Self‐Assembly of Pseudo[1]rotaxanes by Palladium(II)/Platinum(II)‐Directed Integrative Social Self‐Sorting: Is the Metal Required?

Abstract

New results are presented on the multicomponent supramolecular synthesis of pseudo[1]rotaxanes, achieved by designing pairs of structurally matching N-monoalkyl-4,4'-bipyridinium/2,7-diazapyrenium-based ligands having complementary π-donor/acceptor features, and intended to self-assemble into the targeted supramolecules by following integrative selfsorting processes. In all the studied cases, it was found that the envisioned species, characterized by NMR spectroscopy and MS spectrometry, arise as the main products of the self-assembly in aqueous media by using palladium(II)/platinum(II) metal centers as the guiding force. Crucially, we have also found that by improving the π-donor/acceptor properties of the matching pairs of ligands (L 4 and L 5), the integrative self-sorting processes prevail even in the absence of metallic ions to afford the heterodimeric species with an association constant being 756 � 43 M À 1 .

Aqueous Three-Component Self-Assembly of a Pseudo[1]rotaxane Using Hydrazone Bonds

“…Nevertheless, due to the fast exchange regime observed on the NMR timescale for all of the nuclei, no further structural information about the potential conformation of the pseudo[1]rotaxane could be obtained from the NMR data (i.e., the relative disposition of the asymmetric guest part with respect to the plane of the macrocycle). 13 Further evidence of the formation of the target species could be obtained by the corresponding DOSY experiment of S 5+ at 2.5 mM concentration, where the experimental diffusion coefficient of S 5+ (2.45 × 10 –10 m 2 /s) is comparable to that obtained theoretically from the dimensions of a local minimum found for the pseudo[1]rotaxane ( Figure 4 c, 2.32 × 10 –10 m 2 /s). 17 Likewise, HR-ESI-MS of the obtained compound also corroborated the formation of S 5+ , with m / z calculated for C 62 H 62 N 11 O 4 3+ [M – 2H] 3+ 341.4990, found: 341.4989.…”

“…The NMR data also allowed us to establish a tentative longitudinal insertion mode similar to that of 4 ⊂ F a 5+ for the naphthalene moiety within the cavity of S 5+ , as derived from the strong C–H···π interactions observed for H 3,6,7 with the short walls of the receptor, which is also reflected in the pronounced deshielding of hydrogens H a,i,j of the annulus. Nevertheless, due to the fast exchange regime observed on the NMR timescale for all of the nuclei, no further structural information about the potential conformation of the pseudo[1]­rotaxane could be obtained from the NMR data (i.e., the relative disposition of the asymmetric guest part with respect to the plane of the macrocycle) . Further evidence of the formation of the target species could be obtained by the corresponding DOSY experiment of S 5+ at 2.5 mM concentration, where the experimental diffusion coefficient of S 5+ (2.45 × 10 –10 m 2 /s) is comparable to that obtained theoretically from the dimensions of a local minimum found for the pseudo[1]­rotaxane (Figure c, 2.32 × 10 –10 m 2 /s) .…”

“…This, in turn, could be conveniently trapped by the aliphatic aldehyde 3 , which contains an ethylene glycol-based linker that would react with the appended hydrazine in F a 5+ and a naphthalene moiety that could potentially be inserted into the cavity of the macrocycle. Consequently, the addition of 3 would conveniently push the equilibrium to the smallest cyclic species since the global thermodynamic minimum, the self-inclusion complex S 5+ , would maximize the number of hydrazone bonds and intramolecular interactions per self-assembled unit. − …”

“…Encouraged by these previous results, we turned our attention to the use of the above-mentioned building blocks for the self-assembly of more complex architectures, in particular by using the mismatched reaction partners 1 a 2+ / 2 a 3+ , in combination with the aldehyde 3 , for the self-assembly of the pseudo[1]rotaxane S 5+ ( Scheme 1 ). Apart from our interest in these structurally appealing targets, 13 they have also shown utility as precursors of mechanically interlocked 14 or supramolecular daisy chains. 15 As depicted, the self-assembly of the bisaldehyde 1 a 2+ and the trishydrazine 2 a 3+ can potentially produce the [1 + 1] cyclophane F a 5+ , among other species.…”

“…Consequently, the addition of 3 would conveniently push the equilibrium to the smallest cyclic species since the global thermodynamic minimum, the self-inclusion complex S 5+ , would maximize the number of hydrazone bonds and intramolecular interactions per self-assembled unit. 13 − 15 …”