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Synthesis and Characterization of a Thiopyridazinylmethane-Based Scorpionate Ligand: Formation of Zinc Complexes and Rearrangement Reaction

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posted on 19.09.2017, 19:53 by Michael Tüchler, Stefan Holler, Elke Huber, Susanne Fischer, A. Daniel Boese, Ferdinand Belaj, Nadia C. Mösch-Zanetti
The ligand tris­(6-tert-butyl-3-thiopyridazinyl)­methane ([Tntm]­H) was synthesized by the reaction of 6-tert-butyl-3-thiopyridazine with bromoform and reacted with zinc bis­(trimethylsilylamide) (Zn­(N­{SiMe3}2)2) to form [Tntm]­Zn­(N­{SiMe3}2) (1). This complex further reacts with protic and acidic substrates, generating the zinc thiolate complex [Tntm]­Zn­(StBu) (2) and zinc benzoate complex [Tntm]­Zn­(O2C-Me2C6H3) (3a). In all compounds [Tntm] was found to have tridentate coordination to the metal center in a κ3-C,N,N fashion, as established by single-crystal X-ray diffraction analyses. In solution, rapid dynamic κ34 equilibrium occurs at room temperature, while 1H NMR spectroscopy at −30 °C confirms the asymmetric solid-state structure. Furthermore, complex 3a shows a rearrangement reaction in solution where the ligand isomerizes to give a κ4-C,N,N,S (3b) and a κ4-C,N,S,S isomer (3c), respectively. Density functional theory (DFT) calculations reveal 3b and 3c to be 13.7 and 15.6 kJ/mol more stable in methylene chloride than 3a, respectively. All compounds were fully characterized via 1H, 13C, and variable temperature NMR spectroscopy, as well as elemental and single-crystal X-ray diffraction analysis.