New synthesis of hypervalent T-shaped coordination compounds of selenium by the reaction of bis(2-bromoethyl)selenium dibromide with pyridine and its derivatives

Abstract

The reaction of bis(2-bromoethyl)selenium dibromide 1 with pyridine 2a and its derivatives as nucleophile gave T-shaped coordination compounds of selenium 3a–3e with two halogen atoms in the trans positions in moderate to good yields. However, the reaction of bis(2-bromoethyl)selenide 4 with 2a gave 1,1′-(selanediyldiethylene) dipyridin-1-ium dibromide 5 as a normal substituted product in 42% yield. In addition, 1-(2-selanylethyl) pyridin-1-ium bromide 11 was obtained by the reaction of (2-bromoethyl)phenylselenium dibromide 10 with 2a in 29% yield. The crystal structures of 3a, 3b, 3d, 3e, 5 and 11 have been determined by X-ray analyses. The X-ray analysis of 11 revealed that two conformers about the CH₂–CH₂ bond exist in one crystal unit at room temperature; however, the ¹H NMR spectra of the compound at room temperature showed relatively free rotation about the CH₂–CH₂ bond in solution.