Diastereoselective Self-assembly Research Articles

Diastereoselective Self-Assembly of Low-Symmetry Pdn L2n Nanocages through Coordination-Sphere Engineering.

Metal-organic cages (MOCs) are popular host architectures assembled from ligands and metal ions/nodes. Assembling structurally complex, low-symmetry MOCs with anisotropic cavities can be limited by the formation of statistical isomer libraries. We set out to investigate the use of primary coordination-sphere engineering (CSE) to bias isomer selectivity within homo- and heteroleptic Pdn L2n cages. Unexpected differences in selectivities between alternative donor groups led us to recognise the significant impact of the second coordination sphere on isomer stabilities. From this, molecular-level insight into the origins of selectivity between cis and trans diastereoisomers was gained, highlighting the importance of both host-guest and host-solvent interactions, in addition to ligand design. This detailed understanding allows precision engineering of low-symmetry MOC assemblies without wholesale redesign of the ligand framework, and fundamentally provides a theoretical scaffold for the development of stimuli-responsive, shape-shifting MOCs.

Front Cover: Chiral Self‐Sorting in Pd6L12 Metal‐Organic Cages (Chem. Asian J. 8/2023)

The origin of chiral self-sorting in the building blocks of life remains a fundamental question. Chiral self-sorting in the formation of supramolecular cages expands our understanding of the phenomenon in general. It controls the choice of the selective chiral isomer against numerous possible mixtures. This work reports chiral social self-sorting in the diastereoselective self-assembly of Pd6L12 metal-organic cages with a racemic mixture of axially chiral bis-pyridyl ligand with Pd(II) ions. More information can be found in the Research Article by Ramalingam Natarajan et al.

Diastereoselective self-assembly of a triple-stranded europium helicate with light modulated chiroptical properties.

Chiroptical photoswitches are of increasing interest for their potential in advanced information technologies. Herein, an achiral bis-β-diketonate ligand (o-L) with a photoresponsive diarylethene moiety as a linker was designed, which co-assembled with Eu3+ ions and R- and S-bis(diphenylphosphoryl)-1,10-binaphthyl (R/S-BINAPO) as chiral ancillaries to form dinuclear triple-stranded helicates, [Eu2(o-L)3(R/S-BINAPO)2]. The helicates in the enantiopure form were confirmed by 1H, 19F, 31P NMR and DOSY NMR analyses. Furthermore, the mirror-image CD and CPL spectra also demonstrate the existence of stable ground- and excited-state chiralities in solution. When exposed to alternate ultraviolet and visible light, the helicates showed reversible color variations from colorless to purple, followed by the presence of light-triggered quadruple optical and chiroptical outputs, named CD, PL, CPL and glum switches. With these light-modulated optical outputs, the possibility for the fabrication of IMPLICATION and INHIBIT logic gates was discussed.

Point Chirality Regulated Diastereoselective Self-Assembly and Circularly Polarized Luminescence in Eu(III) Triple-Stranded Helicates

Point Chirality Regulated Diastereoselective Self-Assembly and Circularly Polarized Luminescence in Eu(III) Triple-Stranded Helicates

Point Chirality Controlled Diastereoselective Self-Assembly and Circularly Polarized Luminescence in Quadruple-Stranded Europium(III) Helicates.

Aromatic β-diketones have been extensively employed as highly effective sensitizers in luminescent lanthanide complexes. However, the difficulties to make the chiral modified groups effectively participate in the frontier molecular orbital (FMO) distributions limit their applications on lanthanide circularly polarized luminescence (CPL) fields. Considering the inherent chirality of the helical structure, a pair of enantiopure dinuclear europium quadruple-stranded helicates, ΔΔ/ΛΛ-(HNEt3)2(Eu2L4) (ΔΔ/ΛΛ)-1; L = R/S-1,2-bis(4,4'-bis(4,4,4-trifluoro-1,3-dioxobutyl)phenoxyl)propane are assembled via a point chirality induced strategy. The comprehensive spectral characteristics combined with density functional theory (DFT) calculations demonstrate that the one point chirality at the spacer of the ligand successfully controls the Δ or Λ configuration around the Eu(III) ion center and the P or M helical patterns of the helicates. The mirror-image CPL and CD spectra further confirm the formation of the enantiomer pairs. As expected, the helicate presents a higher luminescence quantum yield (QY) of 68% and a large |glum| value (0.146). This study effectively combines the excellent sensitization capability of β-diketone and the helical chirality of helicates. This strategy provides an effective path for the synthesis of lanthanide material with excellent CPL performance.

Self-Assembly of Macrocyclic Boronic Esters Bearing Tellurophene Moieties and Their Guest-Responsive Phosphorescence.

Guest-controlled diastereoselective self-assembly of a diboryltellurophene and a chiral tetrol bearing an indacene backbone was achieved to give either hetero- or homochiral macrocyclic boronic esters, selectively. The heterochiral isomer (hetero-[2+2]Te ) exhibited a higher inclusion ability for electron-deficient aromatic guests, leading to effective quenching of phosphorescence from the diboryltellurophene moieties. The reported macrocycles collectively represent a promising arene sensing approach based on phosphorescence.

Chiral BINAPO-Controlled Diastereoselective Self-Assembly and Circularly Polarized Luminescence in Triple-Stranded Europium(III) Podates.

Chiral lanthanide helical architectures have received intense attentions in recent years because of their potential applications as chiral probes and sensors and as circularly polarized luminescence (CPL) materials. However, stereoselectivity control in the self-assembly of lanthanide helicate is challenging due to the poor stereochemical preference and variable coordination numbers of Ln(III) ions. Herein, we reported the employing chiral ancillary ligand R/S-BINAPO to induce achiral tripodal ligand to form a pair of homochiral lanthanide triple-helical podates [Eu(TTEA)((R/S)-BINAPO); R/S-1] {(R/S)-BINAPO = ( R/ S)-2,2'-bis(diphenylphosphoryl)-1,1'-binaphthyl; TTEA = tris[(4-(4,4,4-trifluoro-1,3-dioxobutyl)-benzamido)ethyl]amine}. X-ray crystallographic analysis for rac-1 reveals that the chirality of BINAPO is transferred during the self-assembly process to give either P or M helical architectures in podates. The 1H and 31P NMR and circular dichroism measurements confirm the diastereopurity of the assemblies in solution. A detailed optical and chiroptical characterization reveals that the luminescent enantiopure podates not only exhibit intense CPL with | glum| values reaching 0.072 but also show high luminescence quantum yields of 32.8%. Our results provide a feasible strategy for designing homochiral helical lanthanide supramolecular architecture and synthesizing excellent CPL materials.

Diastereoselective self-assembly of bisheptahelicene on Cu(111)

Stereochemical effects during two-dimensional crystallization of bisheptahelicene diastereomers on a Cu(111) surface have been studied with scanning tunnelling microscopy. The (M,M)- and (P,P)-enantiomers crystallize into a monolayer racemate lattice, whereas the (M,P)-diastereomers aggregate into their own monolayer phase.

Enantiomerically pure trinuclear helicates via diastereoselective self-assembly and characterization of their redox chemistry.

A tris(bipyridine) ligand 1 with two BINOL (BINOL = 2,2'-dihydroxy-1,1'-binaphthyl) groups has been prepared in two enantiomerically pure forms. This ligand undergoes completely diastereoselective self-assembly into D2-symmeteric double-stranded trinuclear helicates upon coordination to copper(I) and silver(I) ions and to D3-symmetric triple-stranded trinuclear helicates upon coordination to copper(II), zinc(II), and iron(II) ions as demonstrated by mass spectrometry, NMR and CD spectroscopy in combination with quantum chemical calculations and X-ray diffraction analysis. According to the calculations, the single diastereomers that are formed during the self-assembly process are strongly preferred compared to the next stable diastereomers. Due to this strong preference, the self-assembly of the helicates from racemic 1 proceeds in a completely narcissistic self-sorting manner with an extraordinary high degree of self-sorting that proves the power and reliability of this approach to achieve high-fidelity diastereoselective self-assembly via chiral self-sorting to get access to stereochemically well-defined nanoscaled objects. Furthermore, mass spectrometric methods including electron capture dissociation MS(n) experiments could be used to elucidate the redox behavior of the copper helicates.

Diastereoselective self-assembly of clofarabine lipids

Clofarabine lipids form superstructures via diastereoselective self-assembly.

Diastereoselective self-assembly of heterochiral Zn(ii) complexes of racemic Schiff bases in a chiral self-discriminating process: effect of non-covalent interactions on solid state structural self-assembly

Diastereoselective self-assembly of Zn(II) heterochiral complexes of racemic Schiff bases L1H and L2H (where L1H = 2-((phenyl(2-pyridyl)methylimino)-methyl)phenol; L2H = 1-((phenyl(2-pyridyl)methylimino)methyl)-2-naphthol) in a chiral self-discriminating process are reported. Complexes 1–6 are synthesized using ligand L1H (1–3), L2H (4–6), Zn(NO3)2·6H2O, and co-ligands such as N3− or NCS− and are conclusively structurally characterized. Determination of molecular structures of 1–5 confirmed the presence of a di-metallic core constructed by monochelated tridentate ligands with an inversion centre located directly between the two zinc ions. In 1–5, within one centrosymmetric dimer one of the ligands possessed R configuration whereas other possessed S configuration resulting a heterochiral dimerization of ligands around the Zn(II) centre in a chiral self-discriminating manner. Complex 6 is mononuclear having R configuration of ligand L2 and linked through a C–H⋯O interaction with the nearby mononuclear Zn(II) centre having S configuration of ligand L2 and consequently a heterochiral dimer. The plausible mechanism for the chiral self-discrimination is revealed which makes it clear that trans oriented anions direct the phenyl group appended to the asymmetric carbon atoms to be trans due to steric congestion and consequently the heterochiral dimerization configuration. The effects of different non-covalent interactions to self-assemble the heterochiral dimers to 1D chain having the sequence ⋯RS⋯RS⋯RS⋯ or ⋯RS⋯SR⋯RS⋯ or ⋯R⋯S⋯R⋯ and to transfer the stereochemical information of the heterochiral dimers throughout the chain are studied. Also the effects of the anions on the isotactic and syndiotactic arrangements of coordination complex are studied. The results demonstrate that ligand modification, anions and non-covalent interactions play a domino role on controlling the solid state structural rearrangements and photoluminescence properties of the synthesized complexes.

Effect of non-covalent interaction on the diastereoselective self-assembly of Cu(ii) complexes containing a racemic Schiff base in a chiral self-discriminating process

The effects of π⋯π interactions between benzene–pyridine rings on the diastereoselective self-assembly of Cu(ii) compounds in the chiral self-discrimination process are studied.

Effect of cooperative non-covalent interactions on the solid state heterochiral self-assembly: The concepts of isotactic and syndiotactic arrangements in coordination complex

Solid state diastereoselective self-assembly of five copper(II) heterochiral complexes containing racemic Schiff bases L1H and L2H (where L1H=1-((1-(2-pyridyl)ethylimino)methyl)-2-naphthol ; L2H=2-((phenyl(2-pyridyl)methylimino)-methyl)phenol) in crystal engineering contexts are discussed. Complexes 1–5 are synthesized using ligand L1H (1–3), L2H (4, 5), CuCl2·2H2O, Cu(ClO4)2·6H2O and co-ligands such as N3− or N(CN)2− and are conclusively structurally characterized. Determination of molecular structures of 1–5 confirmed the presence of a di-copper core with an inversion center located directly between the two copper ions. In 1–5, within one centrosymmetric dimer one of the ligands possess R configuration whereas other possess S configuration resulting a heterochiral dimerization of ligands around copper(II) center in chiral self-discriminating manner. The significant effects of different non-covalent interactions and co-ligands on self-assembly of heterochiral dimers into networks are studied. The presence of π⋯π interaction between face to face benzene-naphthalene and naphthalene-naphthalene dimers are perceived. The isotactic and syndiotactic arrangements of the coordination complex through non-covalent interactions are also studied.

Metal-controlled diastereoselective self-assembly and circularly polarized luminescence of a chiral heptanuclear europium wheel.

The chiral dissymmetric tetradentate ligand (S)-6'-(4-phenyloxazolin-2-yl)-2,2'-bipyridine-6-carboxylate (S-Phbipox) leads to the diastereoselective assembly of a homochiral Eu(3+) triangle and a highly emissive (quantum yield = 27%) heptanuclear wheel that is the largest example of a chiral luminescent complex of Eu(3+) reported to date. The nuclearity of the assembly is controlled by the solvent and the Eu(3+) cation. All of the compounds show large circularly polarized luminescence with an activity that varies with the nature of the assembly (highest for the homochiral trimer).

Inside Cover: Chiral Nanoscale Metal–Organic Tetrahedral Cages: Diastereoselective Self‐Assembly and Enantioselective Separation (Angew. Chem. Int. Ed. 24/2010)

The diastereoselective self-assembly of homochiral porous metal–organic tetrahedral M4L6 cages from enantiopure C2-symmetric bridging ligands (H2L) and C3-symmetric octahedral trivalent metal ions is described by Cui and co-workers in their Communication on page 4121 ff. The cages can resolve small racemic alcohols with high enantioselectivity (up to 99.5% ee) by crystallization inclusion, although kinetically stable host–guest complexes were not formed with alcohols in solution.

Chiral Nanoscale Metal-Organic Tetrahedral Cages: Diastereoselective Self-Assembly and Enantioselective Separation

Wählerisch: Chirale tetraedrische Käfige entstehen durch diastereoselektive Selbstorganisation enantiomerenreiner C2-symmetrischer Biphenylbis(β-diketonat)-Liganden und C3-symmetrischer, oktaedrisch koordinierter Fe3+- oder Ga3+-Ionen (siehe Bild; Fe violett, C blau, O rot; Hohlraum als orangefarbene Kugel). Die hohlen Polyeder zeigen ein metallabhängiges chiroptisches Verhalten und wirken als Wirt bei der Trennung racemischer Alkohole durch Kristallisation (bis 99.5 % ee). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Diastereoselective self-assembly of dinuclear heterochiral metallosupramolecular rhombs in a self-discriminating process

A racemic bis(nitrile) ligand based on the Tröger's base scaffold self-assembles into an achiral dinuclear heterochiral rhomb in a diastereoselective self-discrimination process; this occurs upon coordination to (dppp)Pd(OTf)(2) as evidenced by nmr spectroscopy and X-ray crystal structure analysis.

Chiral Confined Space: Induction of Stereochemistry in a M4L4Metallosupramolecular Container

A triangular triscatechol ligand with enantiomerically pure terminal amide groups is prepared and used for the diastereoselective self-assembly of enantiomerically pure metallosupramolecular M 4 L 4 tetrahedra.

Highly diastereoselective self-assembly of chiral tris(m-ureidobenzyl)amino capsules

The self-assembly of chiral tris(m-ureidobenzyl)amines to give dimeric capsules is a highly diastereoselective process in solution, while in the solid state, the formation of the corresponding capsules is not only diastereoselective but also regioselective.

Diastereoselective Self-Assembly of Double- and Triple-Stranded Helicates from a d-Isomannide Derivative

Difunctionalization of D-isomannide yielded a bis(bipyridine) ligand bearing four stereogenic centers whose diastereoselective self-assembly to enantiomerically pure dinuclear helicates upon coordination to different metal ions was investigated by NMR and CD spectroscopic as well as ESI mass spectrometric methods.