Metal–Organic Complex-Functionalized Phosphovanadomolybdates Enable Synergistic O ₂ Activation in Biomimetic Multistep Oxidative Self-Coupling: o -Aminophenols to Aminophenoxazinones

Achieving the additive-free oxidative self-coupling of o -aminophenols (OAPs) to form pharmacologically active aminophenoxazinones (APXOs) via a heterogeneous process under an oxygen (O 2 ) atmosphere is of great significance for sustainable development. Herein, two isostructural polyoxometalate-based coordination polymers with the general formula [M( i -Pr-Im) 4 ][M( i -Pr-Im)(Phen) 2 ] 2 [HPMo 8 V 6 O 42 ]· n H 2 O (M = Co ( 1 ) or Ni ( 2 ); i -Pr-Im = N -isopropylimidazole, Phen = 1,10-phenanthroline) have been synthesized and thoroughly characterized. Needing no additives, both compounds are capable of effectively catalyzing the oxidation of OAP to APXO using O 2 as an oxidant, with yields of 96.0% for 1 and 82.0% for 2 . Experimental findings demonstrate that the higher catalytic performance of 1 is attributed to the synergistic work between the Co sites and the {PMo 8 V 6 } units in its structure, with the catalytic process involving superoxide radicals. Catalyst 1 can be easily recovered by centrifugation and reused at least five times without compromising performance, and the successful scale-up to a gram-scale reaction (100 mmol, 10.9 g) resulted in a 93.0% yield of APXO (46.5 mmol, 9.86 g) and a turnover number of 6200. This work represents the first application of polyoxometalate-based heterogeneous catalysis for additive-free, O 2 -driven APXO synthesis and provides a promising platform for sustainable oxidative coupling.