Oral 23rd International Society of Magnetic Resonance Conference 2023

The Reactivity of Open Sn Sites on Sn-β Zeolite towards MPVO Reaction: Insights from Solid state NMR Spectroscopy (#144)

Guodong Qi 1 , Weiyu Wang 1 , Jun Xu 1 , Feng Deng 1
  1. Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, HUBEI, China

Meerwein-Ponndorf-Verley reduction of aldehydes and ketones and Oppenauer’s oxidation of alcohols (MPVO reactions) are important reactions in selective reduction of carbonyl groups under mild conditions1. It has attracted wide attention in biomass upgrading2, such as the conversion sugars. The open Sn site on Sn substituted Beta (Sn-β) zeolite has been considered as the active site for many reactions, including MPVO process3. However, understanding of the role of open Sn site and involved mechanism represents a big challenge. In our previous work4, the open Sn site was directly observed by 1H/119Sn 2D correlation solid-state NMR spectroscopy. Here, we report the NMR evidence for the formation of a surface gem-diols intermediate in the MPV reduction of acetone with cyclohexanol. 

The Sn-β zeolites were synthesized by direct hydrothermal method in fluoride medium5. 1H-13C CP MAS experiments were carried out at 11.8 T on a Bruker AVANCE III 500 WB spectrometer using a 4.0 mm double-resonance probe at 12 kHz with a contact time of 4 ms and a repetition time of 2 s. In the 13C CP MAS spectra obtained from 2-13C-acetone adsorption, a strong signal at 76 ppm was observed on the low temperature dehydrated Sn-β zeolite where the open Sn sites are present. The signal at 76 ppm was suppressed when the open Sn sites were removed by high temperature dehydration, implying that the open Sn sites were responsible for formation of the signal at 76 ppm. It comes from a surface stabilized gem-diols-type species produced by OH group nucleophilic addition on 2-13C-acetone at the open Sn site. Cyclohexanol was introduced onto the Sn-β zeolite on which the gem-diols-type species was pre-produced by 2-13C-acetone. The gem-diols species was distinctly reduced to isopropyl alkoxy species at 72 ppm and isopropanol at 69 ppm. This indicates that the gem-diols species act as active intermediate in the MPVO reaction between alcohols and ketone. The result shows new insight into the property of Sn-β zeolite and the related reaction mechanism in relevance of biomass conversion.

  1. Schroeter, M., Synthetic. Commun. 35, 2203-2212 (2005).
  2. Chen, S.; Wojcieszak, R.; Dumeignil, F.; Marceau, E.; Royer, S., Chem. Rev. 118, 11023-11117 (2018).
  3. Boronat, M.; Concepcion, P.; Corma, A.; Renz, M.; Valencia, S., J. Catal. 234, 111-118 (2005).
  4. Qi, G.; Wang, Q.; Xu, J.; Wu, Q.; Wang, C.; Zhao, X.; Meng, X.; Xiao, F.; Deng, F., Communications Chemistry 1, 22 (2018).
  5. Corma, A.; Nemeth, L. T.; Renz, M.; Valencia, S., Nature 412, 423-425 (2001).