Computational Exploration of Cu(II)-en Chelate Catalyzed Hydrolysis of O-isopropyl methylphosphonofluoridate

Abstract

Abstract In contrast to un-catalyzed hydrolysis of organophosphorus (OP) compounds, metal ions or/and their complexes with chelating ligands shows catalytic effects in several ways depending upon the nature of the metal, ligand, substrate and medium. It is known that Cu(II)-en chelate containing copper complexes accelerate the hydrolysis of OP compounds. However, the mechanism for this rate enhancement in the Cu(II)-en chelate catalytic hydrolysis reaction of sarin remains unexplored. We have examined possible mechanisms involving a Cu(II)-en with hydroxide nucleophile for the reaction pathway of the hydrolysis of O-isopropyl methylphosphonofluoridate (sarin) computationally. The density functional (B3LYP) employed in this study has reproduced the experimental Gibb’s free energy of activation value 15.5 kcal/mol for alkaline hydrolysis of sarin. Earlier proposal of push-pull mechanism for metal ion chelate catalyzed hydrolysis of OP compounds has been found to be unfavourable in the present study. The role of water molecules in catalyzing the hydrolysis of sarin with Cu(II)-en chelate is crucial. The catalytic process involving Cu(II)-en chelate with one water molecule is the more plausible pathway to achieve the hydrolysis of sarin with Cu(II)-en chelate complexes.