[Co (CO) (Alkynyl)] Complexes of Dibenzosuberyl and Dibenzosuberenyl Carbocations: Dibenzotropylium or Dibenzoheptafulvene?

The reaction of dibenzo[a,d]cycloheptan-5-one (dibenzosuberone) and dibenzo[a,d]cyclohept-10-en-5-one (dibenzosuberenone) with aryl- or trimethylsilylacetylides led to the formation of the corresponding alkynyldibenzosuberols and alkynyldibenzosuberenols. Treatment with dicobalt octacarbonyl and then with bis(diphenylphosphino)methane (dppm) furnished the corresponding [Co (CO) (dppm)(alkynol)] clusters 25 and 29. Upon protonation with HBF at 203 K to generate the relevant cobalt-stabilised cations, the dibenzosuberyl system 30 exhibited fluxionality such that the cation migrated between cobalt centres.