Bis(oxofluorenediyl)oxacyclophanes: Synthesis, Crystal Structure and Complexation with Paraquat in the Gas Phase

Abstract

The first three representatives of the new family of oxacyclophanes incorporating two 2,7-dioxyfluorenone fragments, connected by [-CH(2)CH(2)O-](m) spacers (m=2-4), have been synthesized. The yield of the smallest oxacyclophane (m=2) is considerably higher with respect to the larger ones (m=3 and m=4), which are formed in comparable yields. Molecular modeling and NMR spectra analysis of the model compounds suggest that an essential difference in oxacyclophanes yields is caused by formation of quasi-cyclic intermediates, which are preorganized for macrocyclization owing to intramolecular pi-pi stacking interactions between the fluorenone units. The solid-state structures of these oxacyclophanes exhibit intra- and intermolecular pi-pi stacking interactions that dictate their rectangular shape in the fluorenone backbone and crystal packing of the molecules with the parallel or T-shape arrangement. The crystal packing in all cases is also sustained by weak C--HO hydrogen bonds. FAB mass spectral analysis of mixtures of the larger oxacyclophanes (m=3 and m=4) and a paraquat moiety revealed peaks corresponding to the loss of one and two PF(6) (-) counterions from the 1:1 complexes formed. However, no signals were observed for complexes of the paraquat moiety with the smaller oxacyclophane (m=2). Computer molecular modeling of complexes revealed a pseudorotaxane-like incorporation of the paraquat unit, sandwiched within a macrocyclic cavity between the almost parallel-aligned fluorenone rings of the larger oxacyclophanes (m=3 and m=4). In contrast to this, only external complexes of the smallest oxacyclophane (m=2) with a paraquat unit have been found in the energy window of 10 kcal mol(-1).

[2]pseudorotaxanes derived from 27‐ and 29‐membered oxaazacyclophanes and 1,2‐bis(benzimidazolium)ethane salts

“…This indicates that macrocycle OX‐3 has lower affinity for these cations than its derivative OX‐4 . The binding constants of complexes OX‐4 ⊂ 12+ and OX‐4 ⊂ 22+ were 2.3 × 10 3 and 2.4 × 10 3 M −1 , respectively, the values being comparable with those for several other [2]pseudorotaxane assemblies at similar conditions and having wheels and axles with similar features . A comparison of the binding constants for complexes OX‐4 ⊂ 12+ and OX‐4 ⊂ 22+ permits to conclude that the macrocycle has a similar affinity for the two axles, which represents an unexpected finding.…”

“…In addition to the titrations by spectroscopic methods, we performed some mass spectrometric using the ESI‐TOF technique. This technique has been used previously for the detection of pseudorotaxanes . All experiments were carried out in 1:1 (v/v) solvent mixtures of MeCN and CHCl 3 and allowed to confirm that the complexes derived from oxaazacyclophanes OX‐3 and OX‐4 and the bis(benzimidazolium) dications had 1:1 stoichiometries in solution (Table ).…”

“…Within this context, benzylammonium, benzimidazolium, and pyridinium cations have been widely used as axles to construct pseudorotaxanes and rotaxanes . Among the most frequently employed wheels are crown ethers, cyclodextrins, cucurbituril, calixarenes, and cyclophanes …”

Supramolecular Species Bearing Quaternary Azaaromatic Moieties

“…Since the number of supramolecular species bearing quaternary azaaromatic moieties is very large, [22][23][24][25][26][27][28][29][30] inclusion complexes with host molecules such as crown ethers, 31 cyclodextrins, 32-36 cucurbiturils 37,38 and calixarenes, 39,40 as well as examples of molecular elevators, 41 taco complexes 42 and cryptand-based pseudorotaxanes [43][44][45] are not described here. The references are cited starting from 2005.…”

Synthesis and properties of first representatives of crownophanes containing the f luorenone and naphthalene fragments

“…Because of this, cyclophanes are widely used in membrane transport and as catalysts, sen sors, and components of catenanes and rotaxanes that are prototypes of molecular machines and nanoelectronic devices. 7- 15 Recently, [16][17][18][19][20][21][22] we have described the syntheses and properties of first representatives of fluorenonophanes containing two fluorenone fragments or the fluorenone and stilbene fragments linked by flexible polyether chains or conformationally rigid p xylylene bridges. We have demonstrated that fluorenonophanes form stable inclu sion complexes with electron deficient organic mol ecules 16-20 and are promising templates for self assembly of [2]catenanes on their basis.…”