Mechanism of isomerization of rhenium alkylidene complexes [(.eta.5-C5H5)Re(NO)(PPh3)(:CRCHR'R'')]+X- to alkene complexes [(.eta.5-C5H5)Re(NO)(PPh3)(RHC:CR'R'')]+X-: an organometallic Wagner-Meerwein-type rearrangement Academic Article uri icon

abstract

  • Propylidene complex [(η5-C6H5)Re(NO)(PPh3)(=CHCH2CH3)]+PF6− (1c+PF6−) cleanly rearranges to propene complex [(η8-C6H5)Re(NO)(PPh3)(H2C=CHCH3)]+PF6− (CeD5Cl, 65–86 °C.; ΔH* = 27 ± 1 kcal/mol; ΔS* = 3 ± 3 eu). Experiments with deuterated 1c+PF6− show a modest primary kinetic deuterium isotope effect (k(=CHCH2CH3)/k(=CHCD2CH3) = 1.95–1.40) but a considerable inverse secondary kinetic deuterium isotope effect (k(Re==CH)/k(Re==CD) = 0.50–0.58). A crossover experiment shows intramolecular hydride migration and the absence of PPh3 ligand dissociation. Optically active 1c+PF6− rearranges with retention of configuration at rhenium, but the hydride shift is not stereospecific at the migration terminus. However, the rearrangement of isobutylidene complex [(η6-C6H5)Re(NO)(PPh3)(=CHCH(CH3)2)]+SO3F− to isobutylene complex [(η5-C8H5)Re(NO)(PPh3)(H2C=C(CH3)2)]+SO3F− is highly stereoselective at the migration origin and terminus, and much faster than that of 1c+PF6− (CD2Cl2, 3–25 °C.; ΔH* = 21 ± 1 kcal/mol; ΔS* = −3 ± 3 eu). Rearrangements of analogous pentylidene and cyclopentylidene complexes are also studied. An orbital symmetry analysis of these reactions is given. © 1991, American Chemical Society. All rights reserved.

author list (cited authors)

  • Roger, C., Bodner, G. S., Hatton, W. G., & Gladysz, J. A.

citation count

  • 37

publication date

  • September 1991