NEW SYNTHESIS OF HYPERVALENT T-SHAPED COORDINATION-COMPOUNDS OF SELENIUM BY THE REACTION OF BIS(2-BROMOETHYL)SELENIUM DIBROMIDE WITH PYRIDINE AND ITS DERIVATIVES

The reaction of bis(2-bromoethyl)selenium dibromide 1 with pyridine 2a and its derivatives as nucleophile gave T-shaped coordination compoun ds of selenium 3a-3e with two halogen atoms in the trans positions in moderate to good yields. However, the reaction of bis(2-bromoethyl)sel enide 4 with 2a gave 1,1'-(selanediyldiethylene) dipyridin-1-ium dibro mide 5 as a normal substituted product in 42% yield. In addition, 1-(2 -selanylethyl) pyridin-1-ium bromide 11 was obtained by the reaction o f (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 H-1 NMR spectra of the compound at room temperature show ed relatively free rotation about the CH2-CH2 bond in solution.