal-organic frameworks(MOF)[4], co-crystal materials[5,6], laser Raman molecular probe[7,8], and molecular self-assembly[9,10], etc. There are two carbon-carbon double bonds(C=C) in one bpeb molecule, which may generate 2+2 cycloaddition reactions between two
bpeb molecules on four C=C bonds(dimer H2 in Scheme 1) or each C=C of two bpebs(dimer H1 or dimer J). There are several methods to obtain the dimer in crystal or solid while only very few methods to obtain that in liquid. MacGillivray et al.[11―13] achieved a bpeb dimer via the 2+2 cycloaddition in an H-aggregation crystal with the resorcinol and its derivative as template agents. In this bpeb crystal, two bpeb molecules were stacked through the formation of two hairpin structures by hydrogen-bond interaction of the hydroxide groups of resorcinol on pyridine rings, which causes two C=C bonds parallelly arranged with a distance within 0.42 nm, allowing the 2+2 cycloaddition to proceed on four C=C bonds of two bpeb (dimer H2). Moreover, another bpeb dimer in an H-aggregation co-crystal can start the cycloaddition on one of the two double
Scheme 1 Reactants and predicted products ——————————— *Corresponding author. Email: [email protected] Received Decembe
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