Rhenium–Pyrazolyl-Based Figure-Eight- and Z‑Shaped Metallocycles: Self-Assembly, Solid-State Structures, Dynamic Properties in Solution, and Competitive Ligand-Induced Supramolecular Transformations into Rhenium-Pyridyl/-Benzimidazolyl/-Phosphine-Based Metallocycles/Acyclic Complexes

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.