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Organometallic
Chemistry |
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Controlling
the rotation of molecules by the construction of gears and motors
offers novel approaches to the assembly of catalysts and other nanoscale
devices. Carbon based gears have been known for some time, a result
of the pioneering work of Mislow and Iwamura who synthesised oxygen
or methylene linked triptycenes to give three-toothed bevel gears
1. To increase the number of cog-teeth available
in simple rotors, and to generate molecular gears with non-equal
gearing ratios, we became interested in the use of the cobalt metallocene
2. Here the low energy barrier to rotation of the
p-fragment about the metal is analogous to rotation about a low-friction
ball-bearing. |
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We first synthesised
3, the first example of a metallocene based molecular
gear, where the absence of a high three-fold torsional barrier common
to bridgehead substituted triptycenes is likely due to the availability
of a low energy correlated gearing mechanism between the two intermeshing
four- and three-toothed cogs.1 This is clearly evident in the X-ray structures
of 4, the related pentaphenylferrocene gear 5
[X-ray], and larger 4:3:4 gearing
arrays represented by 6.2
