Thioamides: Versatile Bonds To Induce Directional and Cooperative Hydrogen Bonding in Supramolecular Polymers

Abstract

The amide bond is a versatile functional group and its directional hydrogen-bonding capabilities are widely applied in, for example, supramolecular chemistry. The potential of the thioamide bond, in contrast, is virtually unexplored as a structuring moiety in hydrogen-bonding-based self-assembling systems. We report herein the synthesis and characterisation of a new self-assembling motif comprising thioamides to induce directional hydrogen bonding. N,N',N''-Trialkylbenzene-1,3,5-tris(carbothioamide)s (thioBTAs) with either achiral or chiral side-chains have been readily obtained by treating their amide-based precursors with P2S5. The thioBTAs showed thermotropic liquid crystalline behaviour and a columnar mesophase was assigned. IR spectroscopy revealed that strong, three-fold, intermolecular hydrogen-bonding interactions stabilise the columnar structures. In apolar alkane solutions, thioBTAs self-assemble into one-dimensional, helical supramolecular polymers stabilised by three-fold hydrogen bonding. Concentration- and temperature-dependent self-assembly studies performed by using a combination of UV and CD spectroscopy demonstrated a cooperative supramolecular polymerisation mechanism and a strong amplification of supramolecular chirality. The high dipole moment of the thioamide bond in combination with the anisotropic shape of the resulting cylindrical aggregate gives rise to sufficiently strong depolarised light scattering to enable depolarised dynamic light scattering (DDLS) experiments in dilute alkane solution. The rotational and translational diffusion coefficients, D(trans) and D(rot), were obtained from the DDLS measurements, and the average length, L, and diameter, d, of the thioBTA aggregates were derived (L = 490 nm and d = 3.6 nm). These measured values are in good agreement with the value L(w) = 755 nm obtained from fitting the temperature-dependent CD data by using a recently developed equilibrium model. This experimental verification validates our common practice for determining the length of BTA-based supramolecular polymers from model fits to experimental CD data. The ability of thioamides to induce cooperative supramolecular polymerisation makes them effective and broadly applicable in supramolecular chemistry.

A metal-free and a solvent-free synthesis of thio-amides and amides: an efficient Friedel–Crafts arylation of isothiocyanates and isocyanates

“…7, 151.0, 147.6, 133.8, 120.3, 111.6, 110.4, 55.7, 55.5, 55.0, 30.7, 25.1, 24.8 8, 132.2, 127.9, 123.1, 54.8, 30.7, 25.2, 24.8, 16.6;. ESI-HRMS (m/z): Calculated for C 15 7, 148.2, 139.4, 134.8, 128.5, 128.2, 126.4, 125.1, 125.0. ESI-HRMS (m/z): Calculated for C 11 H 9 NS 2 (M + H): 220.0255, found (M + Na): 220.025.…”

N‐Substituted Benzene‐1‐Urea‐3,5‐Biscarboxamide (BUBA): Easily Accessible C2‐Symmetric Monomers for the Construction of Reversible and Chirally Amplified Helical Assemblies

“…Conversely, BUBA self‐assembly proceeds with a higher level of cooperativity and the main‐chain chirality of the resulting helices is more strongly amplified. Notably, previous modification of the BTA structure led to mitigated properties for the resulting assemblies in terms of reversibility, stability, cooperativity and chiral amplification …”

Influence of Metal, Ligand and Solvent on Supramolecular Polymerizations with Transition‐Metal Compounds: A Theoretical Study

“…[9,31] In mechanism II, an aggregate of n monomers is assembled from two smaller columns of m and x monomer units. The variation in Gibbs energy (D f G)a ssociated to each mechanistic step was calculated in the usual way,f or example, D f G (7 + 1!8) = D f H (7 + 1!8) ÀTD f S (7 + 1!8) ,w here D f H (7 + 1!8) = D f H (8) ÀD f H (7) ÀD f H (1) ,a nd D f S (7 + 1!8) = D f S (8) ÀD f S (7) ÀD f S (1) .F or each aggregate, the quantities D f H (x) and D f S (x) were calculated relative to the elements in their standard state. The heats of formation at 298 Kw ere directly obtained in the output of the MOPAC program for the geometry optimization step.…”

“…[4] The most commonly used approach to construct supramolecular self-assembled polymers is the introduction of the conventional hydrogen-bonding motif or the combination of hydrogen-bondinga nd aromatic interactions. [5][6][7] The incorporation of metals representedan ovel concept in the organization of supramolecular architectures due to the emerging metallophilic interactions, as reported by Fernµndez et al [8][9][10][11] Furthermore, other weaki nteractions such as dipole-dipole, [12] CÀH···X (X = Cl, O) interactions [10,11] and the hydrophobic effect, [13,14] when combined with aromatic interactions (also knowna sp-p stacking), can play an important role in the additional stabilization of supramolecular polymerica ssemblies.…”