Mechanism of Olefin Rearrangements Induced by Iron Carbonyls. Rearrangements in the Bicyclo[6.1.0]nonene System

9,9-Dichlorobicyclo[6.1.0]non-4-ene (28) rearranged to the bicyclonon-3-ene isomer 29 and ultimately to bicyclonon-2-ene (30) in the presence of Fe2(CO)9. The tetracarbonyliron(0) complex of the bicyclonon-3-ene isomer (33) was isolated and subjected to similar reaction conditions but failed to produce the rearrangement product 30. Furthermore, the Fe(CO)4 complex corresponding to compound 30 did rearrange with the iron center intact, producing complex 33. These results appear to suggest that two different mechanisms are operating here, one in which an iron carbonyl species is attached to the olefin throughout the rearrangement process and the other possibly not involving intermediacy of an iron carbonyl complex. The crystal and molecular structure of complex 33 was determined by single-crystal X-ray analysis and refined by full-matrix least-squares calculations to R = 0.092 over 1420 statistically significant reflections measured by diffractometer. Crystals are triclinic, space group PĪ, a = 7.094 (4) Å, b = 16.936 (8) Å, c = 6.530 (4) Å, α = 95.49 (5)°, β = 100.16 (5)°, γ = 104.05 (5)°, U = 741.2 Å3, and Z = 2. The coordinated alkene occupies one equatorial site of a trigonal-bipyramidal iron coordination geometry, mean Fe-C(alkene) = 2.148 Å, Fe-C(carbonyl) = 1.794 Å. The cyclooctene ring is in a C5 chair-boat conformation. © 1978, American Chemical Society. All rights reserved.

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Author Andrew T. McPhail Chemistry