Synthesis of substituted indazoles and their corresponding tris(indazolyl)borate tripodal ligands as key building blocks for molecular motors Review Article

The synthesis of functionalized indazoles at the 6-position of the indazole ring is developed. Such precursors give access to tris(indazolyl)borate ligands derived from the scorpionate ligands of Trofimenko. These tripodal ligands are truly bifunctional since they can coordinate a metal via the nitrogen centers of the indazolyl rings and be anchored on surfaces on the opposite side through their 6-functionalizations. Three pendant ester or thioether groups were selected to anchor metallic complexes onto, respectively, an oxide or a metallic surface in view of near-field microscopy experiments. These building blocks have been subsequently used as stator in a family of single molecular rotary motors. The architecture of such compounds is centered around half-sandwich complexes of the family of pentaphenylcyclopentadienyl hydrotris(indazolyl)borate ruthenium (II).