6533b836fe1ef96bd12a0814

RESEARCH PRODUCT

1H and 13C NMR investigation of the fluxional behavior of η6-(bicyclo[6.1.0]Nona-2,4,6-triene)hexacarbonyldiiron- (FeFe)

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description

Abstract The variable temperature 1 H and 13 C NMR spectra of (C 9 H 10 )Fe 2 (CO) 6 have been recorded. The molecule is fluxional. The high temperature spectra indicate an apparent plane of symmetry bisecting the bound organic ligand, whereas the low temperature limiting spectra are entirely consistent with the asymmetric skew-type structure found in the crystal. Thus the molecule is also properly described in solution as μ-(2-σ,6,7-η:35-η-bicyclo[6.1.0]nonatriene)hexacarbonyldiiron(FeFe). Based on the observed line shape changes of the carbonyl resonances between −140 and −110°C, it is shown that the twitching and not the gliding process is responsible for the relative movement of the Fe 2 (CO) 6 moiety with respect to the ring. The Δ G ≠ c for this process is found to be 7.4 kcal mol −1 , a value smaller than those previously established for the related (C 10 H 12 )- Fe 2 (CO) 6 and (C 8 H 10 )Fe 2 (CO) 6 complexes. Further carbonyl line shape changes, at higher temperatures, are only consistent with the twitch followed by local scrambling of the carbonyl groups first on the allyl-bound and then on the other iron atom, assuming that the virtually identical chemical shifts of the carbonyl resonances of this and (C 10 H 12 )Fe 2 (CO) 6 molecules can be taken to imply a correspondingly identical assignment of the respective signals. Thus it is concluded that the dynamic properties of (C 9 H 10 )Fe 2 (CO) 6 are totally analogous to those reported for (C 8 H 10 )Fe 2 (CO) 6 and (C 10 H 12 )Fe 2 (CO) 6 .