Gear Slippage in Molecular Bevel Gears Bridged with a Group 14 Element

Ditriptycilmethanes are known as
molecular bevel gears because
the two triptycil groups show correlated rotation. In this report, molecular bevel gears bridged with
a group 14 element, bis­(methyltriptycil)­X (X = SiH2, GeH2, GeF2), were synthesized, and their gearing properties
were investigated. Gear slippage, that is an error in gear rotation,
is observed in high-temperature solutions of molecular bevel gears.
Heavy atom derivatives undergo gear slippage more easily due to the
long bond lengths and wide angles between the two triptycil units
and the bridging group 14 element. Activation energies of gear slippages
were estimated by temperature-dependent NMR spectroscopy and DFT calculations,
and theoretical thermodynamic parameters for gear slippage were found
to be in excellent agreement with experimental values. The results
indicate that theoretical calculations for gear rotation in molecular
bevel gears can accurately reproduce experimental phenomena.