Lariat ethers carbon-pivot

The structure shown above is a representative of the class of lariat ethers we have called "nitrogen-pivot" compounds (31). The presence of invertable nitrogen as the point of sidearm attachment makes these compounds more flexible than the corresponding "carbon-pivot" lariat ethers (29,30). The carbon- and nitrogen-pivot lariat ethers have been prepared with a variety of sidechains attached. Examples of compounds which could be linked to existing polymers such as chloromethylated polystyrene or copolymerized with other monomers are shown below. 

Single-Armed, Carbon-Pivot Lariat Ethers... 

D.M.Dishong, C.J.Diamond, M.I.Cinoman, G.W.Gokel, Syntheses and Cation Binding Properties of Carbon Pivot Lariat Ethers, J.Am.Chem. Soc.. 105, 586 (1983). 

When the tether is attached to the macroring at carbon, the molecule is said to have a carbon pivot atom. When the side arm is attached as illustrated at the right, the pivot atom is nitrogen. Because the molecular models of these compounds resemble lassos and because the combination of side arm and macroring donors can permit a cation to be roped and tied , we have called such macrocycles lariat ethers . 

The trends are noted to be relatively similar for both the carbon-pivot and nitrogen-pivot types of lariat ethers. Binding strengths and selectivities are dependent on ring size and in general increase as ligand size increases. Strong selectivities are noted for the potassium ion, as in the crown ethers. 

We have categorized the lariat ethers according to the means by which sidearms are attached (pivot point) and how many sidearms are present The carbon-pivot compounds are more chemically stable than the nitrogen-pivot compounds but diey are inherently less flexible. The ability of nitrogen to undergo facile inversion makes the nitrogen-pivot structures generally more adaptable to a cation than is the case with carbon-pivot derivatives. Examples of lariat ether compounds are shown below. 

Lariat ethers indicate the latter are more dynamic complexers. 15-crown-5 derivatives with a methyl group attached to the pivot carbon (the carbon bearing the side-arm) bind sodium more efficiently than do the non-methyLated species. The enhanced... 

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