Abstract
The ring expansion reaction of cyclopentadienyl[5- exo-(α-haloalkyl)cyclopentadiene]cobalt complexes [Co(C 5H 5)(C 5H 5CRR′X) with R=CH 3, C 6H 5; R′= CH 3, C 6H 5, H; X=Cl, Br] produces 6-substituted cyclopentadienylcyclohexadienylcobalt halides. In all cases the rearrangement occurs under very mild conditions and the new cations may be isolated as hexafluorophosphates in high yields. Monosubstituted cyclopentadienylcyclohexadienylcobalt cations are formed with remarkable stereoselectivity. Thus, in the methyl series a mixture of 90% cyclopentadienyl(6 endo-methylcyclohexadienyl)cobalt cation and 10% cyclopentadienyl(6- exo-methylcyclohexadienyl)cobalt cation is obtained, whereas in the phenyl series cyclopentadienyl(6- endo-phenylcyclohexadienyl)cobalt salt is produced stereospecifically. The 1H NMR spectra and the stereochemistry of the new cations are discussed in detail.
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