Ammonium Ion Binding with Pyridine-Containing Crown Ethers

Abstract

Dipyrido[24]crown-8 (DP24C8) has been synthesized and shown to form [2]pseudorotaxanes spontaneously with dibenzylammonium ions. These complexes, which have been demonstrated by (1)H NMR spectroscopy to form faster in solution than when the macrocyclic polyether is dibenzo[24]crown-8 (DB24C8), are also stronger than their DB24C8 counterparts. One of the [2]pseudorotaxanes has been used to construct a [2]rotaxane (see above) comprising a dumbbell-shaped component based on a dibenzylammonium ion which is encircled by a DP24C8 macrocycle and terminated by (triphenylphosphonium)methyl stoppers.

Templated Synthesis of Interlocked Molecules

“…Finally, K eff values for [2]rotaxanes containing pyridine or furan units are similar for each dumbbell-shaped ion and are comparable to the strengths of binding in CD 3 CN of disubstituted dibenzylammonium salts with the crown ethers DB24C8 [118,[196][197][198] and dipyridyl [24]crown-8 [199].…”

Recent Advances in the Synthesis of Ammonium-Based Rotaxanes

“…Thus, Stoddart et al used the Wittig reaction between a pre-rotaxane bearing a triphenylphosphonium stopper and a bulky moiety bearing aldehyde [27][28][29] (scheme 6).…”

“…The first step of this synthesis was to form the pre-rotaxane 1-H•2PF 6 from the bromobenzyl derivative of the rod, DB24C8 and PPh 3 [27,29]. Then, 1-H•2PF 6 was treated with NaH as a base followed by a bulky benzaldehyde derivative.…”

Hydrogen-Bond-Mediated Template Synthesis of Rotaxanes, Catenanes, and Knotanes

“…In a simple S N 1 reaction, bulky stoppers are thus attached (Fig. 9d) [93][94][95]. The triphenyl phosphonium stoppers can then be further exchanged with other stopper aldehydes in Wittig reactions opening a wide field of different accessible axle structures with a large variety of properties [96].…”