gem‐Diol‐Type Intermediate in the Activation of a Ketone on Sn‐β Zeolite as Studied by Solid‐State NMR Spectroscopy

Abstract

Lewis acid zeolites have found increasing application in the field of biomass conversion, in which the selective transformation of carbonyl-containing molecules is of particular importance due to their relevance in organic synthesis. Mechanistic insight into the activation of carbonyl groups on Lewis acid sites is challenging and critical for the understanding of the catalytic process,which requires the identification of reaction intermediates.H ere we report the observation of as table surface gem-diol-type species in the activation of acetone on Sn-b zeolite. 13 C, 119 Sn, and 13 C-119 Sn doubleresonance NMR spectroscopic studies demonstrate that only the open Sn site ((SiO) 3 Sn-OH) on Sn-b is responsible for the formation of the surface species. 13 CM AS NMR experiments together with density functional theory calculations suggest that the gem-diol-type species exhibits high reactivity and can serve as an active intermediate in the Meerwein-Ponndorf-Verley-Oppenauer (MPVO) reaction of acetone with cyclohexanol. The gem-diol-type species offers an energy-preferable pathway for the direct carbon-to-carbon hydrogen transfer between ketone and alcohol. The results providen ew insights into the transformation of carbonyl-containing molecules catalyzedby Lewis acid zeolites.