From Molecular Gyroscopes to Homeomorphic Isomerization: Molecules that Turn Themselves Inside-Out

Children never cease to be fascinated by toy gyroscopes, which commonly consist of (1) a rotating axis and disk, and (2) two to four spokes that connect the termini of the axis. This talk will describe syntheses of molecules that duplicate the connectivity, symmetry, and rotational ability of such gyroscopes. Complexes with trans R₃P-ML_n -PR3 linkages are first prepared, with R groups that terminate with a CH=CH₂ moiety. Then alkene metathesis followed by hydrogenation is used to construct three-spoked cage molecules. Square planar, trigonal bipyramidal, and octahedral systems can be prepared.

Certain complexes can be demetallated to yield dibridgehead diphosphines, which can exist as three stereoisomers (phosphorus lone pairs in/in, out/out, or in/out). This provides a starting point for another very interesting story. It has proved possible to show that these molecules rapidly turn themselves "inside-out" by a dynamic process that has rarely been observed previously. These topologically novel equilibria interconvert what any chemist would regard as two configurational diastereomers by purely conformational processes.

Key References

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