THE FLUXIONAL CHARACTER OF (ETA(5)-C5H5)FE(CO)(2)(ETA(1)-C9H7) - EVIDENCE FOR THE [4-SUBSTITUTED ISOINDENE WITH TETRACYANOETHYLENE(2]CYCLOADDITION OF A METAL)

The variable-temperature NMR spectra of eta(5)-cyclopentadienyl)Fe(CO) (2)(eta(1)-indenyl), 1, do not exhibit noticeable line-broadening belo w 70 degrees C, at which point decarbonylation to yield benzoferrocene , 8, is rapid. Nevertheless, 2D-EXSY data show clearly that 1 is indee d fluxional; it undergoes successive [1,5] shifts with an activation e nergy of similar to 20 kcal mol(-1). Contrary to an earlier report, th e intermediate isoindene, 2, is sufficiently long-lived to yield a cry stallographically-characterized [4 + 2] (cyloadduct, 10, with tetracya noethylene.