Argentivorous Molecules Bearing Two Aromatic Side-Arms: Ag+–π and CH−π Interactions in the Solid State and in Solution

14- and 17-Membered Macrocycles Containing Amide, Amino, and Carbamate Groups in The Monocyclic Skeleton: An Accidental Byproduct Obtained from a Residue after Separation

A 14-membered cyclic compound (3) containing amide, amino, and carbamate groups, which was serendipitously obtained in the oily residue after the separation of 4-benzyl-1,4,7,10-tetraazacyldododecane-2,6-dione (2a) and 4,16-dibenzyl-1,4,7,10,13,16,19,22-octaazacyclo-tetracosane-2,6,14,18-tetraone (2b), is reported. The structure of 3 is formally a CO₂ insertion between positions 3 and 4 of the 12-membered ring in 2a. The CO₂ insertion was confirmed in the synthesis of diethyl 2,2'-(benzylazanediyl)diacetate (1) by the reaction of benzylamine with ethyl bromoacetate using K₂CO₃ as the base. In addition, the selective synthesis of 3 and ethyl N-benzyl-N-((2-ethoxy-2-oxoethoxy)carbonyl)glycinate (5) and their kinetic behavior are reported. The reaction of 5 with triethylenetetramine afforded a 17-membered macrocycle (7), which was obtained in an 18% yield. Compounds 6 and 8 were prepared from 3 and 7 by introducing benzyl groups to improve their solubility in organic solvents. Titration experiments using ¹H NMR showed that both 6 and 8 exhibit Li⁺ selectivity.

A Bridge too Far? Comparison of Transition Metal Complexes of Dibenzyltetraazamacrocycles with and without Ethylene Cross-Bridges: X-ray Crystal Structures, Kinetic Stability, and Electronic Properties

Tetraazamacrocycles, cyclic molecules with four nitrogen atoms, have long been known to produce highly stable transition metal complexes. Cross-bridging such molecules with two-carbon chains has been shown to enhance the stability of these complexes even further. This provides enough stability to use the resulting compounds in applications as diverse and demanding as aqueous, green oxidation catalysis all the way to drug molecules injected into humans. Although the stability of these compounds is believed to result from the increased rigidity and topological complexity imparted by the cross-bridge, there is insufficient experimental data to exclude other causes. In this study, standard organic and inorganic synthetic methods were used to produce unbridged dibenzyl tetraazamacrocycle complexes of Co, Ni, Cu, and Zn that are analogues of known cross-bridged tetraazamacrocycles and their transition metal complexes to allow direct comparison of molecules that are identical except for the cross-bridge. The syntheses of the known tetraazamacrocycles and the new transition metal complexes were successful with high yields and purity. Initial chemical characterization of the complexes was conducted by UV-Visible spectroscopy, while cyclic voltammetry showed more marked differences in electronic properties from bridged versions. Direct comparison studies of the unbridged and bridged compounds' kinetic stabilities, as demonstrated by decomposition using high acid concentration and elevated temperature, showed that the cyclen-based complex stability did not benefit from cross-bridging. This is likely due to poor complementarity with the Cu2+ ion while cyclam-based complexes benefited greatly. We conclude that ligand-metal complementarity must be maintained in order for the topological and rigidity constraints imparted by the cross-bridge to contribute significantly to complex robustness.

Argentivorous molecules with chromophores: dependence of their fluorescence intensities on the distance between a donor and an acceptor

We have prepared new argentivorous molecules (L2 and L3) having different linker lengths between cyclen and anthracene units. The structures of Ag⁺ complexes with the new ligands were investigated in solution and solid states. The silver(I) ion-induced ¹H NMR and UV-vis spectral changes of L2 and L3 showed the presence of 1 : 1 complexes. The solid-state structures of the Ag⁺ complexes with L2 and L3 are stable 1 : 1 complexes because four aromatic side-arms wrap the Ag⁺ incorporated in the cyclen unit. A photo-induced electron transfer (PET) effect that depends on the length of the linker connecting the nitrogen atoms of cyclen to the chromophore is also investigated. The result indicates a linear (log) correlation between the donor-chromophore average distances of the optimized structures calculated by DFT calculations and fluorescence intensities (log I), and the PET effect becomes ineffective at about 12 Å in this system.

Bis-Argentivorous Molecules Bridged by Phenyl and 4,4'-Biphenyl Groups: Structural and Dynamic Behavior of Silver Complexes

Bis-argentivorous molecules (L^a and L^b), which have phenyl and 4,4'-biphenyl groups as linkers, have been prepared. The structures of Ag⁺ complexes with the new ligands (L^a and L^b) were investigated in solution and the solid state. The CSI-MS and ¹H NMR titration of L^a and L^b with Ag⁺ show 1:1 and 1:2 complexes depending on the [Ag⁺]:[L] ratios. In the solid-state structures, single crystals of L^a and L^b with 2 equiv of Ag⁺ were prepared. X-ray crystallography of the silver(I) complexes with L^a and L^b showed that an intramolecular racemic structure (Δ(δδδδ)Λ(λλλλ) form) and a racemic mixture of Δ(δδδδ)Δ(δδδδ) and Λ(λλλλ)Λ(λλλλ) forms were formed, respectively. The dynamic ¹H NMR studies suggest the following: (i) the activation entropies (ΔS^⧧) of the side arm rotations in the Ag⁺ complex with L^a were all negative, indicating restricted rotation of the side arms due to their shortness, and (ii) the ΔS^⧧ values of the Ag⁺ complexes with L^b were negative only when the side arms of both cyclens rotated simultaneously, and the ΔS^⧧ values for the 1:1 and 1:2 complexes were positive when one cyclen side arm was rotated. These values of ΔS^⧧ indicate that the biphenyl side arms between the two cyclens are not long enough to rotate the ring freely.

Cosmosen: Octa-Armed 24-Membered Cyclic Octaamine Synthesized from a Byproduct in the Preparation of 4-Benzyl-2,6-dioxocyclen

The synthesis of an octa-armed 24-membered cyclic octaamine (1) is reported. When 4-benzyl-1,4,7,10-tetraazacyclododecane-2,6-dione (3a) was prepared by the reaction of diethylenetriamine with diethyl N-benzyliminodiacetate (2), a dimeric macrocycle (3b) was obtained as a byproduct in a 5% yield. An octa-armed 24-membered cyclic octaamine (1), named Cosmosen, was prepared via the reductive amination and reduction of 3b. The binding constants for the 1:1 and 2:1 (Ag⁺/1) complexation of 1 were estimated to be ca. 7.9 and 13.9, respectively, by titration experiments using UV-vis spectrometry in methanol and chloroform (v/v, 9:1) solutions at 298 K.

Argentivorous Molecules with Oxyethylene Chains in Side-Arms: Silver Ion-Induced Selectivity Changes toward Alkali Metal Ions

Argentivorous molecules with mono, di, tri, tetra, and penta-oxyethylene chains in aromatic side-arms were prepared (L1-L5). Titration experiments using proton nuclear magnetic resonance and cold electrospray ionization (cold-spray ionization, CSI) mass spectrometry showed that silver ions were trapped in the cyclen moiety and the arranged oxyethylene chains of the side-arms when two equivalents of silver ions were added. The silver complexes formed by adding one equivalent of silver ion to L2-L5 bind alkali metal ions using the oxyethylene chains; alkali metal ion-induced CSI mass spectral changes of L2-L5 were measured in the absence and presence of silver ions to compare the binding properties of the ligand for Li⁺, Na⁺, and K⁺ ions. As a result, the intensity ratios of [L + H + M]²⁺/[L + H]⁺ in L1-L3 were almost zero or very low. L4 and L5, which have tetra(oxyethylene) and penta(oxyethylene) chains, respectively, bind a larger size of alkali metal ions. On the other hand, in the presence of silver ions, the ratio for [L + Ag + M]²⁺/[L + H]⁺ (M = Li, Na, K) in L2-L5 was increased. The highest [L + Ag + M]²⁺/[L + H]⁺ ratios for K⁺ were observed in L4 and L5, while selectivity for Na⁺ was observed in the case of L2 and L3. These results indicate that the increased binding ability and selectivity by L2-L5 are due to the arrangement of oxyethylene chains by the conformational change of the aromatic side-arms. The Ag⁺-induced carbon-13 nuclear magnetic resonance spectral changes suggested that the second and third oxyethylene units, close to the benzene, are involved in the coordination of the second metal ion.

Argentivorous Molecules with Chromophores in Side Arms: Silver Ion-Induced Turn On and Turn Off of Fluorescence

The synthesis of argentivorous molecules (L¹ and L²) having two chromophores (4-(anthracen-9-yl)benzyl or 4-(pyren-1-yl)benzyl groups) and two benzyl groups and the fluorescence properties of their silver complexes in a solution and the solid state are reported. A crystallographic approach for the Ag⁺ complexes with L¹ and L² revealed that the observed fluorescence changes stem from the excimer formation and extinction of fluorescent. Furthermore, binding stabilities of L¹ and L² toward Ag⁺ ions were estimated by the Ag⁺-induced UV-vis and PL spectral changes.

Metallosupramolecules of pillar[5]-bis-trithiacrown including a mercury(ii) iodide ion-triplet complex

A combination of pillar[5]-bis-trithiacrown (L) and mercury(ii) halides afforded a monomer complex (Cl^--form), a 1-D coordination polymer (Br^--form) and a supramolecular ion-triplet complex [(I·Hg·I)@L] (I^--form). In the ion-triplet complex, the host encapsulates the (I^--Hg²⁺-I^-) entity via Hg²⁺π and C-HI^- interactions, reflecting geometrical complementarity.

Silver ion-induced chiral enhancement by argentivorous molecules

Optically active tetra-armed cyclens with an asymmetric chiral centre in the cyclen moiety were synthesized and were shown to enhance chirality and control of enantiomers on complexation with Ag⁺.

Inclusion of alkyl nitriles by tetra-armed cyclens with styrylmethyl groups

A new technique for the assignment of the absolute configurations of low [α]_D alkyl-nitriles using a Ag⁺ complex with a tetra-armed cyclen is reported.

C-HCl- hydrogen bonds in solution and in the solid-state: HgCl2 complexes with cyclen-based cryptands

Structural evidence is reported for C-HCl^- hydrogen bonds in solution and in the solid state of HgCl₂ complexes with cyclen-based cryptands. These cyclen-based cryptands (1) and (2) are bridged by di- and triethylene glycol units, respectively, between two aromatic rings. The X-ray structure indicates that the 2/HgCl₂ complex contains an acetonitrile molecule in the cavity.

Pre-organization of clefts for Ag-π interactions in Zn(ii) bisdipyrrin helicates for the construction of heterometallic networks

Coordination of 2,2'-bisdipyrrin based ligands to Zn(ii) cations leads to the formation of binuclear helicates with pre-organized pyrrolic strands as well as peripheral aromatic moieties for Ag-π interactions, thus affording crystalline heterometallic networks upon further interactions with Ag(i) salts without the assistance of additional heteroatom-based coordinating units.

Chemo- and Enantioselective Intramolecular Silver-Catalyzed Aziridinations

Asymmetric nitrene-transfer reactions are a powerful tool for the preparation of enantioenriched amine building blocks. Reported herein are chemo- and enantioselective silver-catalyzed aminations which transform di- and trisubstituted homoallylic carbamates into [4.1.0]-carbamate-tethered aziridines in good yields and with ee values of up to 92 %. The effects of the substrate, silver counteranion, ligand, solvent, and temperature on both the chemoselectivity and ee value were explored. Stereochemical models were proposed to rationalize the observed absolute stereochemistry of the aziridines, which undergo nucleophilic ring opening to yield enantioenriched amines with no erosion in stereochemical integrity.

Solution-Based Thermodynamically Controlled Conversion from Diblock Copolymers to Janus Nanoparticles

Nanosized polymeric Janus particles (NPJPs) have important applications in a variety of theoretical and practical research fields. However, the methods that are versatile and can prepare NPJPs highly efficiently are very limited. Herein, we reported a two-step thermodynamically controlled preparation of NPJPs with a high yield using a diblock copolymer as the precursor. At the first step, A-b-B coassembled in the solution with a partner diblock copolymer C-b-B to form the mixed shell micelles (MSMs) with B core and A/C mixed shell. Then, intramicellarly covalently cross-linking the A block chains resulted in the complete phase separation of A and C chains in the mixed shell, leading to the direct conversion of the MSMs into NPJPs. The first step, diblock copolymer micellization, is known as a thermodynamically controlled process, and we also made the second step, conversion from MSMs to NPJPs, be thermodynamically controlled due to the application of covalent cross-linking. As the result, the conversion efficiency is close to 100%. Besides, it was further confirmed that the method can be applied to different systems and used to tune the Janus balance. Therefore, this conversion should be very significant for the fabrication and application of the NPJPs.

New types of Cu and Ag clusters supported by the pyrrole-based NNN-pincer type ligand

While the neutral ligand 2,5-bis(3,5-dimethylpyrazolylmethyl)pyrrole gives the dihalide ion bridged binuclear and coordination polymers, its anionic form affords a new type of tetranuclear ‘hourglass’ shaped copper(i) and triangular silver(i) clusters owing to its increased denticity.

Sticking and patching: tuning and anchoring cyclometallated ruthenium(ii) complexes

In a series of [Ru(bpy)₂(C^N)][PF₆] complexes with a variety of functionalities in the cyclometallating ligand, the absorption response is enhanced considerably by the introduction of a 4-C₆H₄P(O)(OEt)₂ anchoring domain in the C^N pyridine ring.

Argentivorous molecules bearing three aromatic side arms: synthesis of triple-armed cyclens and their complexing property towards Ag+

Triple-armed cyclens bearing three aromatic side-arms were prepared, and the Ag⁺-ion-induced¹H NMR and UV-vis spectral changes and X-ray structures suggested that the new armed cyclens behave like an insectivorous plant (Venus flytrap).

Synthesis and structural characterization of silver(i), copper(i) coordination polymers and a helicate palladium(ii) complex of dipyrrolylmethane-based dipyrazole ligands: the effect of meso substituents on structural formation

A striking difference in the structures of silver complexes was observed because of the different substituents at the meso carbon atom of the dipyrrolylmethane-based ligand.

NHC macrometallocycles of mercury(ii) and silver(i): synthesis, structural studies and recognition of Hg(ii) complex 4 for silver ion

Seven NHC macrometallocycles (Hg(ii) and Ag(i)) were prepared, and the recognition of Ag⁺ using (NHC)₂–Hg–I₂ (4) as a host was studied.