Supramolecular catalysis is established to modify reaction
kinetics
by substrate encapsulation, but manipulating the thermodynamics of
electron-transfer reactions remains unexplored. Herein, we reported
a new microenvironment-shielding approach to induce an anodic shift
in the redox potentials of hydrazine substrates, reminiscent of the
enzymatic activation for N–N bond cleavage within a metal–organic
capsule H1. Equipped with the catalytic active cobalt
sites and substrate-binding amide groups, H1 encapsulated
the hydrazines to form the substrate-involving clathration intermediate,
triggering the catalytic reduction N–N bond cleavage when electrons
were acquired from the electron donors. Compared with the reduction
of free hydrazines, the conceptual molecular confined microenvironment
decreases the Gibbs free energy (up to −70 kJ mol–1), which is relevant to the initial electron-transfer reaction. Kinetic
experiments demonstrate a Michaelis–Menten mechanism, which
involves the formation of the pre-equilibrium of substrate-binding,
followed by bond cleavage. Then, the distal N is released as NH3 and the product is squeezed. Integrating fluorescein into H1 enabled the photoreduction of N2H4 with an initial rate of ca. 1530 nmol min–1 into
ammonia, comparable to that of natural MoFe proteins; thus, the approach
provides an attractive manifold toward mimicking enzymatic activation.