Supramolecular Helical Assemblies of Dirhodium(II) Paddlewheels with 1,4-Diazabicyclo[2.2.2]octane: A Remarkable Substituent Effect on the Helical Sense Preference and Amplification of the Helical Handedness Excess of Metallo-Supramolecular Helical Polymers

Abstract

We report unique coordination-driven supramolecular helical assemblies of a series of dirhodium(II) tetracarboxylate paddlewheels bearing chiral phenyl-or methyl-substituted amidebound m-terphenyl residues with triethylene glycol monomethyl ether (TEG) or n-dodecyl tails through a 1:1 complexation with 1,4-diazabicyclo[2.2.2]octane (DABCO). The chiral dirhodium complexes with DABCO in CHCl 3 /n-hexane (1:1) form onehanded helical coordination polymers with a controlled propeller chirality at the m-terphenyl groups, which are stabilized by intermolecular hydrogen-bonding networks between the adjacent amide groups at the periphery mainly via a cooperative nucleation−elongation mechanism as supported by circular dichroism (CD), vibrational CD, and variable-temperature (VT) absorption and CD analyses. The VT visible-absorption titrations revealed the temperature-dependent changes in the degree of polymerization. The columnar supramolecular helical structures were elucidated by X-ray diffraction and atomic force microscopy. The helix sense of the homopolymer carrying the bulky phenyl and n-dodecyl substituents is opposite those of other chiral homopolymers despite having the same absolute configuration at the pendants. A remarkably strong "sergeants and soldiers" (S&S) effect was observed in most of the chiral/achiral copolymers, while the copolymers of the bulky chiral phenyl-substituted dirhodium complexes with n-dodecyl chains displayed an "abnormal" S&S effect accompanied by an inversion of the helix sense, which could be switched to a "normal" S&S effect by changing the solvent composition. A nonracemic dirhodium complex of 20% enantiomeric excess bearing the less bulky chiral methyl substituents with n-dodecyl chains assembled with DABCO to form an almost onehanded helix (the "majority rule" (MR) effect), whereas the three other nonracemic copolymers showed a weak MR effect.

Rationalizing the Extent of the “Sergeants‐and‐Soldiers” Effect in Supramolecular Helical Catalysts: Effect of Copper Coordination

“…[35,36] Meijer and co-workers notably found that lowering the temperature increases the extent of the S&S effect of BTA coassemblies by increasing the mismatch penalty value. [34] In addition to the temperature, [34,[37][38][39] parameters investigated to tune the S&S effect include the chemical nature of the "sergeants" [34,[37][38][39][40][41][42][43] or the "soldiers", [41] the concentration, [34] the solvent, [44,45] a physical field, [46] and additives. [47,48] The extent of the S&S effect is correlated to the number of defects, as quantified by the energetic values associated with helix reversals and chiral mismatches.…”

Porous Supramolecular Assembly of Pentiptycene-Containing Gold(I) Complexes: Persistent Excited-State Aurophilicity and Inclusion-Induced Emission Enhancement

“…Supramolecular assembly is a powerful strategy for generating new collective properties (e.g., helicity and porosity) beyond the characteristics of individual molecules. − To construct a specific supramolecular entity, a predictable molecular assembly behavior based on the molecular structure is essential. However, the design of an extrinsic porous supramolecular framework remains to be a challenging task because the intermolecular interactions are much weaker than the coordination or covalent bonds in the well-established porous frameworks such as metal–organic frameworks and covalent organic frameworks .…”

Helical fluxionality: numerical frustration drives concerted low-barrier screw motions of a tricopper cluster

“…To build structural mimics of such constructs, helical metal-ligand assemblies have been investigated extensively. [7][8][9][10][11][12][13][14][15][16][17] Studies on metallohelicates have focused primarily on topological design, 10,[18][19][20][21] stereoselective synthesis, [22][23][24][25][26] chiroptical application, [26][27][28][29] and DNA binding properties. [30][31][32][33][34] Within this context, only a handful of works explored the dynamic aspects of helical metal complexes.…”