Expedient Synthesis of Thioether‐Functionalized Hydrotris(indazolyl)borate as an Anchoring Platform for Rotary Molecular Machines

Major improvements in the synthesis of surface‐mounted rotary molecular machines based on ruthenium(II) complexes are reported. The development of a one‐pot indium(III)‐mediated “N‐deprotection/ester reductive sulfidation” sequence allowed step economy, reproducibility and high efficiency in the synthesis of the thioether‐functionalized tripodal ligand. Switching to the thallium salt of hydrotris(indazolyl)borate and to microwave heating further optimized the preparation of the common intermediate in the modular synthesis of symmetric and dissymmetric molecular motors and gears. The penta(4‐bromophenyl)cyclopentadienyl ruthenium(II) key precursor is now reproducibly synthesized in 5 steps and 31 % overall yield on the longest linear sequence. Subsequent fivefold Suzuki–Miyaura coupling with ferroceneboronic acid led to a new C5‐symmetric pentaferrocenyl molecular motor.