Diversity and Complexity through Reversible Multiple Orthogonal Interactions in Multicomponent Assemblies

Shape Complementary Coordination Self-Assembly of a Redox-Active Heteroleptic Complex

We present here the coordination self-assembly of a new heteroleptic (bpyPd)₄L¹L₂² coordination complex (1) from one novel pyridinium-functionalized bis-2,4,6-tris(pyridin-3-yl)-1,3,5-triazine (bis-3-TPT, L¹) macrocyclic ligand, two separate 3-TPT (L²) ligands, and four cis-blocking bpyPd(NO₃)₂ (bpy = 2,2'-bipyridine). While homoleptic self-assemblies with either L¹ or L² gave dynamic mixtures of products, a single thermodynamic heteroleptic complex was obtained driven by the shape complementarity of building blocks. Moreover, the redox-active nature of the heteroleptic assembly facilitates the highly efficient catalytic aerobic photo-oxidation of aromatic secondary alcohols under mild conditions.

Triple Self-Sorting in Constitutional Dynamic Networks: Parallel Generation of Imine-Based CuI , FeII , and ZnII Complexes

Three imine-based metal complexes, having no overlap in terms of their compositions, have been simultaneously generated from the self-sorting of a constitutional dynamic library (CDL) containing three amines, three aldehydes, and three metal salts. The hierarchical ordering of the stability of the three metal complexes assembled and the leveraging of the antagonistic and agonistic relationships existing between the constituents within the constitutional dynamic network corresponding to the CDL were pivotal in achieving the sorting. Examination of the process by NMR spectroscopy showed that the self-sorting of the FeII and ZnII complexes depended on an interplay between the thermodynamic driving forces and a kinetic trap involved in their assembly. These results also exemplify the concept of "simplexity"-the fact that the output of a self-assembling system may be simplified by increasing its initial compositional complexity-as the two complexes could self-sort only in the presence of the third pair of organic components, those of the CuI complex.

Self-sorting of two imine-based metal complexes: balancing kinetics and thermodynamics in constitutional dynamic networks

A major hurdle in the development of complex constitutional dynamic networks (CDNs) is the lack of strategies to simultaneously control the output of two (or more) interconnected dynamic processes over several species, namely reversible covalent imine bond formation and dynamic metal-ligand coordination. We have studied in detail the self-sorting process of 11 constitutional dynamic libraries containing two different amines, aldehydes and metal salts into two imine-based metal complexes, having no overlap in terms of their compositions. This study allowed us to determine the factors influencing the fidelity of this process (concentration, electronic and steric parameters of the organic components, and nature of the metal cations). In all 11 systems, the outcome of the process was primarily determined by the ability of the octahedral metal ion to select its pair of components from the initial pool of components, with the composition of the weaker tetrahedral complex being imposed by the components rejected by the octahedral metal ions. Different octahedral metal ions required different levels of precision in the "assembling instructions" provided by the organic components of the CDN to guide it towards a sorted output. The concentration of the reaction mixture, and the electronic and steric properties of the initial components of the library were all found to influence the lifetime of unwanted metastable intermediates formed during the assembling of the two complexes.

Syntheses, Structures, and Solution Studies of Multicomponent Macrocycles and Cages Based on Versatile Ligands

Different types of multinuclear half-sandwich rhodium macrocycles and cages were designed and synthesized by using two similar multifunctional hydroxamate ligands (pyrazine-2-hydroxamic acid (NaHL¹ ) and 4,4'-bipyridine-2-hydroxamic acid (KHL² )) featuring one monodentate site and two pairs of chelating sites. The Rh^III -Pd^II heterometallic macrocycles were constructed by using the semi-open palladium(II) source [Pd(en)Cl₂ ] with two free acceptor sites. However, only one kind of macrocycle was found when the shorter ligand L¹ was used, while in for the larger ligand, various spectroscopic techniques demonstrated the coexistence of hexanuclear and octanuclear macrocycles in solution and the proportions of both components depended on concentration and temperature. The palladium salt Pd(NO₃ )₂ , as a source of "naked" Pd²⁺ , was introduced to assemble the cuboid-shaped cage composed of two types of metal ions and three types of organic ligands. In addition, two silver(I)-containing mixed-metal complexes bridged by pyrazine were obtained, in which two forms of decanuclear complex with C_2v and C_2h point symmetry cocrystallized-one is a polymeric structure and the other is a discrete cage. However, the third form, with D₂ point symmetry, was found in the larger cage.

Stepwise self-assembly of a discrete molecular honeycomb using a multitopic metallo-organic ligand

A molecular bismetallo-hexagon and a honeycomb fractal have been assembled with multiple tpy-M²⁺-tpy connectivities. The key metallo-organic ligand was created by a reaction on complex strategy.

Controlled Orthogonal Self-Assembly of Heterometal-Decorated Coordination Cages

Multiple orthogonal coordinative interactions were utilized to construct heterometal-decorated tetrahedral cages from in situ formed trinuclear Zr^IV clusters through the combination with other metal ions such as Cu^II or Pd^II . Through effective use of the hard/soft acid/base principle, the orthogonal self-assembly process of Zr-bpydc-CuCl₂ (H₂ bpydc=2,2-bipyridine-5,5-dicarboxylic acid) can be finely controlled using three strategies: post-synthetic metallization, a stepwise metalloligand approach, or a one-pot reaction.

Competition-driven selection in covalent dynamic networks and implementation in organic reactional selectivity

Competition among reagents in dynamic combinatorial libraries of increased complexity leads to reactional self-sorting. This fundamental principle allowed development of selective dynamic protecting groups for controlled sequential derivatization of polyamines.

Competition among reagents in dynamic combinatorial libraries of increased complexity leads to reactional self-sorting (improved regioselectivity) in mixtures of aldehydes and oligoamines. High selectivity of a given library component is transferred to a different reacting component of low selectivity through a network of underlying equilibrating reactions which provide component exchange between all species. The selectivity of various carbonyl compounds in reactions with amines was also assessed towards the formation of defined sequences of residues along oligoamine chains. The approach was further exploited for defining selective dynamic protecting groups (DPGs), based on the reversible linkage between the substrate and the protecting group. They represent an intermediate approach between the conventional protecting groups and the protecting-group-free approach in organic synthesis. Removal of the protecting group is effected via dynamic exchange trapping by formation of a more stable product. The establishment of equilibrium eliminates the need for isolation and purification of the dynamically protected intermediate(s) and enables as well the selective sequential derivatisation of oligoamines. The DPG concept can be generalised to other reversible reactions and can thus represent a valuable alternative in the design of total synthesis of complex molecules.

Shape and size directed self-selection in organic cage formation

The selective formation of a single isomer of a [3+2] self-assembled organic cage from a reaction mixture of an unsymmetrical aldehyde and a flexible amine is discussed. The experimental and theoretical findings suggest that in such a process, the geometric features of the aldehyde play a key role.

Selective Formation of Heterometallic Ru-Ag Supramolecules via Stoichiometric Control of Multiple Different Tectons

Stoichiometric control of Ru, Ag, and tetrazolyl ligands resulted in the formation of different heterometallic Ru-Ag supramolecular architectures. Although the reaction of Ru and 5-(2-hydroxyphenyl)-1H-tetrazolyl (LH2) in a molar ratio of 2:1 or 6:4 resulted in the formation of dimeric or hexameric Ru complexes, Ag metal ions caused the Ru complexes to form three-dimensional cylindrical Ru6Ag6L6 and double-cone-shaped Ru6Ag8L6 complexes by occupying vacant coordination sites.

Metal-coordination-driven mixed ligand binding in supramolecular bisporphyrin tweezers

The mixed ligand polymers of Mg(ii)bisporphyrin with heterogeneous guest pairs have been synthesized just by mixing the host and guests in one pot and structurally characterized. The guest ligands are bound selectively between the inside and the outside of the bisporphyrin cavity.

A seven-component metallosupramolecular quadrilateral with four different orthogonal complexation vertices

The 4-fold completive self-sorting of a ten-component library (7 dissimilar donors and 3 different acceptors) resulted in the clean self-assembly of four dynamic orthogonal complexes that were used as cornerstones in two novel six- and seven-component scalene quadrilaterals.

Merging strong and weak coordination motifs in the integrative self-sorting of a 5-component trapezoid and scalene triangle

In a dynamic six-component library, the formation of the rather weak HETPYP-I complexation can be enforced by exploiting the orthogonality and high stability of its counterpart in the sorting process, a HETTAP complex. The concept was used in a follow-up integrative self-sorting, enabling the formation of two five-component supramolecular structures: a trapezoid and a scalene triangle.

Supramolecular chemistry with ureido-benzoic acids

A novel, complementary quadruple hydrogen-bonding motif is presented that shows very strong dimerization and is switchable with pH.

A series of trifacial Pd6 molecular barrels with porphyrin walls

Three new nanoscopic trigonal prisms, [(tmen)(6) Pd(6) (H(2)L)(3)](NO(3))(12) (1), [(Meen)(6) Pd(6)(H(2) L)(3)](NO(3))(12) (2), and [(2,2'-bipy)(6)Pd(6) (H(2)L)(3)](NO(3))(12) (3), have been synthesized in excellent yields through single-step metal-ligand-coordination-driven self-assembly using 5,10,15,20-tetrakis(3-pyridyl)porphyrin (H(2)L) as a donor and cis-blocked Pd(II) 90° acceptors. These complexes were fully characterized by spectroscopic studies and single-crystal X-ray diffraction. All of these barrels quantitatively bind Zn(II) ions in the N(4) pockets of the porphyrin walls at room temperature. Their corresponding zinc-embedded complexes, [(tmen)(6)Pd(6)(ZnL)(3)](NO(3))(12) (1 a), [(Meen)(6) Pd(6)(ZnL)(3)](NO(3))(12) (2 a), and [(2,2'-bipy)(6)Pd(6)(ZnL)(3)](NO(3))(12) (3 a), were synthesized under ambient conditions by the post-synthetic binding of Zn(II) ions into the H(2)N(4) pockets of the porphyrin walls of these complexes. These zinc-embedded complexes were characterized by electronic absorption, fluorescence emission, (1)H NMR spectroscopy, as well as elemental analysis. Complexes 1-3 exhibited considerable microporosity in their solid state. Complex 1 was an efficient adsorbent for nitrogen gas and EtOH, MeOH, and water vapors.

Coordination-driven self-assembly of ruthenium-based molecular-rectangles: synthesis, characterization, photo-physical and anticancer potency studies

A suite of eight cationic, tetra-metallic molecular rectangles (1-8) was generated via coordination-driven self-assembly using four dicarboxylate-bridged arene-Ru precursors (A1-A4) with one of two dipyridyl ligands (D1, D2). The high-yielding (84-92%) rectangles were characterized by (1)H NMR and HR-ESI-MS to support their structural assignments. The molecular structure of 5 was determined by single crystal X-ray analysis, which indicated that two D2 ligands bridge two A1 acceptors to form a rectangular construct. The photophysical properties of these metalla-rectangles and their molecular precursors were also investigated, as well as an MTT assay to evaluate the in vitro cytotoxicities relative to two chemotherapeutic agents, cisplatin and doxorubicin. MTT assays were conducted using SK-hep-1 (liver cancer) and HCT-15 (colon cancer) human cancer cell lines. Compounds 3, 4, 7 and 8 showed significant activity, with IC(50) values comparable to those of cisplatin and doxorubicin.

A facile approach toward multicomponent supramolecular structures: selective self-assembly via charge separation

A novel approach toward the construction of multicomponent two-dimensional (2-D) and three-dimensional (3-D) metallosupramolecules is reported. Simply by mixing carboxylate and pyridyl ligands with cis-Pt(PEt(3))(2)(OTf)(2) in a proper ratio, coordination-driven self-assembly occurs, allowing for the selective generation of discrete multicomponent structures via charge separation on the metal centers. Using this method, a variety of 2-D rectangles and 3-D prisms were prepared under mild conditions. Moreover, multicomponent self-assembly can also be achieved by supramolecule-to-supramolecule transformations. The products were characterized by (31)P and (1)H multinuclear NMR spectroscopy, electrospray ionization mass spectrometry, and pulsed-field-gradient spin echo NMR techniques together with computational simulations.

From an eight-component self-sorting algorithm to a trisheterometallic scalene triangle

Using motifs from 3-fold completive self-sorting in an eight-component library, we report on the design and fabrication of a fully dynamic trisheterometallic scalene triangle, a demanding supramolecular structure that complements the so far known triangular structures.

Combining dynamic heteroleptic complex formation with constitutional dynamic synthesis: a facile way to M3LL' cage assemblies

The quantitative preparation of heteroleptic copper(I) complexes arising from a combination of 2,9-diarylphenanthrolines and iminopyridines (Schiff bases) is described. This strategy was applied to construct mono- and binuclear complexes but equally a discrete three-dimensional M(3)LL' cage. By means of a constitutional dynamic synthesis, the heteroleptic aggregates were equally prepared from four-component mixtures using the copper(I) center as a catalyst for the in situ generation of the iminopyridine ligands.