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

Abstract

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.