Biogenic synthesis of δ‐MnO2 nanoparticles: A sustainable approach for C‐alkylation and quinoline synthesis via acceptorless dehydrogenation and borrowing hydrogen reactions

The sustainable and environmentally benign biogenic synthesis of manganese‐oxide nanoparticles (MnO 2 NPs) in a single crystalline δ ‐phase and its subsequent synthetic utility have been described. The synthesized δ ‐MnO 2 NPs were characterized using scanning electron microscopy (SEM), energy dispersive X‐ray (EDX), and X‐ray diffraction (XRD) analysis techniques. The detailed analysis envisages the reduction of Mn(VII) to Mn(IV) was facilitated by various phytochemicals present in the aq. mango leaves extract, avoiding the use of external ligand source. The synthesized δ ‐MnO 2 NPs were perceived in a single delta ( δ ) monoclinic crystalline phase, wherein a spherical agglomerated morphology was displayed with a particle size of <5 nm. Further, the utility of newly developed δ ‐MnO 2 NPs was showcased for alpha‐keto‐alkylation and quinoline synthesis via hydrogen autotransfer and the acceptorless dehydrogenative coupling strategy. Moreover, a series of control experiments, mechanistic elucidation, catalyst recyclability, and a dye removal study were demonstrated.