Reaktive E=C (p-p)π-Systeme, XL. / Reactive E=C(p-p)π Systems, XL.

The reaction of bis(trifluoromethyl)arsane 2 with secondary amines R₂NH in a molar ratio of 1:3 at -60 °C allows the preparation of trifluoromethyl arsaalkenes of the type F₃CAs=C(F)NR₂ in moderate yields (15-35%) [NR₂ = NMe₂ (3a), NMeEt (3b), NEt₂ (3c)]. The main product of the reaction of 2 with Me₂NH is the 1,1-diamino compound F₃CAs=C(NMe₂)₂ (4a). With ethyl(isopropyl)- or di(isopropyl)amine the corresponding derivatives F₃CAs=C(F)NEt(iPr) (3d) and F₃CAs=C(F)N(iPr)₂ (3e), respectively, are formed only in traces (3d), or not at all (3 e). 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 1-(diethylamino)-1,3,3,3-tetrafluoro-2-arsapropene 3c, 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 Å), an elongated AsC distance (1.867 Å), and an almost planar skeleton of the molecule.