Navigating the Bio-Inspired Structure-Function Landscape: Spectroscopy Driven Finding of Hidden Radical Oxidation in...

The conventional synthesis of acetophenone via the Friedel-Crafts reaction is a highly waste-intensive process. Consequently, the development of more sustainable and efficient alternatives is important. In this regard, radical oxidation represents a promising, environmentally benign route for acetophenone production. In this work, we designed a cobalt porphyrin-based metalated porous organic polymer (Co@POR-POP), a highly active catalytic system, offering a potentially viable and cleaner approach to acetophenone production, utilizing styrene as the starting material. The catalyst exhibits a high surface area (BET = 650 m²g^-1) with bimodal pores, and delivers more than 90% yield of acetophenone under ambient conditions with excellent selectivity. Synchrotron-based XAFS spectroscopy study revealed a square-planar Co-N₄ coordination environment with coordination number (CN) ≈4 and Co─N bond distance of ∼1.93 Å, with no evidence of Co-Co scattering, confirming the presence of isolated active sites. In situ EPR spectroscopy investigation displayed g_⊥ = 2.049 and g_∥ = 1.985 with hyperfine couplings A_⊥ = 49.8 MHz and A_∥ = 46.16 MHz, alongside an organic radical signal at g = 2.003. Spin-trapping with DMPO detected both hydrogen (•H) and styrene (•C) radicals, validating a radical-mediated mechanism. DFT calculations established a thermodynamically favourable pathway with an overall energy drop of -4.5 eV, supported by spin density localization at the Co centre and significant d-π orbital overlap facilitating O₂ activation. Overall, this work presents a new avenue of exploring novel organic transformation reactions using metalated porous organic polymer, opening scope for further investigations in this domain.