Desymmetrization on Both Ligands of Pentaphenylcyclopentadienylhydrotris(indazolyl) Borate Ruthenium(II) Complexes: Prototypes of Organometallic Molecular Gears and Motors

In the present review paper we present and discuss our latest contributions to the field of molecular motors and gears, exploiting half-sandwich complexes of the family of pentaphenylcyclopentadienylhydrotris(indazolyl)borate ruthenium(II) which have therefore a pseudo C5 symmetry. We will show how introducing dissymmetry in such molecular machines is very important, not only to follow the rotation of molecular gears or motors, but more importantly to induce unidirectional rotations. The article starts with our strategies to synthesize various desymmetrized complexes, desymmetrization strategies have been performed on both parts of the sandwich complex, the tris(indazolyl)borate and the pentaphenylcyclopentadienyl ligands. Finally, we present prototypes of molecular gears and to progress toward the creation of molecular devices, we report the synthesis of the tetraferrocenyl ruthenium complex, a molecular motor which has been shown to exhibit controlled clockwise or anticlockwise unidirectional rotation.