Design, syntheses, and testing of new, fullerene-wheeled single molecular nanomachines, namely, nanocars and nanotrucks, are presented. These nanovehicles are composed of three basic components that include spherical fullerene wheels, freely rotating alkynyl axles, and a molecular chassis. The use of spherical wheels based on C60 and freely rotating axles based on alkynes permits directed nanoscale rolling of the molecular structure on gold surfaces. The rolling motion observed by STM resembles the same motion performed by macroscopic entities in which rolling occurs perpendicular to the axles. A new synthesis methodology, in situ ethynylation of fullerenes, was developed for the realization of the fullerene-wheeled molecular machines. Four generations of the fullerene-wheeled structures were developed, and the latest fourth generation nanocar, 3b, along with three-wheeled triangular compounds, 4a and 4b, provided definitive evidence for fullerene-based wheel-like rolling motion, not stick-slip or sliding translation. The studies here underscore the ability to control directionality of motion in molecular-sized nanostructures through precise molecular design and synthesis.

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Homogeneous catalytic hydrogenation has played an important role in the development of modern organic synthesis. Indeed, the discovery of highly regio- and stereoselective catalysts for C=C and C=O bonds reductions has allowed the efficient synthesis of optically active compounds. As the fragrance industry has turned to synthetic ingredients to fulfill the need for novel, cost-effective, and environment-friendly products, the use of catalytic processes are more and more in demand. In this Account, we thus highlight the application of catalytic hydrogenation in the synthesis of fragrance ingredients.

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The ruthenium-catalyzed homogeneous hydrogenation of carbonyl groups has established itself as a mature synthetic method on an academic and industrial scale [1] for the selective generation of stereogenic centers as an alternative to highenergy, pyrophoric hydride reagents. The development of such catalytic systems has gone hand in hand with that of chiral bidentate diphosphine ligands, [2] which, however, are often tedious and expensive to prepare because their multistep synthesis requires air-and moisture-free conditions. In contrast, phosphine-free chiral catalysts that operate under the industrially preferred and atom-economical hydrogenation with H 2 (HY) are still rare, [3][4][5] the most successful examples being h 5 -cyclopentadienyl [3] and h 6 -arene [4] diamine Ru II complexes. Most of these catalysts, as with those operating under transfer hydrogenation (TRHY) conditions, [6] fail to match the efficiency and selectivity requirements of industrial application. Following the work carried out at Firmenich [7] on the HY of ketones with [RuCl 2 (PNNP)] catalysts, [8] where PNNP is a chiral tetradentate ligand with a P 2 N 2 donor, [9] we developed a family of ligands in which the phosphines are replaced by thioethers (SNNS). [10] Such chiral ligands are cheap, air-and moisture-stable, and easy to prepare. This is a preliminary report of ruthenium/SNNS complexes that catalyze the asymmetric HY of ketones and aldehydes with good chemo-and enantioselectivity. [10][11][12] Ligands 1 a-f (Scheme 1) were conveniently obtained in two quantitative steps without exclusion of air by nucleophilic aromatic substitution of 2-nitro-or 2-bromobenzyl aldehydes with the appropriate thiol, followed by condensation with the chiral 1,2-cyclohexanediamine. Ligand 1 g was obtained by NaBH 4 reduction of 1 a in quantitative yield. The ruthenium complexes [RuCl 2 (SNNS)] (2 a-e,g) were prepared from the reaction of [RuCl 2 (PPh 3 ) 3 ] with the appropriate tetradentate ligand (SNNS = 1 a-e,g) and were fully characterized, whereas ligand 1 f was used in situ (see below), as its complexation failed with a number of precursors. The dichloro complexes 2 a-e and 2 g are stable for several hours in CHCl 3 , toluene, and alcohol solutions when exposed to air.The crystal structure of (R,R)-[RuCl 2 (1 a)] (R,R)-(2 a) shows a weakly distorted octahedral coordination sphere around ruthenium with a trans Cl-Ru-Cl unit, and the R configuration at both Ru-thioether moieties (Figure 1).The "stepped" conformation of the tetradentate SNNS ligand is reminiscent of the achiral diimino complex trans-[RuCl 2 -(SNNS)] (SNNS = N,N'-bis(2-tert-butylthiobenzylidene)-1,3propanediamine) [11a] and of other chiral PNNP [8,13] and salen [14] analogues.