Oxidative Addition to the N-C Bond Vs Formation of the Zwitterionic Intermediate in Platinum(II)-Catalyzed Intramolecular Annulation of Alkynes to Form Indoles: Mechanistic Studies and Reaction Scope.

In this study, Pt(II)-catalyzed intramolecular translocation annulation of ortho-alkynylamides to the formation of indoles is presented, where a proposed intermediacy of zwitterionic intermediate has been substantiated over the oxidative addition. We focused our attention on Pt(II)-catalyzed aminoacylation of alkynes both theoretically and experimentally using low boiling solvent where the formation of deacylation product was suppressed simultaneously. One-step intramolecular [1,3]-acyl migration from the zwitterionic intermediate is highly unlikely, which imparts a high energy barrier of +99.0 kcal mol-1. Another possible approach involving oxidative addition to the N-C bond, migratory insertion to alkyne, and subsequent reductive elimination is also explored through DFT studies to justify the reaction consequence. However, based on the computational studies, it is suggested that initial zwitterion formation is highly favored over oxidative addition. We suggest the formation of an acylium intermediate, which can further react with indol-3-ylplatinum species in an intramolecular manner, albeit within the same solvent cage to form 3-acyl indoles.

TiO2 supported cobalt oxide for olefin epoxidation reaction - characterization, catalytic activities and mechanism - using a DFT model.

Metal oxide catalysts are known to trigger C-H bond activation selectively, indicating their suitability for olefin epoxidation. Nano-structured Co3O4 supported on TiO2 was prepared for selective epoxidation of a number of olefins under optimized reaction conditions. An appropriate synthetic procedure yielded a catalytic material (Co-Ti (NP)HT) with desired crystal size and interface conditions. Incorporation of Co into the Ti matrix resulted in an enhancement in the specific surface of Ti-Co nanoparticles (77.93 m2 g-1). XPS measurements evaluated the surface cobalt atom concentration (5.77%) in Ti-Co(NP)HT, indicating more dispersion of cobalt oxide species. Catalytic application of the material, using various olefins (under optimized reaction conditions) shows higher conversion (>85%) in a 6-h time interval. The substrate : oxidant (H2O2) concentration in an optimized molar ratio of 1 : 2 shows high olefin conversion for the formation of olefin oxide. The reactivity of olefins was found to be in the order: cyclohexene > methylstyrene > styrene > chlorostyrene > p-nitrostyrene. A DFT model compared the HOMO-LUMO energies of styrene and its substituted forms. The reusability of Ti-Co (NP)HT tested up to four continuous cycles of batch operations indicates a negligible loss (0.25-0.30%) of catalytic activity.