From an Easily Accessible Pentacarbonylcobalt(I) Salt to Piano‐Stool Cations [(arene)Co(CO)2]

The facile synthesis of a pentacarbonyl cobalt(I) salt without the need for a superacid as solvent is presented. This salt, [Co(CO)5]+[Al(ORF)4]− {RF=C(CF3)3}, readily accessible on a multigram scale, undergoes substitution reactions with arenes yielding the hitherto unknown class of two‐legged cobalt piano‐stool complexes [(arene)Co(CO)2]+ with four different arene ligands. Such a substitution chemistry would have been impossible in superacid solution, as the arenes used would have been oxidized and/or protonated. Thus, the general approach described herein may have a wide synthetic use. Additionally, the thermochemistry of the piano‐stool complexes is shown to be not easy to describe computationally and most of the established DFT methods overestimate the reaction energies. Only CCSD(T) calculations close to the basis set limit gave energies fully agreeing with the experiment. Metal carbonyl cations go organic: The facile preparation of [Co(CO)5]+, stabilized by the weakly coordinating anion [Al(ORF)4]− {RF=C(CF3)3}, works without superacids in the organic solvent ortho‐difluorobenzene (C6H4F2). The salt can be easily isolated on a multigram scale and used for further CoI chemistry, for example, the preparation of the hitherto unknown cationic two‐legged piano‐stool carbonyl complexes [(arene)Co(CO)2]+ (arene=C6H5CH3, C6H6, C6H5F, and C6H4F2).