Hydrogen-Bond-Enhanced Photoreforming of Biomass Furans over a Urea-Incorporated Cu(II) Porphyrin Framework.

ABSTRACT

Solar-driven upgrading of biomass-derived 5-hydroxylmethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) holds great promise for sustainable production of bio-plastics and resins. However, the process is limited by poor selectivity and sluggish kinetics due to the vertical coordination of HMF at relatively strong metal sites. Here, we purposely developed a Cu(II) porphyrin framework featuring side-chain incorporated urea linkages, denoted as TBUPP-Cu MOF, to render HMF a weak hydrogen bond at the urea site and flat adsorption via π-π stacking with the benzene moiety. The unique configuration promotes the approaching of -CHO of HMF to the photoexcited porphyrin ring towards kinetically and thermodynamically favourable intermediate formation and subsequent desorption. The charge localisation and orbital energy alignment enable the selective activation of O2 over the porphyrin to generate ⋅O2 - and 1O2 instead of highly oxidative H2O2 and ⋅OH via spin-flip electron transfer, which drive the ambient oxidation of proximal -CHO. The effective utilisation of redox species and circumvented over-oxidation facilitate a FDCA selectivity of >90 % with a high turnover number of 193 molHMF molCu -1. The facile purification of high-purity FDCA and zero-waste recycling of intermediates and durable catalyst feature TBUPP-Cu MOF a promising photo-oxidation platform towards net-zero biorefining and organic transformations.