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Circular Heterochiral Titanium-Based Self-Assembled Architectures.
Mobian, Pierre; Pham, David-Jérôme; Chaumont, Alain; Barloy, Laurent; Khalil, Georges; Kyritsakas, Nathalie.
Afiliação
  • Mobian P; Université de Strasbourg, CNRS, CMC UMR 7140 (team SFAM), F-67000 Strasbourg, France.
  • Pham DJ; Université de Strasbourg, CNRS, CMC UMR 7140 (team SFAM), F-67000 Strasbourg, France.
  • Chaumont A; Université de Strasbourg, CNRS, CMC UMR 7140 (team MSM), F-67000 Strasbourg, France.
  • Barloy L; Université de Strasbourg, CNRS, CMC UMR 7140 (team SFAM), F-67000 Strasbourg, France.
  • Khalil G; Université de Strasbourg, CNRS, CMC UMR 7140 (team SFAM), F-67000 Strasbourg, France.
  • Kyritsakas N; Université de Strasbourg, CNRS, CMC UMR 7140 (team LTM), F-67000 Strasbourg, France.
J Am Chem Soc ; 146(20): 14067-14078, 2024 May 22.
Article em En | MEDLINE | ID: mdl-38728688
ABSTRACT
Circular trinuclear helicates have been synthesized from a bis-biphenol strand (LH4), titanium isopropoxide, and various diimine ligands. These self-assembled architectures constructed around three TiO4N2 nodes have a heterochiral structure (C1 symmetry) when 2,2'-bipyridine (A), 4,4'-dimethyl-2,2'-bipyridine (B), 4,4'-bromo-2,2'-bipyridine (C), or 4,4'-dimethyl-2,2'-bipyrimidine (D) is employed. Within these complexes, one nitrogen ligand is endo-positioned inside the metallo-macrocycle, whereas the other two diimine ligands point outside the helicate framework. This investigation highlights that the nitrogen ligand which does not participate in the helicate framework of the complex controls the overall symmetry of the helicate since the 2,2'-bipyrimidine chelate (F) ends in the formation of a homochiral aggregate (C3 symmetry). The lack of symmetry found in the solid state for the trinuclear species ([Ti3L3(B)3], [Ti3L3(C)3], and [Ti3L3(D)3]) is observed for these complexes in solution (dichloromethane or chloroform). Remarkably, the 2,2'-bipyrazine ligand (ligand E) ends in the formation of a hexameric aggregate formulated as [Ti6L6(E)6], whereas the use of 4,4'-dimethyl-2,2'-bipyrimidine (ligand D) permits to generate the dinuclear complexes ([Ti2L(D)2(OiPr)4] and [Ti2L2(D)2]) in addition to the trimeric structure [Ti3L3(D)3]. The behavior of [Ti3L3(A)3] in solution, on the other hand, is unique since an equilibrium between the homochiral and the heterochiral form is reached within 17 days after the complex has been dissolved in dichloromethane (C3-[Ti3L3(A)3]/C1-[Ti3L3(A)3] ratio = 0.3). In chloroform, the heterochiral form of [Ti3L3(A)3] is stable for the same period of time, evidencing the dependence of this stereochemical transformation toward the solvent medium. The thermodynamic and kinetic parameters linked to this stereochemical equilibrium have been obtained and point to the fact that the transformation is intramolecular and not induced by the presence of external ligands. The thermodynamic constant of the C1-[Ti3L3(A)3]/C3-[Ti3L3(A)3] equilibrium is found to be K = 0.34 ± 10%. Further evidence to rationalize this solvent-induced symmetry switch is obtained via a DFT calculation and classical molecular dynamics. In particular, this computational investigation elucidates the reason why the stereochemical transformation of a heterochiral architecture into a homochiral structure is possible only for a trinuclear assembly containing ligand A.

Texto completo: 1 Coleções: 01-internacional Base de dados: MEDLINE Idioma: En Revista: J Am Chem Soc Ano de publicação: 2024 Tipo de documento: Article País de afiliação: França

Texto completo: 1 Coleções: 01-internacional Base de dados: MEDLINE Idioma: En Revista: J Am Chem Soc Ano de publicação: 2024 Tipo de documento: Article País de afiliação: França