Reactive EC(p-p)π-systems 53 [1]: Reactivity studies on perfluoro-2-arsapropene: [2+2]-cycloaddition reactions and quantum chemical calculations

The extremely labile perfluoro-2-arsapropene F3CAs=CF2 (1) has been generated by an improved pyrolysis process of Me3SnAs(CF3)(2) and found to be stabilized by the presence of hexamethyldisiloxane and tert-butylphosphaethyne, thus allowing (i) reactivity studies with alkyne derivatives like tBuC equivalent to P, (iPr)(2)NC equivalent to P, MeC equivalent to CN(iPr)(2), HC equivalent to COEt and (ii) a full NMR investigation of 1 (F-19, C-13). Due to the instability of 1 and some of the products, the [2 + 2]-cycloaddition reactions gave the expected arsaphospha- and arsa-cyclobutene derivatives, respectively, in moderate to good yields, but in some cases contaminated with side and/or decomposition products. Unequivocal characterization of the novel compounds was accomplished by spectroscopic investigatons (H-1,C-13, F-19 ,P-31 NMR, IR, MS) supported by comparison with the data of the more stable phosphorus analogues. An interesting isomerization was observed for the 2-dialkylamino-4,4-difluoro1-trifluoromethyl-1-arsa-3-phospha-2-cyclobutenes yielding the more stable 3-dialkylamino-2,4-difluoro-1-trifluoromethyl-1-arsa-2-phospha-3-cyclobutenes. Quantum chemical calculations [B3LYP/6-311+ G(d,p)] of HAs=CH2, F3CAs=CF2, and F3CP=CF2 were carried out to compare the length of the As=C double bond with the literature data and to elucidate substituent effects on its electronic structure. (c) 2005 Wiley Periodicals, Inc.