Mechanistic Diversity in the Hydrolysis of Sarin by Single Transition-Metal Atoms on MOF-808

Zr-based metal–organic
frameworks (Zr-MOFs) are one of the
most promising materials for the decomposition of chemical warfare
nerve agents. We present a study of the hydrolysis reaction mechanism
of nerve agent sarin catalyzed by Zn(II) and Ti(IV) single atoms on
the Zr-MOF MOF-808. We reveal that upon binding of the nerve agent
to the catalyst, conformational isomerism leads to a great diversity
of hydrolysis reaction mechanisms. Each mechanism follows an addition–elimination
sequence but differs markedly in the way the elimination step is accomplished
and its energetics. Moreover, while most of the prior work has focused
on the HF elimination channel, this work shows that the addition–elimination
steps can also lead to isopropanol formation through barriers comparable
to those of the HF channel. Additional insight is achieved by high-level
electronic structure calculations, including coupled-cluster theory,
which allow us to benchmark more efficient DFT techniques commonly
used in mechanistic studies of catalytic processes involving transition-metal
atoms. Overall, this work reveals new reaction pathways for nerve-agent
hydrolysis with lower-lying transition-state energies than previously
reported, highlighting the importance of conformational sampling in
mechanistic studies of catalytic processes.