The design and synthesis of two families of molecular-gear prototypes is reported, with the aim of assembling them into trains of gears on as urfacea nd ultimately achieving controlled intermolecularg earingm otion.T hese pianostool ruthenium complexes incorporate ah ydrotris(indazolyl)borate moiety as tripodalr otation axle and ap entaarylcyclopentadienyl ligand as star-shaped cogwheel, equipped with five teeth ranging from pseudo-1D aryl groups to large planar 2D paddles. Ad ivergent synthetic approach was fol-lowed,s tartingf rom ap entakis(p-bromophenyl)cyclopentadienyl ruthenium(II) complex as key precursor or from its iodinated counterpart, obtained by copper-catalyzeda romatic Br/I exchange.S ubsequent fivefold cross-couplingr eactions with various partners allowed high structurald iversity to be reacheda nd yieldedm olecular-gear prototypes with aryl-, carbazole-, BODIPY-a nd porphyrin-derived teeth of increasing size andlength.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.Scheme1.Synthesis of pentaiodinated ruthenium complex 4b starting from precursor 2a via two different routes, each involving aC u-catalyzed aromatic Finkelstein-type reaction and aligand-exchange step. -Miyaura cross-coupling reactionso fpentabrominatedp recursor 4a to yield molecular-gearp rototypes 10 and 12,incorporating BODIPY-a nd porphyrin-based paddles,respectively.

The exploitation of sunlight as a clean, renewable, and distributed energy source is key to facing the energetic demand of modern society in a sustainable and affordable fashion. In the past few decades, chemists have learned to make molecular machines, that is, synthetic chemical systems in which energy inputs cause controlled movements of molecular components that could be used to perform a task. A variety of artificial molecular machines operated by light have been constructed by implementing photochemical processes within appropriately designed (supra)molecular assemblies. These studies could open up new routes for the realization of nanostructured devices and materials capable to harness, convert, and store light energy.