• Construction of C-C bonds via photoreductive coupling of ketones and aldehydes in the metal-organic-framework MFM-300(Cr)

      Luo, Tian; Li, Lili; Chen, Yinlin; orcid: 0000-0001-7878-2063; An, Jie; email: jie_an@cau.edu.cn; Liu, Chengcheng; Yan, Zheng; Carter, Joseph H.; orcid: 0000-0001-5530-7390; Han, Xue; Sheveleva, Alena M.; Tuna, Floriana; orcid: 0000-0002-5541-1750; et al. (Nature Publishing Group UK, 2021-06-11)
      Abstract: Construction of C-C bonds via reductive coupling of aldehydes and ketones is hindered by the highly negative reduction potential of these carbonyl substrates, particularly ketones, and this renders the formation of ketyl radicals extremely endergonic. Here, we report the efficient activation of carbonyl compounds by the formation of specific host-guest interactions in a hydroxyl-decorated porous photocatalyst. MFM-300(Cr) exhibits a band gap of 1.75 eV and shows excellent catalytic activity and stability towards the photoreductive coupling of 30 different aldehydes and ketones to the corresponding 1,2-diols at room temperature. Synchrotron X-ray diffraction and electron paramagnetic resonance spectroscopy confirm the generation of ketyl radicals via confinement within MFM-300(Cr). This protocol removes simultaneously the need for a precious metal-based photocatalyst or for amine-based sacrificial agents for the photochemical synthesis.
    • Refinement of pore size at sub-angstrom precision in robust metal–organic frameworks for separation of xylenes

      Li, Xiaolin; Wang, Juehua; Bai, Nannan; Zhang, Xinran; orcid: 0000-0002-0734-6173; Han, Xue; da Silva, Ivan; orcid: 0000-0002-4472-9675; Morris, Christopher G.; Xu, Shaojun; orcid: 0000-0002-8026-8714; Wilary, Damian M.; Sun, Yinyong; orcid: 0000-0002-5570-5089; et al. (Nature Publishing Group UK, 2020-08-27)
      Abstract: The demand for xylenes is projected to increase over the coming decades. The separation of xylene isomers, particularly p- and m-xylenes, is vital for the production of numerous polymers and materials. However, current state-of-the-art separation is based upon fractional crystallisation at 220 K which is highly energy intensive. Here, we report the discrimination of xylene isomers via refinement of the pore size in a series of porous metal–organic frameworks, MFM-300, at sub-angstrom precision leading to the optimal kinetic separation of all three xylene isomers at room temperature. The exceptional performance of MFM-300 for xylene separation is confirmed by dynamic ternary breakthrough experiments. In-depth structural and vibrational investigations using synchrotron X-ray diffraction and terahertz spectroscopy define the underlying host–guest interactions that give rise to the observed selectivity (p-xylene < o-xylene < m-xylene) and separation factors of 4.6–18 for p- and m-xylenes.
    • The Origin of Catalytic Benzylic C−H Oxidation over a Redox‐Active Metal–Organic Framework

      Kimberley, Louis; Sheveleva, Alena M.; orcid: 0000-0001-6190-5944; Li, Jiangnan; Carter, Joseph H.; Kang, Xinchen; Smith, Gemma L.; Han, Xue; Day, Sarah J.; Tang, Chiu C.; Tuna, Floriana; email: Floriana.Tuna@manchester.ac.uk; et al. (2021-06-04)
      Abstract: Selective oxidation of benzylic C−H compounds to ketones is important for the production of a wide range of fine chemicals, and is often achieved using toxic or precious metal catalysts. Herein, we report the efficient oxidation of benzylic C−H groups in a broad range of substrates under mild conditions over a robust metal–organic framework material, MFM‐170, incorporating redox‐active [Cu2II(O2CR)4] paddlewheel nodes. A comprehensive investigation employing electron paramagnetic resonance (EPR) spectroscopy and synchrotron X‐ray diffraction has identified the critical role of the paddlewheel moiety in activating the oxidant tBuOOH (tert‐butyl hydroperoxide) via partial reduction to [CuIICuI(O2CR)4] species.
    • The Origin of Catalytic Benzylic C−H Oxidation over a Redox‐Active Metal–Organic Framework

      Kimberley, Louis; Sheveleva, Alena M.; orcid: 0000-0001-6190-5944; Li, Jiangnan; Carter, Joseph H.; Kang, Xinchen; Smith, Gemma L.; Han, Xue; Day, Sarah J.; Tang, Chiu C.; Tuna, Floriana; email: Floriana.Tuna@manchester.ac.uk; et al. (2021-06-04)
      Abstract: Selective oxidation of benzylic C−H compounds to ketones is important for the production of a wide range of fine chemicals, and is often achieved using toxic or precious metal catalysts. Herein, we report the efficient oxidation of benzylic C−H groups in a broad range of substrates under mild conditions over a robust metal–organic framework material, MFM‐170, incorporating redox‐active [Cu2II(O2CR)4] paddlewheel nodes. A comprehensive investigation employing electron paramagnetic resonance (EPR) spectroscopy and synchrotron X‐ray diffraction has identified the critical role of the paddlewheel moiety in activating the oxidant tBuOOH (tert‐butyl hydroperoxide) via partial reduction to [CuIICuI(O2CR)4] species.