An enantiomerically pure hydrogen-bonded assembly

Abstract

Chiral molecules have asymmetric arrangements of atoms, forming structures that are non-superposable mirror images of each other. Specific mirror images ('enantiomers') may be obtained either from enantiomerically pure precursor compounds, through enantioselective synthesis, or by resolution of so-called racemic mixtures of opposite enantiomers, provided that racemization (the spontaneous interconversion of enantiomers) is sufficiently slow. Non-covalent assemblies can similarly adopt chiral supramolecular structures, and if they are held together by relatively strong interactions, such as metal coordination, methods analogous to those used to obtain chiral molecules yield enantiomerically pure non-covalent products. But the resolution of assemblies formed through weak interactions, such as hydrogen-bonding, remains challenging, reflecting their lower stability and significantly higher susceptibility to racemization. Here we report the design of supramolecular structures from achiral calix[4]arene dimelamines and cyanurates, which form multiple cooperative hydrogen bonds that together provide sufficient stability to allow the isolation of enantiomerically pure assemblies. Our design strategy is based on a non-covalent 'chiral memory' concept, whereby we first use chiral barbiturates to induce the supramolecular chirality in a hydrogen-bonded assembly, and then substitute them by achiral cyanurates. The stability of the resultant chiral assemblies in benzene, a non-polar solvent not competing for hydrogen bonds, is manifested by a half-life to racemization of more than four days at room temperature.

Chemisorption‐Induced Double Hydrogen Bonding, Self‐Assembly, and Stereoselection

“…[1][2][3] The choice of molecular building blocks is based on the fundamental chemical concept of functional groups; hydrogen-bond donor-acceptor pairs have proven exceptionally useful for self-assembly. [4][5][6] Hence, it is crucial to recognize that associative chemisorption can generate hydrogen-bond donor functionality in molecules for which hydrogen bonding is negligible in the gas or solution-phase. [7,8] Herein, we report that nonsubstituted arenes form strong C À H···O hydrogen bonds to co-adsorbed esters and ketoesters on Pt(111) surfaces.…”

Coexisting Chiral Two-Dimensional Self-Assembled Structures of 1,2,3,4-Tetrahydronaphthalene Molecules: Porous Pinwheel Nanoarchitecture and Close-Packed Herringbone Arrangement

“…57 Chiral structure can also be achieved using achiral molecules. 1,54,55,58,59 In that case, the chirality results from the specific arrangement of the molecules. In the case of very small molecules made of few benzene rings, without alkyl chain and any specific substituant to drive intermolecular self-assembly, van der Waals interactions are expected to drive the formation of close-packed organic structures and the chirality of the resulting arrangements can hardly be predicted.…”

Controlling supramolecular polymerization through multicomponent self‐assembly

“…These could be reduced by the addition of what the authors call a chain terminator, a monofunctional (N-methyl)imidazolyl Znporphyrin. In the light of recent developments in manipulating the kinetic stabilities and kinetic pathways in selfassembled supramolecular complexes [128][129][130][131][132][133][134][135][136] and supramolecular polymers, 22,[30][31][32][33][34][35][36][37][38][39][40][41][42]130,[137][138][139][140][141][142][143][144][145] it is interesting to note, that the addition of the chain stopper to the polymers did not lead to instantaneous disassembly. 127 The expected depolymerization and shortening of the polymers based on the comonomer feed ratio was only observed when the di-and monofunctional comonomers were premixed in a good FIGURE 3 (a) Chemical structures for the bi-and monofunctional phosphine ligands, P(Phe) 2 C 12 (Phe) 2 P and P(Phe) 2 C 12 , in order to prepare palladium(II)-based coordination polymers.…”