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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.
Highlights
Characterization of selenium states by 77Se NMR is quite important to provide vital information for mechanism studies in organoselenium-catalyzed reactions
The situation gets worse for solid-state NMR (SSNMR) especially when the Se content is even low and more complicated factors are involved
Is used routinely in the majority of SSNMR to remove the effects of chemical shift anisotropy (CSA), to assist in the removal of heteronuclear dipolar-coupling effects, and to narrow lines from quadrupolar nuclei
Summary
Solid-state properties of the samples were initially investigated. All the polymer materials exhibit a broad reflection, indicating their amorphous structures[48]. To optimize the experimental parameters for different pulse sequences, H2SeO3 1 was first measured and used as a secondary external reference standard.
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