Site‐Isolated Rhodium(II) Metalloradicals Catalyze Olefin Hydrofunctionalization

• Published in: Angewandte Chemie International Edition 2024-04, Vol.63 (18), p.e202401375-n/a
• Main Authors: Qiu, Zihang, Deng, Hao, Neumann, Constanze N.
• Format: Article
• Language: English
• Subjects: Catalysis; Dimerization; hydrogermylation catalysis; hydrosilylation catalysis; Intermediates; Metal-organic frameworks; MOF catalysis; MOF site-isolation; Nanoparticles; Photolysis; Porphyrins; Rh(II) metalloradicals; Rhodium
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202401375

Rh(II) porphyrin complexes display pronounced metal‐centered radical character and the ability to activate small molecules under mild conditions, but catalysis with Rh(II) porphyrins is extremely rare. In addition to facile dimerization, Rh(II) porphyrins readily engage in kinetically and thermodynamically facile reactions involving two Rh(II) centers to generate stable Rh(III)−X intermediates that obstruct turnover in thermal catalysis. Here we report site isolation of Rh(II) metalloradicals in a MOF host, which not only protects Rh(II) metalloradicals against dimerization, but also allows them to participate in thermal catalysis. Access to PCN‐224 or PCN‐222 in which the porphyrin linkers are fully metalated by Rh(II) in the absence of any accompanying Rh(0) nanoparticles was achieved via the first direct MOF synthesis with a linker containing a transition‐metal alkyl moiety, followed by Rh(III)−C bond photolysis. Heterogenization of Rh(II) porphyrin catalysts in a metal–organic framework is crucial for catalyst turnover in thermal olefin hydrosilylation and hydrogermylation. Unlike MOF‐supported metalloradical catalysts, homogeneous analogues convert to closed shell species that obstruct catalytic turnover. Site‐isolated Rh(II) metalloradicals are readily accessed via MOF synthesis with a linker containing a metal‐alkyl bond followed by Rh−C photolysis.