Metal‐Assisted One‐Pot Synthesis of Isoporphyrin Complexes

Zinc and cadmium complexes of meso‐arylisoporphyrins carrying a pyrrolyl or dipyrrinyl substituent at the sp³ carbon atom were obtained through a simple one‐pot variation of the Alder–Longo porphyrin synthesis. Key to the formation and stabilization of isoporphyrins is the presence of metal acetates during the oxidative macrocyclization step. The characteristic Q‐bands of isoporphyrins are found in the NIR region between 750 nm and 880 nm. All of the isolated pyrrolyl‐ and dipyrrinyl‐appended isoporphyrins are stable under typical laboratory conditions and allow chemical transformations like BF₂ coordination, transmetalation, and ligand exchange.     

Vernier‐Templated Synthesis,Crystal Structure,and Supramolecular Chemistry of a 12‐Porphyrin Nanoring

Vernier templating exploits a mismatch between the number of binding sites in a template and a reactant to direct the formation of a product that is large enough to bind several template units. Here, we present a detailed study of the Vernier‐templated synthesis of a 12‐porphyrin nanoring. NMR and small‐angle X‐ray scattering (SAXS) analyses show that Vernier complexes are formed as intermediates in the cyclo‐oligomerization reaction. UV/Vis/NIR titrations show that the three‐component assembly of the 12‐porphyrin nanoring figure‐of‐eight template complex displays high allosteric cooperativity and chelate cooperativity. This nanoring–template 1:2 complex is among the largest synthetic molecules to have been characterized by single‐crystal analysis. It crystallizes as a racemate, with an angle of 27° between the planes of the two template units. The crystal structure reveals many unexpected intramolecular C?H???N contacts involving the tert‐butyl side chains. Scanning tunneling microscopy (STM) experiments show that molecules of the 12‐porphyrin template complex can remain intact on the gold surface, although the majority of the material unfolds into the free nanoring during electrospray deposition.     

Template‐Free Synthesis of a Molecular Solomon Link by Two‐Component Self‐Assembly

A molecular Solomon link was synthesized in high yield through the template‐free, coordination‐driven self‐assembly of a carbazole‐functionalized donor and a tetracene‐based dinuclear ruthenium(II) acceptor. The doubly interlocked topology was realized by a strategically chosen ligand which was capable of participating in multiple CH ??? π and π–π interactions, as evidenced from single‐crystal X‐ray analysis and computational studies. This method is the first example of a two‐component self‐assembly of a molecular Solomon link using a directional bonding approach. The donor alone was not responsible for the construction of the Solomon link, and was confirmed by its noncatenane self‐assemblies obtained with other similar ruthenium(II) acceptors.     

Pictet–Spengler Synthesis of Quinoline‐Fused Porphyrins and Phenanthroline‐Fused Diporphyrins

Doubly and quadruply quinoline‐fused porphyrins were effectively synthesized through a reaction sequence consisting of Suzuki–Miyaura coupling of β‐borylated porphyrins with 2‐iodoaniline and subsequent Pictet–Spengler cyclization. These quinoline‐fused porphyrins display red‐shifted absorption bands and higher electron‐accepting abilities. This synthetic protocol also allowed the synthesis of phenanthroline‐fused porphyrin dimers, which bound either a Ni^II or Zn^II cation. The resultant metal complexes displayed further red shifted absorption spectra and molecular twists to effect an almost perpendicular arrangement of the two porphyrins.     

Template–Framework Interactions in Tetraethylammonium‐Directed Zeolite Synthesis

Zeolites, having widespread applications in chemical industries, are often synthesized using organic templates. These can be cost‐prohibitive, motivating investigations into their role in promoting crystallization. Herein, the relationship between framework structure, chemical composition, synthesis conditions and the conformation of the occluded, economical template tetraethylammonium (TEA⁺) has been systematically examined by experimental and computational means. The results show two distinct regimes of occluded conformer tendencies: 1) In frameworks with a large stabilization energy difference, only a single conformer was found (BEA, LTA and MFI). 2) In the frameworks with small stabilization energy differences (AEI, AFI, CHA and MOR), less than the interconversion of TEA⁺ in solution, a heteroatom‐dependent (Al, B, Co, Mn, Ti, Zn) distribution of conformers was observed. These findings demonstrate that host–guest chemistry principles, including electrostatic interactions and coordination chemistry, are as important as ideal pore‐filling.     

Solvent‐Free Ball‐Milling Subcomponent Synthesis of Metallosupramolecular Complexes

Subcomponent self‐assembly from components A , B , C , D , and Fe²⁺ under solvent‐free conditions by self‐sorting leads to the construction of three structurally different metallosupramolecular iron(II) complexes. Under carefully selected ball‐milling conditions, tetranuclear [Fe₄( AD ₂)₆]^4? 22‐component cage 1 , dinuclear [Fe₂( BD ₂)₃]^2? 11‐component helicate 2 , and 5‐component mononuclear [Fe( CD ₃)]²⁺ complex 3 were prepared simultaneously in a one‐pot reaction from 38 components. Through subcomponent substitution reaction by adding subcomponent B , the [Fe₄( AD ₂)₆]^4? cage converts quantitatively to the [Fe₂( BD ₂)₃]^2? helicate, which, in turn, upon addition of subcomponent C , transforms to [Fe( CD ₃)]²⁺, following the hierarchical preference based on the thermodynamic stability of the complexes.     

N‐Fusion Approach in Construction of Contracted Carbaporphyrinoids: Formation of N‐Fused Telluraporphyrin

Insertion of PCl₃ into 5,10,15,20‐tetraaryl‐21‐telluraporphyrin leads to a phosphorus complex of N‐fused dihydrotelluraporphyrin with an inverted tellurophene ring. Its CNN coordination core places the macrocycle in the family of contracted carbaporphyrinoids. A cycle of direct transformations affords an elegant triangle of three mutually convertible N‐fused porphyrinoids, with distinct spectroscopic features: antiaromatic, nonaromatic and aromatic. The nonaromatic species has a dome shaped skeleton which forms in the solid state a ball and socket structure with C₆₀.     

Synthesis of Triply Fused Porphyrin‐Nanographene Conjugates

Two unprecedented porphyrin fused nanographene molecules, 1 and 2 , have been synthesized by the Scholl reaction from tailor‐made precursors based on benzo[m]tetraphene‐substituted porphyrins. The chemical structures were validated by a combination of high‐resolution matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (HR MALDI‐TOF MS), IR and Raman spectroscopy, and scanning tunnelling microscopy (STM). The UV‐vis‐near infrared absorption spectroscopy of 1 and 2 demonstrated broad and largely red‐shifted absorption spectra extending up to 1000 and 1400 nm, respectively, marking the significant extension of the π‐conjugated systems.     

When Self‐Assembly Fails: Stepwise Metal‐Directed Synthesis of [2]Catenanes

On the attempted synthesis of a series of homo‐ and heterotrimetallic [2]catenanes by the self‐assembly of a 2‐(pyridin‐4‐ylmethyl)‐2,7‐diazapyrenium ligand, (ethylenediamine)palladium(II) or platinum(II) nitrate, and a dioxoaryl bis(N‐monoalkyl‐4,4′‐bipyridinium) salt as building blocks, both the one‐pot direct self‐assembly of the components and the so called “magic ring” approach fail to produce the expected trinuclear [2]catenanes under thermodynamically driven conditions. However, one of the target supramolecules is obtained by following a stepwise protocol, consisting of the threading of a dinuclear Pt^II metallacycle and the dioxoaryl bis(N‐monoalkyl‐4,4′‐bipyridinium) axle, followed by kinetically controlled Pt^II‐directed cyclization of the corresponding pseudorotaxane.     

Contractile and Extensible Molecular Figures‐of‐Eight

Two large rings, 66‐ (m‐66 ) and 78‐membered ( m‐78 ) rings, each one incorporating two pairs of transition‐metal‐complexing units, have been prepared. The coordinating fragments are alternating bi‐ and tridentate chelating groups, namely, 2,9‐diphenyl‐1,10‐phenanthroline (dpp) and 2,2′,2′,6′′‐terpyridine (terpy) respectively. Both macrocycles form molecular figures‐of‐eight in the presence of Fe^II, affording a classical bis‐terpy complex as the central core. The larger m‐78 ring can accommodate a four‐coordinate Cu^I center with the formation of a {Cu(dpp)₂}⁺ central complex and a highly twisted figure‐of‐eight backbone, whereas m‐66 is too small to coordinate Cu^I. Macrocycle m‐78 thus affords stable complexes with both Fe^II and Cu^I; the ligand around the metal changes from (terpy)₂ to (dpp)₂. This bimodal coordination situation allows for a large amplitude rearrangement of the organic backbone. When coordinated to preferentially octahedrally coordinated Fe^II or Cu^II, the height of the molecule along the coordinating axis of the tridentate terpy ligands is only about 11 Å, whereas the height of the molecule along the same vertical axis is several times as large for the tetrahedral Cu^I complex. Chemically or electrochemically driven contraction and extension motions along a defined axis make this figure‐of‐eight particularly promising as a new class of molecular machine prototype for use as a constitutive element in muscle‐like dynamic systems.     

Anion‐ and Spacer‐Directed Host–Guest Complexes of Bipyridine with Pyrogallol[4]arene

New oval‐shaped capsular and bilayer‐type hydrogen‐bonded arrangements of C‐propyl‐ol‐pyrogallol[4]arene (PgC3‐OH) with bipyridine‐type spacer complexes are reported here. These complexes are engineered by virtue of derivatization of C‐alkyl tails of pyrogallol[4]arene and the use of divergent spacer ligands. Complexes of PgC3‐OH, PgC3‐OH with bpy (4,4′‐bipyridine) and PgC3‐OH with bpa (1,2‐bis(4‐pyridyl)acetylene) have bilayer type arrangements; however, the use of hydrogen chloride causes protonation of bpy molecule, which is then entrapped flat within an offset oval‐shaped dimeric hydrogen‐bonded PgC3‐OH nanocapsule. The presence of chloride anion in the crystal lattice controls the geometry of the resultant nanoassembly.     

Formation and Dynamic Behavior of Mono‐ and Bimetallic Cadmium(II) Porphyrin Complexes: Allosteric Control of Coupled Intraligand Metal Migrations

The complexation behavior of a bis‐strapped porphyrin ligand ( 1 ) towards Cd^II has been investigated by ¹H and ¹¹³Cd NMR spectroscopy with the help of X‐ray diffraction structures. The presence of an overhanging carboxylic acid group on each side of the macrocycle is responsible for the instantaneous insertion of the metal ion(s) at room temperature, and allows the formation of bimetallic species with unusual coordination modes at the origin of unique dynamic behaviors. In the absence of base, a C₂‐symmetric bimetallic complex ( 1Cd₂ ) is readily formed, in which the porphyrin acts as a bridging ligand. Both Cd^II ions are bound to the N core and to a COO^? group of a strap. In contrast, the presence of a base induces a two‐step binding process with the successive formation of mono and bimetallic species ( 1^Cd and 1_Cd?CdOAc ). Formally, a Cd^II ion is first inserted into the N core and experiences a strong out‐of‐plane (OOP) displacement due to the binding of an overhanging carbonyl group in an apical position. A second Cd^II ion then binds exclusively to the strap on the opposite side, in a so‐called hanging‐atop (HAT) coordination mode. These two complexes display a fluxional behavior that relies on intraligand migration processes of the metal ion(s). In 1^Cd , the Cd^II ion exchanges between the two equivalent overhanging apical ligands by funneling through the porphyrin ring. In 1_Cd?CdOAc , the two Cd^II ions exchange their coordination mode (HAT?OOP) in a concerted way while staying on their respective side of the macrocycle, in a so‐called Newton’s cradle‐like motion. The intramolecular pathway was notably evidenced by variable temperature ¹¹³Cd heteronuclear NMR experiments. This coupled motion of the Cd^II cations is under allosteric control; the addition of an acetate anion (the allosteric effector) to the “resting” C₂‐symmetric complex 1Cd₂ affords the dissymmetric complex 1_Cd?CdOAc and triggers equilibrium between its two degenerate states. The rate of the swinging motion further depends on the concentration of AcO^?, with a higher concentration leading to a slower motion. As compared with the related Pb^II and Bi^III bimetallic complexes, the Newton’s cradle‐like motion proceeds faster with the smaller Cd^II ion. These results open the way to novel multistable devices and switches.     

Hierarchical Co‐Assembly Enhanced Direct Ink Writing

Integrating intelligent molecular systems into 3D printing materials and transforming their molecular functions to the macroscale with controlled superstructures will unleash great potential for the development of smart materials. Compared to macromolecular 3D printing materials, self‐assembled small‐molecule‐based 3D printing materials are very rare owing to the difficulties of facilitating 3D printability as well as preserving their molecular functions macroscopically. Herein, we report a general approach for the integration of functional small molecules into 3D printing materials for direct ink writing through the introduction of a supramolecular template. A variety of inorganic and organic small‐molecule‐based inks were 3D‐printed, and their superstructures were refined by post‐printing hierarchical co‐assembly. Through spatial and temporal control of individual molecular events from the nano‐ to the macroscale, fine‐tuned macroscale features were successfully installed in the monoliths.     

Large‐Scale Synthesis of Enantiopure Molecular Cages: Chiroptical and Recognition Properties

A convenient and efficient gram‐scale synthesis for enantiopure hemicryptophane–tren (tren=tris(2‐aminoethyl)amine) derivatives has been developed. The four‐step synthesis is based on the optical resolution of a key intermediate, cyclotriveratrylene, for which the energy barrier for racemization has been measured to ensure that no racemization occurs during the two last steps of the synthetic pathway. The assignments of the absolute configurations have been performed by electronic circular dichroism and the enantiopurity was determined by NMR spectroscopy in the presence of enantiopure camphor sulfonic acid. To highlight the interest of such compounds, the recognition of norephedrine neurotransmitter was investigated and showed a remarkable enantioselectivity towards the C₃ symmetrical hosts. Finally, this highly modular synthetic pathway was used to provide eight enantiopure hemicryptophanes with different sizes, shapes, and functionalities. These results underline the high potential of this approach, which could lead to many applications in chiral recognition or asymmetric supramolecular catalysis.