Reaktive EC (pp) τ-systeme: XV. Synthese und molekülstruktur des pentacarbonylchrom-komplexes von 2-(pentafluorethyl)-3-fluor-3-(trifluormethyl)-2-phosphabicyclo[2.2.1]hept-5-en

Abstract Thermolysis of Me 3 SnP(C 2 F 5 ) 2 yields only one of the two possible isomers of the phosphaalkene F 5 C 2 PC(F)CF 3 ( 1 ) and the [2 + 4] cycloaddition of 1 to cyclopentadiene again leads to only one isomeric species ( 2 ) [2]. To elucidate the structures of 1 and 2 the crystalline complex (CO) 5 Cr(C 9 H 6 F 9 P) ( 3 ) of the bicyclic phosphane 2 has been prepared by the reaction of 2 with Cr(CO) 5 THF. An X-ray diffraction study of the structure (space group P 1 ; a 8.024(6), b 9.084(6), c 14.190(1) A; α 73.62(3), β 71.20(3), γ 71.76(4)°; Z = 2) reveals that the substituents F(1) and Cr(CO) 5 in 3 occupy anti positions on the PC(6) bond, thus confirming exo -isomer structure for the cycloadduct 2 and, if a concerted mechanism for the [2 + 4] cycloaddition is assumed, Z configuration for 1 . These results are in accord with structural conclusions on the basis of 19 F NMR data.