Competitive Transmetalation of First-Row Transition-Metal Ions between Trinuclear Triple-Stranded Side-by-Side Helicates

Unexpected linkage isomerism in chiral tetranuclear bis-tridentate (1,2,3-triazol-4-yl)-picolinamide (tzpa) grids

The synthesis of a chiral bis-tridentate (1,2,3-triazol-4-yl)-picolinamide (tzpa) ligand is described and its coordination chemistry with Cu(NO3)2 and [Cu(MeCN)4]PF6 is explored in the crystalline phase as well as in solution. Chiral [2 × 2] tetranuclear square grid complexes [Cu4(H21)4](NO3)8 and [Cu4(H1)4](PF6)4 were observed, and crystallographically analysed, these being linkage isomers with N4O2 and N5O coordination spheres, respectively. These come about by an unusual in situ amide deprotonation and coordination, which accompanies a CuI → CuII oxidation process.

Diastereoselective Control of Tetraphenylethene Reactivity by Metal Template Self-Assembly

The reaction of 4,4',4'',4'''-(ethene-1,1,2,2-tetrayl)tetraaniline with 2-pyridinecarboxaldehyde and iron(II) chloride resulted, after aqueous workup, in the diastereoselective formation of an [Fe₂ L₃ ]⁴⁺ triple-stranded helicate structure, irrespective of the stoichiometry employed. The helicate structure was characterized in solution by multinuclear NMR spectroscopy, and in the solid state by single-crystal X-ray crystallography. The reaction of iron(II) tetrafluoroborate or iron(II) bistriflimide with the tetraaniline and 2-pyridinecarboxaldehyde allowed the formation of an [Fe₈ L₆ ]¹⁶⁺ cube when the appropriate stoichiometry was used, but these structures were unstable with respect to hydrolysis. The pendant amine groups on the helicate can be functionalized by reaction with acid chlorides or anhydrides, and the resulting functionalized tetraphenylethene (TPE) units were isolated by the reaction of the helicate with tris(2-aminoethyl)amine. The emission properties of the TPE units were studied in THF/water mixtures, and they were found by dynamic light scattering to self-assemble into large (av. diameter 250 nm) structures.

Dihydrogen phosphate-containing dinuclear double assemblies that demonstrate phosphate reactivity to the tetrafluoroborate anion

The ligands L1 and L2 both form dinuclear assemblies with Cu(ii) and these react with dihydrogen phosphate so that the anion is incorporated within the assembly (e.g. [Cu2L2(H2PO4)]3+). However, in the presence of tetrafluoroborate anions the phosphate undergoes reaction with the anion forming [Cu3(L1)3(O3POBF3)]3+ and [Cu2(L2)2(O2P(OBF3)2)]+.

Transmetalation for Flexible Pendant-Armed Schiff-Base Macrocyclic Complexes Influenced by Halide Effects

Three 46-membered [2 + 2] pendant-armed Schiff-base macrocyclic dinuclear Cd^II and Cu^II complexes (2a, 2b, and 3b) and one 23-membered [1 + 1] Cu^II macrocycle 4a were prepared from the template-directed condensation reactions between 1,2-bis(2-aminoethoxy)-ethane and extended Cl-dialdehyde in the presence of CdX₂ and CuX₂ (X = Cl and Br), in which halide effects play important roles in the organization of final macrocyclic complexes in addition to the dominant influence of metal cations. Transmetalation was intensively studied among these Cd^II and Cu^II complexes with large and flexible macrocyclic ligands, including two previously synthesized dinuclear Zn^II macrocycles (1a and 1b). Our results indicate that Zn^II → Cu^II and Cd^II → Cu^II transmetalation proceeds more quickly than that from Cd^II to Zn^II, and all the processes are found to be irreversible. It is noted that a [2 + 2] heterodinuclear Cd^IIZn^II macrocyclic intermediate could be detected by ESI-MS together with [2 + 2] homodinuclear Cd^II and Zn^II macrocyclic complexes. Furthermore, distinct halide behavior was observed in the in situ Cd^II → Cu^II and Zn^II → Cu^II metal-ion exchange. That is to say, [2 + 2] macrocycles (1a and 2a) could be converted to [1 + 1] macrocycles 4a and 4b under the reflux condition in the case of CuCl₂, accompanied by the configurational transformation from half-folded dinuclear Zn^II and Cd^II to unfolded Cu^II macrocyclic skeleton. In contrast, CuBr₂ leads to a highly efficient transmetalation to corresponding [2 + 2] dinuclear Cu^II complex 3b from both 1b and 2b no matter the experimental condition used.

Anion-dependent thermo-responsive supramolecular superstructures of Cu(ii) macrocycles

A heteroditopic ligand predominantly self-assembled into a dinuclear Cu(ii) macrocycle with various Cu²⁺ salts. However, each macrocycle is further hierarchically assembled to distinct supramolecular superstructures, where the shape of the morphology is found to be highly dependent on the counter-anions and temperature.