FIRST OBSERVATION OF A [1,7] BORON SHIFT - 3 INDEPENDENT FLUXIONAL PROCESSES IN THE TRICARBONYLIRON COMPLEX OF CYCLOHEPTATRIENYL(DIPROPYL)BORANE

The fluxional behavior of propylborylcyclohepta-1,3,5-triene]tricarbon yliron (14) has been studied by dynamic NMR. The 2D H-1 and C-13 EXSY NMR experiments carried out at various temperatures revealed that thre e independent fluxional processes occur in 14. The fastest rearrangeme nt is a [1,7] B sigmatropic shift accompanied by [1,2] Fe migration (E (A) = 71.2+/-2.3 kJ mol(-1), lnA = 32+/-1). Two other rearrangements a lso take place: [1,3] B sigmatropic and [1,3] Fe haptotropic migration s. The analysis of the observed selectivity towards [1,j] B sigmatropi c shifts ([1,3] and [1,7] B shifts are observed, but [1,5] B shifts ar e not) in terms of theoretical predictions gives reason to assume that the [1j] boron migrations occur with inversion of configuration at th e migrating atom.