Reaktive E=C(p-p)^-Systeme, XL. Synthese und Struktur von Arsaalkenen des Typs F3CAs=C(F)NR2

The reaction of bis(trifluoromethyl)arsane 2 with secondary amines R2NH in a molar ratio of 1:3 at -6 0 °C allows the preparation of trifluoromethyl arsaalkenes of the type F3CAs=C(F)NR2 in moderate yields (15-35% ) [NR2 = NM e2 (3a), NM eEt (3b), N Et2 (3c)]. The main product of the reaction of 2 with Me2NH is the 1,1-diamino compound F3CAs=C(NM e2)2 (4a). With ethyl(isopropyl)or di(isopropyl)amine the corresponding de­ rivatives F3CAs=C(F)NEt(/Pr) (3d) and F3CAs=C(F)N(/Pr)2 (3e), respectively, are formed only in traces (3d), or not at all (3e). However, 3d and 3e can be prepared by reacting perfluoro-2-arsapropene with the corresponding secondary amines. The new compounds 3 a to 3 e can be stored at 20 °C in chloroform solution for hours without decomposition and show Z configuration without exception. The molecular structure of l-(diethylam ino)-l,3,3,3tetrafluoro-2-arsapropene 3 c, determined by an X-ray diffraction study on single crystals, indicates a strong electronic interaction of the lone pair on nitrogen with the AsC double bond. This results in a trigonal planar arrangement at the nitrogen atom, a strongly shortened sp2-CN-bond (1.312 A ), an elongated AsC distance (1.867 Ä ), and an almost planar skeleton of the molecule.