Speciation of Bulky Chiral Cyclopentadienyl Cobalt(III) Complexes: Isolation of Air-Stable 16-Electron Species

Bulky pentasubstituted chiral cyclopentadienyl ligands (CpV) were shown to form distinct species, that differ in the nature and number of auxiliary ligands, upon classical cobalt(III) complexation with Co2(CO)8 and I2. Aside from the expected and well-established coordinatively saturated CpVCo(CO)I2 architecture and its dimeric [CpVCoI2]2 derivative, the unexpected formation of monomeric 16-electron species of type CpVCoI2 was confirmed as well, thus representing a rare example of air-stable chiral half-sandwich complexes with an unsaturated 3d metal center. Herein, we report the isolation and structural characterization of these organometallic species, of which the dominant coordination mode depends on the steric encumbrance of the employed CpV ligand. All three types of CpVCo(III) speciation were analyzed by X-ray crystallography. Addition of a two-electron donor ligand, such as carbon monoxide or an isocyanide, showed that the unsaturated complexes can be converted back to 18-electron adducts.