First Observation of a [1,7] Boron Shift—Three Independent Fluxional Processes in the Tricarbonyliron Complex of Cycloheptatrienyl(dipropyl)borane

The fluxional behavior of [1–4‐η 4 ‐ exo ‐ 7 ‐ dipropylborylcyclohepta ‐ 1,3,5‐triene]tricarbonyliron ( 14 ) has been studied by dynamic NMR. The 2 D 1 H and 13 C EXSY NMR experiments carried out at various temperatures revealed that three independent fluxional processes occur in 14 . The fastest rearrangement is a [1,7] B sigmatropic shift accompanied by [1,2] Fe migration ( E A = 71.2±2.3 kJ mol ‐1 , ln A = 32±1). Two other rearrangements also take place: [1,3] B sigmatropic and [1,3] Fe haptotropic migrations. The analysis of the observed selectivity towards [1, j ] B sigmatropic shifts ([1,3] and [1,7] B shifts are observed, but [1,5] B shifts are not) in terms of theoretical predictions gives reason to assume that the [1, j ] boron migrations occur with inversion of configuration at the migrating atom.