Dehydrotropylium–Co 2 (CO) 6 Ion: Generation, Reactivity and Evaluation of Cation Stability

The dehydrotropylium–Co 2 (CO) 6 ion was generated by the action of HBF 4 or BF 3 ⋅ OEt 2 on the corresponding cycloheptadienynol complex, which in turn has been prepared in four steps from a known diacetoxycycloheptenyne complex. The reaction of the cycloheptadienynol complex via the dehydrotropylium–Co 2 (CO) 6 ion with several nucleophiles results in substitution reactions with reactive nucleophiles ( N >1) under normal conditions, and a radical dimerisation reaction in the presence of less reactive nucleophiles. Competitive reactions of the cycloheptadienynol complex with an acyclic trienynol complex show no preference for generation of the dehydrotropylium–Co 2 (CO) 6 ion over an acyclic cation. DFT studies on the dehydrotropylium–Co 2 (CO) 6 ion, specifically evaluation of its harmonic oscillator model of aromaticity (HOMA) value (+0.95), its homodesmotic‐reaction‐based stabilisation energy (≈2.8 kcal mol −1 ) and its NICS(1) value (−2.9), taken together with the experimental studies suggest that the dehydrotropylium–Co 2 (CO) 6 ion is weakly aromatic.