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Polyradical cages are of great interest because they show very fascinating physical and chemical properties, but many challenges remain, especially for their synthesis and characterization. Herein, we present the synthesis of a polyradical cation cage 14.+ through post‐synthetic oxidation of a redox‐active phenothiazine‐based Pd2L4‐type coordination cage 1. It′s worth noting that 1 exhibits excellent reversible electrochemical and chemical redox activity due to the introduction of a bulky 3,5‐di‐tert‐butyl‐4‐methoxyphenyl substituent. The generation of 14.+ through reversible electrochemical oxidation is investigated by in situ UV/Vis‐NIR and EPR spectroelectrochemistry. Meanwhile, chemical oxidation of 1 can also produce 14.+ which can be reversibly reduced back to the original cage 1, and the process is monitored by EPR and NMR spectroscopies. Eventually, we succeed in the isolation and single crystal X‐ray diffraction analysis of 14.+, whose electronic structure and conformation are distinct to original 1. The magnetic susceptibility measurements indicate the predominantly antiferromagnetic interactions between the four phenothiazine radical cations in 14.+. We believe that our study including the facile synthesis methodology and in situ spectroelectrochemistry will shed some light on the synthesis and characterization of novel polyradical systems, opening more perspectives for developing functional supramolecular cages. [ABSTRACT FROM AUTHOR]

Metal‐organic frameworks (MOFs) consisting of organic radicals are of great interest because they have exhibited unique and intriguing optical, electronic, magnetic, and chemo‐catalytic properties, and thus have demonstrated great potential applications in optical, electronic, and magnetic devices, and as catalysts. However, the preparation of MOFs bearing stable organic radicals is very challenging because most organic radicals are highly reactive and difficult to incorporate into the framework of MOFs. Herein we reported a post‐synthetic modification strategy to prepare a novel MOF containing phenazine radical cations, which was used as heterogeneous catalyst for aza‐Diels‐Alder reaction. The zinc‐based metal‐organic framework Zn2(PHZ)2(dabco) (N) was successfully synthesized from 5,10‐di(4‐benzoic acid)‐5,10‐dihydrophenazine (PHZ), triethylene diamine (dabco) with Zn(NO3)2 ⋅ 6H2O by solvothermal method. The as‐synthesized MOF N was partially oxidized by AgSbF6 to form MOF R containing ∼10% phenazine radical cation species. The resultant MOF R was found to keep the original crystal type of N and very persistent under ambient conditions. Consequently, MOF R was successfully employed in radical cation‐catalyzed aza‐Diels‐Alder reactions with various imine substrates at room temperature with high reaction conversion. Moreover, heterogeneous catalyst MOF R was reusable up to five times without much loss of catalytic activity, demonstrating its excellent stability and recyclability. Therefore, the post‐synthetic modification developed in this work is expected to become a versatile strategy to prepare radical‐based MOFs for the application of heterogeneous catalysts in organic synthesis. [ABSTRACT FROM AUTHOR]

Polyradical cages are of great interest because they show very fascinating physical and chemical properties, but many challenges remain, especially for their synthesis and characterization. Herein, we present the synthesis of a polyradical cation cage 1 4 ⋅ + through post-synthetic oxidation of a redox-active phenothiazine-based Pd 2 L 4 -type coordination cage 1. It's worth noting that 1 exhibits excellent reversible electrochemical and chemical redox activity due to the introduction of a bulky 3,5-di-tert-butyl-4-methoxyphenyl substituent. The generation of 1 4 ⋅ + through reversible electrochemical oxidation is investigated by in situ UV/Vis-NIR and EPR spectroelectrochemistry. Meanwhile, chemical oxidation of 1 can also produce 1 4 ⋅ + which can be reversibly reduced back to the original cage 1, and the process is monitored by EPR and NMR spectroscopies. Eventually, we succeed in the isolation and single crystal X-ray diffraction analysis of 1 4 ⋅ + , whose electronic structure and conformation are distinct to original 1. The magnetic susceptibility measurements indicate the predominantly antiferromagnetic interactions between the four phenothiazine radical cations in 1 4 ⋅ + . We believe that our study including the facile synthesis methodology and in situ spectroelectrochemistry will shed some light on the synthesis and characterization of novel polyradical systems, opening more perspectives for developing functional supramolecular cages., (© 2024 Wiley-VCH GmbH.)