Cycloarsanes (AsCF 3 ) n (n = 4, 5) – Precursors for the Highly Reactive Diarsene F 3 CAs=AsCF 3

Tetrakis(trifluoromethyl) cyclotetraarsane (F 3 CAs) 4 ( 2 ) was used to repeat the UV initiated [4+2]‐cycloaddition reaction of the diarsene F 3 CAs=AsCF 3 ( 1 ) with cyclohexa‐1,3‐diene (CHD) and to isolate single crystals of the cycloadduct 4 for a X‐ray diffraction analysis. 4 crystallizes in the space group ${\rm P}{\bar 1}$ and contains the diarsene group in its E‐configuration. 2 was also applied for [2+2]‐cycloaddition reactions of 1 with tBuC≡P and MeC≡CN i Pr 2 , but in contrast to positive results with (F 3 CP) 4 the products were too labile for isolation. However, 2 was successfully used at room temperature as precursor for coordinating 1 as π‐donor ligand to the Pd(PPh 3 ) 2 complex fragment yielding η 2 ‐bis(trifluoromethyl)diarsene‐bis(triphenylphosphane)‐palladium(0) 5 , which was characterized by X‐ray diffraction of single crystals and by spectroscopic investigations (NMR, IR, MS). Attempts to prove the existence of the diarsene 1 , generated by different methods, by spectroscopic studies very probably failed due to its extreme reactivity, not allowing the necessary concentrations for detection. Quantum chemical calculations of the stability of 1 with respect to dimerization, the stability of the [2+2]‐cycloadduct with 1‐di(isopropyl)aminopropyne and the energy difference between 4 and the 2,3‐dimethyl‐1,3‐butadiene cycloadduct of 1 were performed to understand the considerable differences between 1 and the related diphosphene F 3 CP=PCF 3 .