Id. Gridnev et al., FIRST OBSERVATION OF A [1,7] BORON SHIFT - 3 INDEPENDENT FLUXIONAL PROCESSES IN THE TRICARBONYLIRON COMPLEX OF CYCLOHEPTATRIENYL(DIPROPYL)BORANE, Chemistry, 2(11), 1996, pp. 1483-1488
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.