Host–Guest Complexes of C‐Ethyl‐2‐methylresorcinarene and Aromatic N,N′‐Dioxides

Abstract

The C‐ethyl‐2‐methylresorcinarene (1) forms 1:1 in‐cavity complexes with aromatic N,N′‐dioxides, only if each of the aromatic rings has an N−O group. The structurally different C‐shaped 2,2′‐bipyridine N,N′‐dioxide (2,2′‐BiPyNO) and the linear rod‐shaped 4,4′‐bipyridine N,N′‐dioxide (4,4′‐BiPyNO) both form 1:1 in‐cavity complexes with the host resorcinarene in C 4v crown and C 2v conformations, respectively. In the solid state, the host–guest interactions between the 1,3‐bis(4‐pyridyl)propane N,N′‐dioxide (BiPyPNO) and the host 1 stabilize the unfavorable anti‐gauche conformation. Contrary to the N,N′‐dioxide guests, the mono‐N‐oxide guest, 4‐phenylpyridine N‐oxide (4PhPyNO), does not form an in‐cavity complex in the solid state. The host–guest complexation and the relative guest affinities were studied through 1H NMR competition experiments in methanol. Single‐crystal X‐ray crystallography of the 1:1 complexes supports the proposed solution‐state structures, also revealing strong hydrogen bonds between the host and the guests, not observed in solution owing to hydrogen/deuterium (H/D) exchange processes in methanol.

Host–guest complexes of conformationally flexibleC-hexyl-2-bromoresorcinarene and aromaticN-oxides: solid-state, solution and computational studies

“…From our experience, the lack of π-acidic aromatic protons in guest 10 usually results in exo complexes [ 36 – 37 39 ]. To our surprise, 10 +BrC6 forms a self-inclusion complex of BrC6 by itself as shown in Fig.…”

“…In reports from our lab, we disclosed that the π-acidity of aromatic protons assist in orienting the N- oxide guest by C–H···π interactions, and that the HB accepting N–O group is positioned “up”, extending out beyond the cavity to interact with solvent molecules. Our work, investigating the interactions of PyNO guests with various resorcinarene hosts, has investigated the impact of host cavity flexibility, guest’s steric and electronic demands, and solvent effects, in both solution and the solid state [ 36 – 38 ]. For example, we recently studied C -ethyl-2-bromoresorcinarene (BrC2) [ 39 ] and C -propyl-2-bromoresorcinarene (BrC3) [ 40 ] to understand the effect of the electronic nature of the host cavity core and rigidity of the resorcinarene skeleton on the ability to host various PyNO guests.…”

Bamboo-like Chained Cavities and Other Halogen-Bonded Complexes from Tetrahaloethynyl Cavitands with Simple Ditopic Halogen Bond Acceptors

“…Resorcinarenes, [29][30][31][32][33][34][35][36][37] their salts, [38][39][40][41][42][43][44] and resorcinarene cavitands [22][23][24][25][26]28,[45][46][47][48][49] are well-studied families of macrocyclic receptors. Resorcinarenes are particularly useful due to their ease of preparation, simplicity of functionalization, and versatility as hosts for a wide variety of guests.…”

“…Resorcinarenes, − their salts, − and resorcinarene cavitands − ,,− are well-studied families of macrocyclic receptors. Resorcinarenes are particularly useful due to their ease of preparation, simplicity of functionalization, and versatility as hosts for a wide variety of guests. − The known resorcinarene capsules formed through HBs, metal–ligand coordination bonds, and dynamic covalent bonds have recently been reviewed by Kobayashi and Yamanaka .…”

“…Resorcinarenes, − their salts, − and resorcinarene cavitands − ,,− are well-studied families of macrocyclic receptors. Resorcinarenes are particularly useful due to their ease of preparation, simplicity of functionalization, and versatility as hosts for a wide variety of guests. − The known resorcinarene capsules formed through HBs, metal–ligand coordination bonds, and dynamic covalent bonds have recently been reviewed by Kobayashi and Yamanaka . Concurrent with that review, we reported a novel dimeric solid-state capsule held together solely by halogen bonds (XBs) based on a preorganized tetratopic resorcinarene XB acceptor .…”