Formation, Structural Characterization, and Calculated NMR Chemical Shifts of Selenium-Nitrogen Compounds from SeCl4 and ArNHLi (Ar = supermesityl, mesityl)

Abstract

Supermesityl selenium diimide [Se{N(C6H2 tBu3-2,4,6)}2; Se{N(mes*)}2] can be prepared in a good yield from the reaction of SeCl4 and (mes*)NHLi. The molecule adopts an unprecedented anti,anti-conformation, as deduced by DFT calculations at PBEO/TZVP level of theory and supported by 77Se NMR spectroscopy and a crystal structure determination. An analogous reaction involving (C6H2Me3-2,4,6)NHLi [(mes)NHLi] unexpectedly lead to the reduction of selenium and afforded the selenium diamide Se{NH(mes)}2 that was characterized by X-ray crystallography and 77Se NMR spectroscopy. The Se-N bonds of 1.847(3) and 1.852(3) Å show normal single bond lengths. The <NSeN bond angle of 109.9(1) o also indicates a tetrahedral AX2E2 bonding arrangement around selenium. Two NH···N hydrogen bonds link the Se{NH(mes)}2 molecule with two discrete (mes)NH2 molecules. In the solid state selenium diamide adopts the anti-conformation, while in solution the presence of both syn- and anti-isomers could be observed. PBEO/TZVP calculations of the shielding tensors of 28 different types of selenium-containing molecules, for which the 77Se chemical shifts are unambiguously known, were carried out to assist the spectral assignment of Se{N(mes*)}2 and Se{NH(mes)}2.