From 2 + 2 to 8 + 8 Condensation Products of Diamine and Dialdehyde: Giant Container-Shaped Macrocycles for Multiple Anion Binding

Exploring the Spatial Arrangement of Simple 18-Membered Hexaazatetraamine Macrocyclic Ligands in Their Metal Complexes

Hexaazamacrocyclic Schiff bases have been extensively combined with lanthanoid (Ln) ions to obtain complexes with a highly axial geometry. However, the use of flexible hexaazatetraamine macrocycles containing two pyridines and acyclic spacers is rather uncommon. Accordingly, we obtained [DyL(OAc)2]OAc·7H2O·EtOH and [DyLMe2(Cl)2]Cl·2H2O, where L and LMe2 are the 18-membered macrocycles 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane and 3,10-dimethyl-3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane, respectively, which contain ethylene and methylethylene spacers between their N3 moieties. [DyL(OAc)2]OAc·7H2O·EtOH represents the first crystallographically characterized lanthanoid complex of L, while [DyLMe2(Cl)2]Cl·2H2O contributes to increasing the scarce number of LnIII compounds containing LMe2. Furthermore, the crystal structure of L·12H2O was solved, and it was compared with those of other related macrocycles previously published. Likewise, the crystal structures of the DyIII complexes were compared with those of the lanthanoid and d-metal complexes of other 18-membered N6 donor macrocycles. This comparison showed some effect of the spacers employed, as well as the influence of the size of the ancillary ligands and the metal ion. Additionally, the distinct folding behaviors of these macrocycles influenced their coordination geometries. Moreover, the luminescent properties of [DyL(OAc)2]OAc·7H2O·EtOH and [DyLMe2(Cl)2]Cl·2H2O were also investigated, showing that both complexes are fluorescent, with the emission being sensitized by the ligands.

Synthesis of a macrocyclic oligomer of pyridylbenzoxazole utilizing dynamic covalent bonds and its unsymmetric conversion

A new unsymmetric macrocycle was synthesized by an effective and high yield 3-step synthesis, which was composed of macrocyclization, irreversible conversion, and desymmetrization. The dynamic nature of imine bonds as well as selective conversion based on strain release were utilized. Moreover, the unsymmetric macrocycle formed an interesting bivalve-like 2 : 1 complex with zinc.

Hexa- and octanuclear copper(II) complexes with a tetraeicosaaza amine macrocycle

One hexa- and two octanuclear Cu(II) complexes were synthesised from different metal salts and a very large (8 + 8) tetraeicosaaza macrocycle. These nitrate, chloride and sulphate coordination compounds were characterised by taking elemental analysis, spectroscopy, crystallography and magnetic susceptibility measurements. Their crystal structures revealed different interesting coordination modes of Cu(II) cations and nuclearity in these centrosymmetric complexes. For the sulphate complex two different, homo- vs. heterochiral, arrangements of the same macrocycle L3 around the same Cu(II) cations take place.

Three modes of interactions between anions and phenolic macrocycles: a comparative study

Macrocyclic polyphenolic compounds such as resorcin[4]arenes can be considered as multidentate anion receptors. In the current work, we combine new experimental data and reports from the previous literature (solution data and deposited crystal structures from the CCDC) to systematically analyze binding motifs between resorcin[4]arene derivatives and anions, determine the role of supporting interactions from CH donors, ion pairing and estimate their relative strength. We have found that in medium polarity solvents (THF) anion binding is a main driving force for the formation of complexes between resorcinarenes and Alk₄NX salts. Three binding modes have been detected using ¹H NMR and DOSY, depending on the type of additional interactions. Mode I was observed for upper-rim unsubstituted resorcinarenes, which use OH groups and aromatic CH from the upper rim as hydrogen bond donors to form multidentate and multivalent binding sites at the upper rim. Mode II was observed for upper-rim halogenated resorcinarenes (tetrabromo- and tetraiodo-derivatives), which use OH groups and aliphatic CH atoms from the bridges to support the chelation of anions between aromatic units. This binding mode is also multidentate and multivalent, but weaker and more anion-selective than mode I (works effectively for chlorides but not for bromides). For O-substituted derivatives, mode III is observed, with anions bound in a nest formed by aromatic CH atoms in the lower rim (multidentate but monovalent binding). The relative strength of these three binding modes, their solvent-dependence, and emergence in the crystal structures (CCDC) have been evaluated.

Multinuclear Ni(II) and Cu(II) complexes of a meso 6 + 6 macrocyclic amine derived from trans-1,2-diaminocyclopentane and 2,6-diformylpyridine

Four hexanuclear chloride and sulphate Ni(II) and Cu(II) complexes 1, 2, 4 and 5 and one tetranuclear nitrate Cu(II) complex 3 have been synthesised from appropriate metal salts and 6 + 6 octadecaaza macrocyclic ligands. All obtained coordination compounds have been characterised by elemental analysis, spectroscopic methods (ESI MS, NMR and EPR), magnetic susceptibility measurements and X-ray crystallography. Their X-ray crystal structures reveal different coordination modes of metal cations involved in the obtained centro-symmetrical coordination compounds. The conformational folding of the macrocyclic ligand adopted in the respective complexes depends on the number of metal cations bound within the macrocycle but not on their type. The cavities of these multinuclear complexes might be occupied by solvent molecules and counter anions bound by hydrogen bonds or might be empty in the case where the macrocyclic ring of the ligand is squeezed in the middle. All obtained Ni(II) and Cu(II) coordination compounds are paramagnetic. This has been proved by their ¹H NMR and EPR spectra and magnetic measurements. Direct current (DC) variable-temperature magnetic susceptibility measurements on the polycrystalline samples of 1-5 were carried out in the temperature range of 1.8-300 K. The magnetic behaviour of 1 and 2 is dominated by the magnetic anisotropy of the nickel(II) ion masking the magnetic interactions between magnetic centres. The magnetic data of 3-5 reveal small antiferromagnetic interactions within the Cu₄ and Cu₆ units. EPR experiments for 3-5 show, at 9.6 and 34 GHz frequencies, that the predominant contribution to the orbitals occupied by the unpaired electrons in the ground state originates from d_x²-y².

Manganese-Catalyzed Asymmetric Formal Hydroamination of Allylic Alcohols: A Remarkable Macrocyclic Ligand Effect

A unique family of chiral peraza N₆ -macrocyclic ligands, which are conformationally rigid and have a tunable saddle-shaped cavity, is described. Utilizing their manganese(I) complexes, the first example of earth-abundant transition metal-catalyzed asymmetric formal anti-Markovnikov hydroamination of allylic alcohols was realized, providing a practical access to synthetically important chiral γ-amino alcohols in excellent yields and enantioselectivities (up to 99 % yield and 98 % ee). The single-crystal structure of a Mn^I complex indicates that the manganese atom coordinates with the chiral dialkylamine moiety in a bidentate fashion. Further DFT calculations revealed that five of the six nitrogen atoms in the ligand were engaged in multiple noncovalent interactions with Mn, an isopropanol molecule, and a β-amino ketone intermediate via coordination, hydrogen bonding, and/or CH⋅⋅⋅π interactions in the transition state, showing a remarkable role of the macrocyclic framework.

Imine- and Amine-Type Macrocycles Derived from Chiral Diamines and Aromatic Dialdehydes

The condensation of aromatic dialdehydes with chiral diamines, such as 1,2-trans-diaminocyclohexane, leads to various enantiopure or meso-type macrocyclic Schiff bases, including [2 + 2], [3 + 3], [4 + 4], [6 + 6] and [8 + 8] condensation products. Unlike most cases of macrocycle synthesis, the [3 + 3] macrocycles of this type are sometimes obtained in high yields by direct condensation without a metal template. Macrocycles of other sizes from this family can often be selectively obtained in high yields by a suitable choice of metal template, solvent, or chirality of the building blocks. In particular, the application of a cadmium(II) template results in the expansion of the [2 + 2] macrocycles into giant [6 + 6] and [8 + 8] macrocycles. These imine macrocycles can be reduced to the corresponding macrocyclic amines which can act as hosts for the binding of multiple cations or multiple anions.

Controlling chirality in the synthesis of 4 + 4 diastereomeric amine macrocycles derived from trans-1,2-diaminocyclopentane and 2,6-diformylpyridine

A few suitably long dialdehyde and primary diamine building blocks of a predetermined chirality have been designed and synthesized to enable controlled and efficient synthesis of all six possible diastereomers of 4 + 4 macrocyclic amine derived from trans-1,2-diaminocyclopentane (DACP) and 2,6-diformypyridine (DFP) units. Although two out of six diastereomers have been reported recently, their synthesis presented here is more direct and occurs with an improved yield. This family of 4 + 4 macrocycles contains one pair of homochiral enantiomers of identical RRRRRRRR and SSSSSSSS configurations of DACP units, two different meso forms (meso I of alternating RRSSRRSS and meso II of neighboring RRRRSSSS configuration of DACP moieties) as well as one pair of heterochiral enantiomers, where configuration of one diamine fragment is opposite to the other three diamine parts, RRRRRRSS and SSSSSSRR, respectively. The structures of each type of macrocycle in solid state have been confirmed by single crystal analyses of a macrocyclic amine in its suitable protonated form. The different symmetry of each type of macrocycle in solutions has been proved by ¹H and ¹³C NMR spectra of their hydrochloride derivatives. The chiral nature of two different pairs of optically active enantiomers has been established by circular dichroism spectra. These chiral 4 + 4 diastereomeric macrocycles are receptors for chiral guests and recognize in solution 10-camphorsulfonic acid as well as chiral tartaric acid.

Surface-Confined Macrocyclization via Dynamic Covalent Chemistry

Surface-confined synthesis is a promising approach to build complex molecular nanostructures including macrocycles. However, despite the recent advances in on-surface macrocyclization under ultrahigh vacuum, selective synthesis of monodisperse and multicomponent macrocycles remains a challenge. Here, we report on an on-surface formation of [6 + 6] Schiff-base macrocycles via dynamic covalent chemistry. The macrocycles form two-dimensional crystalline domains on the micrometer scale, enabled by dynamic conversion of open-chain oligomers into well-defined ∼3.0 nm hexagonal macrocycles. We further show that by tailoring the length of the alkyl substituents, it is possible to control which of three possible products-oligomers, macrocycles, or polymers-will form at the surface. In situ scanning tunneling microscopy imaging combined with density functional theory calculations and molecular dynamics simulations unravel the synergistic effect of surface confinement and solvent in leading to preferential on-surface macrocyclization.

Mixed Macrocycles Derived from 2,6-Diformylpyridine and Opposite Enantiomers of trans-1,2-Diaminocyclopentane and trans-1,2-Diaminocyclohexane

The condensation reaction of 2,6-diformylpyridine with an equimolar mixture of opposite enantiomers of trans-1,2-diaminocyclopentane and trans-1,2-diaminocyclohexane using a dynamic combinatorial chemistry approach has been examined. In nonmetal-templated reactions, depending on reaction conditions, mixed 2 + 1 + 1 macrocyclic imine or bigger mixed 4 + 2 + 2 imine macrocycle are formed selectively. The 2 + 1 + 1 imine used as a precursor in the templated by Cd^II ions produces a library of enlarged chiral mixed imines coordinated with metal cations among which the hexanuclear Cd^II complex of 6 + 3 + 3 imine was isolated and characterized. All macrocyclic imine compounds have been reduced to the corresponding macrocyclic amines, which have been further transformed into their hydrochlorides. Each macrocyclic compound has been obtained as two enantiomers. For imine macrocycles and for the hydrochloride derivatives of macrocyclic amines, their X-ray crystal structures have been determined. In particular, the crystals of protonated 4 + 2 + 2 macrocyclic amine, which contains two types of diastereomeric cations differing in terms of inverted twists of pyridine moieties, and hexanuclear Cd^II complex of 6 + 3 + 3 imine, which gives a deeper insight into the expansion reaction, have been investigated. A heterochiral self-sorting of 2 + 2 and 2 + 1 + 1 macrocyclic imines has been confirmed by a competition reaction of 2,6-diformylpyridine, racemic trans-1,2-diaminocyclopentane, and racemic trans-1,2-diaminocyclohexane and theoretical calculations.

Synthetic Evolution of the Multifarene Cavity from Planar Predecessors

The stepwise evolution of curved multifarene structures from planar precursors is demonstrated, highlighting three architectural design elements: 1) employment of various aromatic units, 2) changing the hybridization of the linking atoms from sp² to sp³ , and 3) rigidification of the system by the introduction of five-membered rings. Similar design elements have been employed to transform graphene sheets into curved carbon structures. Specifically, the stepwise synthetic evolution of multifarene[2+2], which has a curved, quite rigid structure, begins with a planar, tetraimine precursor, conversion to pairs of vicinal diamines, and the transformation of these pairs to cyclic thiourea groups. This process was probed by NMR spectroscopy and X-ray crystallography. Since varying the carbonylation conditions resulted in carbamates or thiocarbamates rather than the urea or thiourea isomers, the isomeric interconversion was studied both experimentally and by DFT computations. The carbamate versus urea preference was found to reflect either kinetic or thermodynamic control, respectively.

One-step Access to Resorcinsalens-Solvent-Dependent Synthesis, Tautomerism, Self-sorting and Supramolecular Architectures of Chiral Polyimine Analogues of Resorcinarene

Substituted 2,4- and 4,6-dihydroxyisophthalaldehydes were condensed with optically pure and racemic trans-1,2-diaminocyclohexane to form resorcinarene-like polyimine macrocycles (resorcinsalens), the structure and stoichiometry of which were controlled by the choice of the reaction medium. Particularly, the cyclocondensation reactions were driven by the solubility, tautomerization, or by social self-sorting. The resorcinsalens crystallized as inclusion compounds, in which the guest molecules were situated either in channels or in voids. In the highly hydrated crystals of one of the [2+2] macrocycles and chloroform-solvated crystals of a [4+4] product the channels were interconnected, as in zeolites, enabling possible migration of loosely bound solvent molecules in three dimensions. The association mode depended on the structural modification of the host molecule and the type of included solvent molecule(s).

Hexanuclear and Trinuclear Metal Complexes of a Giant Octadecaaza Macrocycle

A large macrocyclic ligand containing six pyridine fragments and six diaminocyclopentane fragments is able to form hexanuclear Zn(II) and Ni(II) complexes as well as a trinuclear Zn(II) complex. X-ray crystal structures of these complexes indicate quite different ligand conformations. In the hexanuclear Zn(II) derivative with chloride counteranions metal ions have a distorted-trigonal-bipyramidal geometry and occupy loop sections formed by the highly folded macrocycle, which adopts a globular shape. In the hexanuclear Ni(II) derivative with nitrate counteranions metal ions exhibit a distorted-octahedral geometry and the ligand conformation is much more open, while in the trinuclear Zn(II) complex the macrocycle wraps around the octahedral metal ions. The last highly entangled conformation of the trinuclear complex is also present in solution, as confirmed by the NOESY spectra. The NMR data indicate that the hexanuclear Zn(II) complex partially dissociates in water solutions to form the trinuclear complex, while the ¹H NMR titration of the free macrocycle with zinc(II) chloride indicates that the formation of a trinuclear complex corresponds to cooperative binding of metal ions.