Self-Adaptive Dirhodium Complexes in a Metal–Organic Framework for Synthesis of N–H Aziridines

Conformational dynamics of active
sites in enzymes enable great
control over the catalytic process. Herein, we constructed a metal–organic
framework with conformationally dynamic active sites (Rh2-ZIF-8). The active sites in Rh2-ZIF-8 were composed of
the imidazolate-bridged bimetallic center with a catalytic dirhodium
moiety and structural zinc site. Even though the coordination sphere
of the dirhodium species was saturated with two circularly arranged
esp groups and two axial 2-MeIm ligands, it could still effectively
catalyze the direct synthesis of N–H aziridines from olefins
with high activity. We found that such a self-adaptive catalytic process
was based on the dynamic breakage and reformation of the rhodium–zinc
imidazolate bridges. Interestingly, the in situ generated
dirhodium site with a unique Rh2(esp)2(2-MeIm)1 configuration was able to exhibit obviously enhanced selectivity
compared to homogeneous catalyst Rh2(esp)2.
Furthermore, the surrounding zinc imidazolate groups could effectively
protect the dirhodium moieties from harsh environments, and this ultimately
endowed it with high stability.