The in, out Asymmetric Pseudo-Triple Helical Form of a D_3h Diaza-Macropentacycle

Abstract

A sterically encumbered [N(2)S(6)] macropentacycle (5) related to diazamacrobicycles and cryptands has been synthesized in 53% yield by the [1+1] condensation reaction between functionalized macrocyclic and macrotricyclic precursors. A macrononacycle (18) resulting from the corresponding [2+2] condensation was isolated in 7% yield from the reaction mixture. Both compounds showed broad features in their room-temperature (1)H NMR spectra, but their maximal average symmetry (D(3h) and D(2h), respectively) was achieved at high temperature (380 K). At low temperature (200 K, CD(2)Cl(2) solution), the macropentacycle is "frozen" to a single asymmetric (C1) conformation on the (1)H NMR time scale, which has also the molecular structure observed in the solid state by X-ray crystallography: pseudo-triple helical ( not equalC(3)) shape, io (in, out) form resulting from the endo/exo configuration at the nitrogen bridgehead atoms, and similar orientations of the tosyl substituents. The solution dynamics of the molecule can be described by coupled bridgehead nitrogen inversion, triple helix symmetrization, and reversal of triple helix handedness, with DeltaGc = 54.2 kJ mol(-1) in CD(2)Cl(2) at 300 K. Adoption of the io form by macropentacycle 5 in the crystal and in solution at low-temperature most probably results from the steric crowding and strain introduced by the [15]ane-N(2)S(2) macrocyclic bridging subunits.

Expanded Mercaptocalixarenes: A New Kind of Macrocyclic Ligands for Stabilization of Polynuclear Thiolate Clusters

“…Finally, reductive S−C bond cleavage with Na/NH 3 followed by acidic work‐up provided the hydrochloride salts of the deprotected mercaptocalix[4]arene ligands H 4 8 and H 4 9 as air‐sensitive yellow powders. Tetrathiol H 4 12 was obtained in two steps from the known macrotricycle 10 , [29d] in which the propanediamine bridges bear tosyl protecting groups and the thiophenol moieties are protected as ethylene‐bridged bis‐thioethers, as in compounds 6 and 7 . The tosyl substituents were removed by reaction of 10 with a large excess of phenol in 33 % aqueous HBr in acetic acid at 50 °C, which, after 36 h reaction, afforded macrotricycle 11 in 70 % yield after basification of the reaction mixture and extraction into dichloromethane.…”

“… Synthesis of the mercaptothiacalix[4]arene H 4 12 from the known macrotricycle 10 [29d] via the intermediate macrotricycle 11 .…”

“…The X‐ray molecular structure of 11 ⋅2CF 3 CO 2 H showed that the macrotricycle had a calix[4]arene‐like 1,2‐alternate conformation with an inversion center, and that each equivalent subunit of the molecule nested a trifluoroacetate anion, which was bound to both protonated bridgehead nitrogen atoms (Figure 7). [29d] …”

“… ORTEP view of the X‐ray molecular structure of the 1 : 2 adduct 11 ⋅2CF 3 CO 2 H of macrotricycle 11 and trifluoroacetic acid. Dashed lines represent the bifurcated hydrogen bonds between the trifluoroacetate anions and the protonated bridgehead nitrogen atoms [29d] …”

“…Materials and General Methods : Compounds 1 , [30] 5 [29a] and 10 [29d] were prepared as described in the literature. Tetrahydrofuran was dried and deoxygenated by distillation under argon over sodium/benzophenone.…”