A Rigidity-Modulated Approach toward the Construction of Metallacycles from a Flexible Tetratopic Ligand

Abstract

Conformation control of a flexible tetratopic ligand by modulation of the length of the rigid bridging ligand is achieved during the self-assembly of metallacycles. The ability to control the conformation of the flexible ligand using an ancillary rigid ligand provides a new method for the preparation of novel metallacycles that contain both flexible and rigid modules with highly accurate prediction of the final structures.Precise control of supramolecular metallacycles requires a rational design of molecular components, because the information that determines the specific assembly should be encoded in the molelcular architecture. 1 Recently, the use of flexible motifs to construct metallacycles has increased because of the advantages associated with their use, such as adaptive recognition properties and breathing ability in the solid state. [2][3][4][5] Flexible organic components are generally less predictable during self-assembly and have a tendency to generate [2]catenanes 2 or oligomers upon reaction with metal ions. Prior research in this area has focused on the use of di-and tritopic flexible N-donors to construct both ionic and neutral metallacycles. [2][3][4][5][6] The synthesis and use of semirigid tetratopic N-donors as structural components for metallacycles is rare because of their higher conformational flexibility, which must be restricted to obtain well-preorganized subunits. 7 Herein, we report an effective rigiditymodulated approach for the design of neutral metallacycles. The rigid anionic linker responsible for determination of M 3 3 3 M separation allows for conformational control of the flexible motif with simultaneous use of a rigid bis(chelator), tetratopic flexible N-donors, and fac-Re(CO) 3 cores during self-assembly (Scheme 1).In this study, the flexible ligand 1,2,4,5-tetrakis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene (TXyBim) and two rigid moieties, 2,2 0 -bis(benzimidazolyl) (H 2 -Bim) 8 and chloranilic acid (H 2 -CA), were explored as basic building units. In the case of TXyBim, four benzimidazoles are connected via flexible methylene groups to an arene core. This flexibility permits TXyBim to adopt several possible conformations because of the orientation of the four benzimidazolyl arms (Chart S1 in the Supporting Information). 9 Compound 1 was assembled from Re 2 (CO) 10 , TXyBim, and H 2 -Bim in toluene in 68% yield under solvothermal conditions (Scheme 2). 10 The resulting yellow product is airand moisture-stable and slightly soluble in polar solvents. The IR spectrum of 1 exhibited strong bands at 2018, 1914, and 1900 cm -1 , characteristic of fac-Re(CO) 3 . The structure of compound 1 was determined by X-ray crystallographic analysis, which revealed that metallacycle 1 contains four fac-Re(CO) 3 cores, two Bim groups, and one TXyBim moiety, as shown in Figure 1. 10 The coordination geometry around the Re centers is a distorted octahedron with a C 3 N 3donor environment. The dianionic Bim is coordinated in a

One-Step Orthogonal-Bonding Approach to the Self-Assembly of Neutral Rhenium-Based Metallacycles: Synthesis, Structures, Photophysics, and Sensing Applications

“…Compounds 24 and 25 were assembled by reacting a mixture of Re 2 (CO) 10 , TXyBim, and H 2 Bim or H 2 CA in toluene under solvothermal conditions in a one-step process (Scheme 12). 43 The coordination geometry around the Re centers in 24 and 25 is described as a distorted octahedral shape with a C 3 N 3 -, and C 3 NO 2 -donor environment, respectively, as evidenced by solid-state structures (Figure 10). The Re 3 3 3 Re distance in 25 is 8.141 Å, representing ∼2.9 Å longer than that found in 24.…”

“…In another contribution from our laboratory, we reported that the rigid anionic linker responsible for determination of M···M separation allows for conformational control of the flexible motif with the simultaneous use of a short or long rigid bis(chelator), tetratopic flexible N-donors (1,2,4,5-tetrakis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene, TXyBim), and fac -Re(CO) 3 cores during self-assembly (Scheme ). Compounds 24 and 25 were assembled by reacting a mixture of Re 2 (CO) 10 , TXyBim, and H 2 Bim or H 2 CA in toluene under solvothermal conditions in a one-step process (Scheme ) …”

New Class of Phosphine Oxide Donor-Based Supramolecular Coordination Complexes from an in Situ Phosphine Oxidation Reaction or Phosphine Oxide Ligands

“…Complex 3 was air- and moisture-stable and sparingly soluble in polar organic solvents. Related N-donor-based SCC [(Re(CO) 3 ) 4 (CA) 2 (1,2,4,5-tetrakis(5,6-dimethylbenzimidazol-1-methyl)benzene)] is insoluble . The FT-IR spectrum of 3 confirms the presence of fac -Re(CO) 3 , CA 2– , PO, and P–OMe units.…”

Neutral discrete metal–organic cyclic architectures: Opportunities for structural features and properties in confined spaces

“…During the self-assembly process, the rigid anionic linker, which is responsible for determining M· · ·M separation, allows for conformational control of the flexible supramolecular entities [270]. The reaction of two different length rigid moieties such as 2,2 -bis(benzimidazolyl) (L52) and chloranilic acid (L133), with flexible ligand 1,2,4,5-tetrakis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene (H 2 L137, TXyBim) and Re 2 (CO) 10 A single-crystal X-ray diffraction analysis showed that compounds 164 and 165 adopted a tetrametallic metallacyclic structure, in which the Re centers had a distorted octahedron with Scheme 65.…”

“…The reaction of two different length rigid moieties such as 2,2 -bis(benzimidazolyl) (L52) and chloranilic acid (L133), with flexible ligand 1,2,4,5-tetrakis(5,6-dimethylbenzimidazol-1-ylmethyl)benzene (H 2 L137, TXyBim) and Re 2 (CO) 10 A single-crystal X-ray diffraction analysis showed that compounds 164 and 165 adopted a tetrametallic metallacyclic structure, in which the Re centers had a distorted octahedron with Scheme 65. Self-assembly of metallacycles via conformational selection from various conformers [270]. a C 3 N 3 -and C 3 NO 2 -donor environment, respectively (Fig.…”