Rhenium-Pyrazolyl-Based Figure-Eight- and Z-Shaped Metallocycles: Self-Assembly, Solid-State Structures, Dynamic...

Rhenium(I)tricarbonyl core-based heteroleptic "figure-eight"- and Z-shaped metallocycles (1a-4a) of the general formula fac-[{(CO)₃Re(μ-L)Re(CO)₃}₂(dppz)₂] were self-assembled from Re₂(CO)₁₀, H₂-L (H₂-L = 5,8-dihydroxy-1,4-naphthaquinone (H₂-dhnq) for 1a; 1,4-dihydroxy-9,10-anthraquinone (H₂-dhaq) for 2a; 6,11-dihydroxy-5,12-naphthacenedione (H₂-dhnd) for 3a; 2,2'-bisbenzimidazole (H₂-bbim) for 4a), and bis(4-((pyrazolyl)methyl)phenylmethane) (dppz) via one-pot coordination-driven synthetic approach. The molecular structures of 1a and 4a were unambiguously confirmed by single-crystal X-ray diffraction (SC-XRD) methods. The metallocycles in the DMSO solution exist as an acyclic dinuclear-DMSO adduct of the general formula fac-[{(CO)₃Re(μ-L)Re(CO)₃}(DMSO)₂] (1b, L = dhnq; 2b, L = dhaq; 3b, L = dhnd; 4b, L = bbim) and dppz, which are in dynamic equilibrium. The dynamic behavior of the rhenium-pyrazolyl bond in the solution state was effectively utilized to transform metallocycles 1a-4a into pyridyl/benzimidazolyl/phosphine donor-based heteroleptic metallocycles and acyclic dinuclear complexes (4-13). These include tetranuclear rectangles fac-[{(CO)₃Re(μ-L)Re(CO)₃}₂(4,4'-bpy)₂] (4 and 11, L = dhaq for 4 and bbim for 11), dinuclear metallocycles fac-[{(CO)₃Re(μ-L)Re(CO)₃}(dpbim)] (5-7 and 12; L = dhnq for 5, dhaq for 6, dhnd for 7, and bbim for 12), and dinuclear acyclic complexes fac-[{(CO)₃Re(μ-L)Re(CO)₃}(PTA)₂] (8-10 and 13; L = dhnq for 8, dhaq for 9, dhnd for 10, and bbim for 13). These transformations were achieved through component-induced supramolecular reactions while treating with competitive ligands 4,4'-bipyridine (4,4'-bpy), bis(4-((1H-benzoimidazole-1-yl)methyl)phenyl)methane (dpbim), and 1,3,5-triaza-7-phosphaadamantane (PTA). The reaction mixture in the solution was analyzed using NMR and electrospray ionization mass spectrometry (ESI-MS) analysis. Additionally, crystal structures of 4, 6, and 13, which were obtained in the mixture of the solutions, were determined, providing unequivocal evidence for the occurrence of supramolecular transformation within the system. The results reveal that the size of the chelating ligand and the pyrazolyl donor angle of the ditopic ligand play crucial roles in determining the resulting solid-state metallacyclic architecture in these synthetic combinations. The dynamic behavior of the rhenium-pyrazolyl bond in the metallocycles can be utilized to transform into other metallocycles and acyclic complexes using suitable competing ligands via ligand-induced supramolecular transformations.