Darstellung von (Perfluoralkyl)halogeno‐1,3‐diselenetanen aus entsprechenden Selenocarbonylfluoriden und Umsetzungen mit Bortrichlorid sowie Arsenpentafluorid¹⁾

Abstract

Preparation of (Perfluoroalkyl)halogeno‐1,3‐diselenetanes from the Corresponding Selenocarbonyl Fluorides and Reactions with Boron Trichloride or Arsenic Pentafluoride 1) Reactions of Hg(SeR t ) 2 (R t = C 2 F 5 , C 3 F 7 , CF 3 ) with (C 2 H 5 ) 2 All or All 3 in octamethylcyclotetrasiloxane produce the unstable perfluoroalkaneselenocarbonyl fluorides 1 [R 1 = CF 3 ( 1 a ), C 2 F 5 ( 1 b ), CF 3 Se ( 1 c )]. These compounds are very reactive and polymerize to rubberlike products. On heating the polymers decompose almost quantitatively to the monomers or dimers. In CFCl 3 solution 1 dimerizes at 20°C in sunlight to the corresponding cis/trans ‐1,3‐diselenetanes 2 . The structure of 2 b is determined by single crystal X‐ray diffraction. Different selenocarbonyl derivatives add to unsymmetrically substituted 1,3‐diselenetanes 3 . 1 a and 1 b react with cyclopentadiene to form the [4 + 2] cycloaddition products 4a and 4c . Halogen exchange reactions take place between 2a — d and BCl 3 . The cis ‐isomers react much faster than the trans ‐isomers to give a mixture of cis ‐, trans ‐forms of 5 . When 2c,d is treated with BCl 3 it is possible to isolate and characterize the pure trans ‐isomer 2d , which is separated by preparative gas chromatography from 5c,d . Fluorine abstraction with formation of 1,3‐diselenetan‐2‐ylium ions ( 6a — f ) are accomplished by reactions of 2 or 3 with AsF 5 in SO 2 .