3 research outputs found
Polyyne Rotaxanes: Stabilization by Encapsulation
Active metal template Glaser coupling
has been used to synthesize
a series of rotaxanes consisting of a polyyne, with up to 24 contiguous <i>sp-</i>hybridized carbon atoms, threaded through a variety of
macrocycles. Cadiot–Chodkiewicz cross-coupling affords higher
yields of rotaxanes than homocoupling. This methodology has been used
to prepare [3]Ârotaxanes with two polyyne chains locked through the
same macrocycle. The crystal structure of one of these [3]Ârotaxanes
shows that there is extremely close contact between the central carbon
atoms of the threaded hexayne chains (C···C distance
3.29 Ă… vs 3.4 Ă… for the sum of van der Waals radii) and
that the bond-length-alternation is perturbed in the vicinity of this
contact. However, despite the close interaction between the hexayne
chains, the [3]Ârotaxane is remarkably stable under ambient conditions,
probably because the two polyynes adopt a crossed geometry. In the
solid state, the angle between the two polyyne chains is 74°,
and this crossed geometry appears to be dictated by the bulk of the
“supertrityl” end groups. Several rotaxanes have been
synthesized to explore gem-dibromoethene moieties as “masked”
polyynes. However, the reductive Fritsch–Buttenberg–Wiechell
rearrangement to form the desired polyyne rotaxanes has not yet been
achieved. X-ray crystallographic analysis on six [2]Ârotaxanes and
two [3]Ârotaxanes provides insight into the noncovalent interactions
in these systems. Differential scanning calorimetry (DSC) reveals
that the longer polyyne rotaxanes (C16, C18, and C24) decompose at
higher temperatures than the corresponding unthreaded polyyne axles.
The stability enhancement increases as the polyyne becomes longer,
reaching 60 °C in the C24 rotaxane
Synthesis of Polyyne Rotaxanes
Active-metal templating has been used to synthesize rotaxanes consisting of a phenanthroline-based macrocycle threaded around a C8, C12, or C20 polyyne chain. The crystal structure of the C12 rotaxane has been determined. In the rhenium(I) carbonyl complex of this rotaxane, with Re(CO)<sub>3</sub>Cl coordinated to the phenanthroline macrocycle, the proximity of the polyyne chain quenches the luminescence of the rhenium. These rotaxanes offer a new approach to controlling the environment and interactions of a polyyne chain
Synthesis of Polyyne Rotaxanes
Active-metal templating has been used to synthesize rotaxanes consisting of a phenanthroline-based macrocycle threaded around a C8, C12, or C20 polyyne chain. The crystal structure of the C12 rotaxane has been determined. In the rhenium(I) carbonyl complex of this rotaxane, with Re(CO)<sub>3</sub>Cl coordinated to the phenanthroline macrocycle, the proximity of the polyyne chain quenches the luminescence of the rhenium. These rotaxanes offer a new approach to controlling the environment and interactions of a polyyne chain