Consecutive Oxygen-for-Sulfur Exchange Reactions between Vanadium Oxide Cluster Anions and Hydrogen Sulfide

Understanding structure-activity relation in VxOy clusters of varied stoichiometry and sizes through conceptual density functional approach

Computations have been performed on V_xO_y clusters (with x = 1-8, y = 1-21) to explore their structure, stability, and reactivity based on local and global reactivity descriptors defined within the formalism of density functional theory (DFT). The vertical and adiabatic ionization energies and electron affinities are in accordance with Franck-Condon principle and suggest that the V_xO_y clusters are more likely to be electron acceptors than donors. The structure and reactivity of V_xO_y clusters delicately depend on their oxygen content and environment. Distinct active sites have been identified for each cluster species on the basis of coordination, symmetry, and charge distribution. The propensity of all the reactive sites towards an approaching electrophile and/or nucleophile has been studied using local reactivity descriptor. In oxygen-poor clusters, the vanadium atoms are more prone to nucleophilic attack. With an increase in oxygen concentration, the coordination number of vanadium increases and reaches four-fold, the site for nucleophilic attack shifts to terminal oxygens. We conclude that of all the stoichiometries, the stable V_xO_y clusters have the (VO₃)_a(V₂O₅)_b formula unit_. The localization of positive charge density in cubic cage structure of V₈O₂₀ successfully traps halide ions (F^-, Cl^-, and Br^-). In view of increasing use of metal oxide clusters in heterogeneous catalysis, the understanding of structure-activity relationship in vanadium oxides' clusters provided in the current study is highly desirable.

Enantioselective synthesis of sulfoxide using an SBA-15 supported vanadia catalyst: a computational elucidation using a QM/MM approach

Metal catalyzed asymmetric oxidation of prochiral sulfides is one of the prevailing strategies to produce enantiopure sulfoxides. Keeping in view the reported reactivity of peroxo vanadium complexes towards asymmetric oxidation reactions, this study explores the reactivity of vanadia represented as a VO₄ cluster with CH₃-S-Ph through DFT computations. The mechanism of the oxidation of sulfides to sulfoxides with unsupported VO₄ is thoroughly investigated. The chiral centre in the VO₄ cluster is introduced by grafting it on an SBA-15 support and two conformers of the supported cluster are thus obtained. The study was extended to locate transition states for the reaction of each conformer with CH₃-S-Ph. The large enantiomeric excess obtained from the energy difference of the transition states confirms the formation of enantiopure sulfoxide. Analysis of the computational results provides a rational explanation for the observed enantioselectivity, which is remarkable. The optical stability as well as asymmetry of chiral sulfoxides obtained by the current approach has been further confirmed by locating the planar transition state, through which conversion from one enantiomer to another takes place. The calculations suggest that transition between the two enantiomers of sulfoxide is hampered by sufficiently high inversion barriers.

Reactions of metal cluster anions with inorganic and organic molecules in the gas phase

Progress on the activation and transformation of important inorganic and organic molecules by negatively charged bare metal clusters as well as ligated systems with oxygen, carbon, and nitrogen, among others.