Synthesis and structure of stannane-based molecular bevel gears having substituents on a tin linker

Ditriptycylmethanes are known as molecular bevel gears because the two triptycyl groups act as wheels and display correlated rotation in solution. However, introduction of substituents on the methylene junction for chemical modification of the bevel gears has been difficult due to steric hindrance of the triptycyls. In this study, stannane-based molecular bevel gears with organic substituents on the tin linker were achieved by utilizing long Sn-C bonds. Ditriptycylstannanes with methyls or phenyls on the tin atoms were synthesized. Their structures were characterized by X-ray crystallography, and the angle of triptycyl-Sn-triptycyl in the diphenyl derivative was observed to be narrower than that of the dimethyl derivative due to steric hindrance of the phenyls. The gear rotation of these derivatives was observed by NMR spectroscopy through observations of the phase isomers of the corresponding methyltriptycyl derivatives. Gear slippage was observed in the high-temperature region, and the activation energy of the diphenyl derivative was higher than that of the dimethyl derivative. The observed relationship between gear rotation and substituents on the tin can aid in the molecular design of functional molecular bevel gears.