Self-assembly of thiolato-bridged ester-functionalized Re(i)-based tetranuclear spiro-metallacyclophanes

Abstract

Rhenium tricarbonyl core-based thiolato-bridged spiro-metallacyclic tetranuclear compounds of general formula [{(CO)₃Re(μ-SR)₂Re(CO)₃}₂(μ-η⁴-ptpc)] (1–3) (R = phenyl (1), p-tolyl (2), and benzyl (3)) were accomplished by the reaction of rudimentary Re₂(CO)₁₀, diaryl disulfides, and a flexible tetradentate ligand, pentaerythritol tetrakis pyridine carboxylate (ptpc), under solvothermal reaction conditions. Oxidative addition of diaryl disulfide (RS–SR) across the Re–Re bond of the dirhenium decacarbonyl with the simultaneous coordination of the pyridyl moiety of the ptpc ligand resulted in the formation of tetranuclear spiro-metallacyclophanes in a single step. Compounds 1–3 were characterized using UV-Vis, IR and NMR spectroscopic techniques, elemental analysis, and ESI-Mass spectrometry. Single-crystal X-ray crystallographic studies of 3 ascertained the spirocyclic structure of the metallacyclophane. Furthermore, the bent spirocyclic structural features of 3 were rationalized theoretically using DFT calculations. The molecular recognition capabilities of spiro-metallacyclic hosts 2 and 3 with functionalized aromatic guests p-phenylenediamine and benzene-1,4-diol were investigated using UV-Vis absorption and emission spectrophotometric methods. Additionally, in silico molecular docking studies for compound 3 with KasA protein were performed.