Pyrene-based metal–organic framework NU-1000 photocatalysed atom-transfer radical addition for iodoperfluoroalkylation and (Z)-selective perfluoroalkylation of olefins by visible-light irradiation

摘要

The photocatalytic atom-transfer radical addition (ATRA) of perfluoroalkyl iodides onto olefins is of potential biointerest; the relatively negative reductive potential of perfluoroalkyl iodide makes it difficult to generate the perfluoroalkyl radical by the photoinduced single-electron transfer from the excited state of the photocatalyst. In the presence of the easily available well-known pyrene-based metal–organic framework (MOF) NU-1000, the ATRA was achieved for iodoperfluooralkylation of olefins in a heterogeneous mode upon 405 nm visible-light irradiation with LEDs. The investigation supports a mechanism whereby the pyrene-based chromophores within NU-1000 photochemically generate the reactive radical species by sensitisation of the perfluoroalkyl iodides through an energy-transfer (EnT) pathway. Besides the activation of singlet oxygen for oxidative application, it is the first time to directly utilise the photoinduced EnT process of MOFs in organic transformations. Compared with the photocatalysis using homogeneous free ligand or other pyrene-based MOFs, the spatial isolation of chromophores in NU-1000 is believed to hamper the destructive excited-state energy loss from self-quenching or interligand interactions, ensuring the efficiency of reaction. When employing conjugated arylalkenes as substrates, the photocatalytic ATRA reaction, the HI elimination of the ATRA product, and the EnT-mediated ( E )/( Z )-isomerisation could be merged together in one-pot to afford highly ( Z )-selective perfluoroalkyl styrenes, which might be attractive in the pharmaceutical field.