Solid-State 77Se NMR of Organoselenium Compounds through Cross Polarization Magic Angle Spinning (CPMAS) Method

Abstract

Characterization of selenium states by 77Se NMR is quite important to provide vital information for mechanism studies in organoselenium-catalyzed reactions. With the development of heterogeneous polymer-supported organoselenium catalysts, the solid state 77Se NMR comes to the spotlight. It is necessary to figure out an advanced protocol that provides good quality spectra within limited time because solid state 77Se NMR measurements are always time consuming due to the long relaxation time and the relatively low sensitivity. Studies on small molecules and several novel polymer-supported organoselenium materials in this article showed that cross polarization (CP) method with the assistance of magic angle spinning (MAS) was more efficient to get high quality spectra than the methods by using single pulse (SP) or high power 1H decoupling (HPHD) combined with MAS. These results lead to a good understanding of the effect of the molecular structure, the heteronuclear coupling, the long-range ordering of the solid (crystal or amorphous), and the symmetry of 77Se on quality of their spectra.

Selenium‐NMR Spectroscopy in Organic Synthesis: From Structural Characterization Toward New Investigations

“…Moreover, the non‐homogeneity of the solid sample requires higher spinning speed combined with cross‐polarization (CP) and magic angle spinning (MAS) protocols, in an attempt to afford sharper signals. In this context, recently, Yu and co‐workers have established the best experimental NMR parameters to improve the quality of the solid state 77 Se NMR spectra [140] …”

“…In this context, recently, Yu and co-workers have established the best experimental NMR parameters to improve the quality of the solid state 77 Se NMR spectra. [140] On the other hand, Ebselen is a synthetic organoselenium compound with anti-inflammatory and anti-oxidant activities. [141] Additionally, Ebselen is a prominent target for the treatment of the novel coronavirus infection (COVID-19), that emerged from Wuhan in 2019.…”

“…Considering the organoselenium chemistry, 77 Se NMR spectroscopy has become one of the most important technique to understand the structures and dynamic process, [31,32] as well as solid materials [33,34,35] . The advantages of 77 Se NMR include simplicity in the measurements, broad substrate applicability, structural and dynamic information, and the ability to analyze complex mixtures.…”

“…[29,30] Considering the organoselenium chemistry, 77 Se NMR spectroscopy has become one of the most important technique to understand the structures and dynamic process, [31,32] as well as solid materials. [33,34,35] The advantages of 77 Se NMR include simplicity in the measurements, broad substrate applicability, structural and dynamic information, and the ability to analyze complex mixtures. This review aims to summarize the recent developments on 77 Se NMR strategies, as an important auxiliary in the development of synthetic methodologies, highlighting the gain of benefits in using this approach.…”

NMR Crystallography Enhanced by Quantum Chemical Calculations and Liquid State NMR Spectroscopy for the Investigation of Se‐NHC Adducts**

“…[50] The properties of NHC systems can also be determined from 77 Se lsNMR, which operates on the relatively high natural abundance 1 = 2 spin 77 Se nuclei with the chemical shift dispersion range from approximately À 1000 to 6000 ppm. [51][52][53][54][55][56][57] In principle, the 77 Se lsNMR approach towards NHC ligands involves the investigation of the 77 Se NHC adduct, where 77 Se serves as a "spying" nucleus. [49,58] The described Se-NHC adduct methodology is further facilitated strongly by the quite straightforward synthesis of Se-NHC adducts, which are easy to handle because Se-NHC adducts are usually much less air and water sensitive.…”