Abstract

The molecular structure of a ferrocene derivative with adjacent centers of chirality, 1,1’‐bis(tert ‐ butylphosphino)ferrocene, has been examined in the gas phase using broadband microwave spectroscopy under the isolated and cold conditions of a supersonic jet. The diastereomers of 1,1’‐bis(tert‐butylphosphino)ferrocene can adopt homo‐ and hetero‐chiral configurations, owing to the P‐chiral substituents on the cyclopentadienyl rings. Moreover, the internal ring rotation of each diastereomer gives rise to four conformers with eclipsed ring arrangements, where the two tert‐butylphosphino groups were separated by dihedral angles of approximately 72◦, 144◦, 216◦, and 288◦ with respect to the two ring centers. The interconversion barriers between the conformations are below 2 kJ/mol, whereas the pyramidal inversion of the tert‐butylphosphino groups is hindered by more than 140 kJ/mol, calculated at the B3LYP‐D3(BJ)/def2‐QZVP level of theory. In the experimental microwave spectrum, we unambiguously identified the two global‐minimum diastereomers with 72◦ conformations. The absence of other conformers can be attributed to the relaxation dynamics in the supersonic jet, which transfers the high‐energy conformers to the respective global‐minimum geometries. Additionally, we discovered that London dispersion inter‐ actions between the two tert‐butylphosphino groups play a crucial role in stabilizing the structures of this ferrocene complex.