Slipped ring complexes

Each of the sandwich compounds forms two isomers, described as clockwise and counterclockwise, respectively. Clockwise means that the atomic sequence in both rings is the same, counterclockwise that the atomic sequence is opposite. The syntheses occur best in THE at -78°C. After warming, the solvent is removed. Purification can be carried out by crystallization from petroleum, ether or better by sublimation at 60-70°C and 10 torr. The yields vary between 25 and 85%. The 17-and 18-electron complexes with V and Fe atoms show the metal atoms to be fixed above and below the ring centers. In contrast, the 19- and 20-electron complexes of Co and Ni possess slipped rings. 

As the five-electron donor converts to a one-electron donor. Re accepts an additional four electrons from the two trimethylphosphine ligands. One additional mole of PMcj causes loss of Cp from the metal. It is highly likely that the 77 -Cp complex is an intermediate in the reaction although it was not detected. When Cp ligands are found coordinated in arrangements other than the symmetric we sometimes refer to them as slipped ring systems. The rhenium reaction is an extreme example in which the ring has been induced to slip completely off the metal atom rf n Thus... 

These end groups were removed by cleaving the C-N bond with a strong base (25% NaOH) so that the CD rings may slip off the polymer chains, and the number of CDs per polyrotaxane was estimated by H NMR, optical rotation, and UV absorption to be 12. This figure indicates that nearly the entire length of the 28 mer PEG chain was covered with CDs, because, as repeatedly noted above, the stoichiometric ratio for the complexation between PEG and a-CD is 2. 

The addition of the second methyl group on the phenol ring led to the observation of the consecutive inclusion process with a decrease in the dynamics for complex formation (Table 8, cf. 29 with 28 (R = CH3)). This result supports the previous suggestion190 that small guests can slip into the CD cavity and in one process form the stable host-guest complex. 

It can be concluded that significant differences in metal-carbon bond distances to coordinated olefins are not reflected in either the slip parameter or the barrier to rotation of the indenyl ring in this series of complexes. However, the relative strengths of the interactions between the [Rh( /5-indenyl)] fragment and OFCOT and COT are illustrated by some reactivity comparisons in Section VIII,F,2. 

These complexes of catenands are remarkably stable. However, treatment of the complex with cyanide results in demetallation and the formation of the free catenane, in which the two macrocyclic ligands are still interlocked. There is a conformational change upon demetallation and in the solid state the rings have slipped . It is not trivial to estab-... 

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