Antimony bond dissociation energies

In contrast, the less strained four-7r-electron cyclopentadienyl cation is very unstable. Its p r+ has been estimated as --40, using an electrochemical cycle. The heterolytic bond dissociation energy to form the cation from cyclopentadiene is 258 kcal/mol, which is substantially more than for formation of an allylic cation from cyclopentene but only slightly more than the 252 kcal/mol for formation of an unstabilized secondary carbocation. " Solvolysis of cyclopentadienyl halides assisted by silver ion is extremely slow, even though the halide is doubly allylic. When the bromide and antimony pentafluoride react at -78°C, the EPR spectrum observed indicates that the cyclopentadienyl cation is a triplet. Similar studies indicate that pentachlorocyclopentadienyl cation is also a triplet, but the ground state of the pentaphenyl derivative is a singlet. 

Mossbauer spectroscopy has not been noted in this report for some years, so it was of some interest to find that Ishiguro and co-workers have produced Sb, Fe and spectra in a detailed study on antimony-transition metal bonds in metal carbonyl derivatives of tertiary stibines. Finally, in this section, Beyer and Leary comment on energy-resolved collision-induced dissociation of Fc2(CO)/ (y = 1-9). 

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