Study of the different behaviour of thiazolin and thiazin indazole derivatives with palladium(II) acetate

The study of the reactivity of the ligands 2-(indazol-1-yl)-2-thiazoline (1) and 2-(indazol-1-yl)-1,3-thiazine (2) with palladium(II) acetate has allowed the isolation of different compounds. For the thiazolin indazole derivative (1) a cyclopalladated compound: (μ-OAc)2[Pd(k2-C,N-TnInA)]2 (1a) with a bidentate [C(sp2,phenyl),N]− ligand and a central “Pd(μ-OAc)2Pd” unit was obtained. Treatment of the dimeric compound 1a with sodium acetylacetonate produced the mononuclear compound [Pd(k2-O,O′-acac)(k2-C,N-TnInA)] (1c). The reaction of 1a with LiCl followed by the addition of PPh3 gave the compound [PdCl(PPh3)(k2-C,N-TnInA)] (1e) where the acetate groups were replaced by Cl− and PPh3 ligands, and with the PPh3 in a cis-arrangement to the metallated carbon atom. The solid-state structure of 1e was determined by single-crystal X-ray diffraction methods. The reaction of 2 with palladium(II) acetate produced, in contrast to ligand 1, the complex cis-[Pd(OAc)2(k2-N,N′-TzIn)] (2a) with a bidentate [N,N′] ligand. Compound 2a reacted with LiCl giving cis-[PdCl2(k2-N,N′-TzIn)] (2b), where the acetate groups were exchanged by chloride ligands. DFT calculations suggest that the most favoured compound obtained from the reaction between 1 and palladium(II) acetate should be the cyclopalladated one, while for 2 the formation of the [N,N′] coordinated complex is less unfavoured.

Graphical abstractThe study of the reactivity of the ligands 2-(indazol-1-yl)-2-thiazoline or 2-(indazol-1-yl)-1,3-thiazine with palladium(II) acetate has allowed the isolation of distinct compounds. DFT calculations suggest that the most favoured isomer obtained should be the cyclopalladated one, but for 2-(indazol-1-yl)-1,3-thiazine the formation of the [N,N′] coordinated isomer is less unfavoured.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Reaction of palladium(II) acetate with ligands thiazoline and thiazine indazole derivatives. ► Synthesis of a new six-membered ring cyclopalladate compound with a ligand thiazolin indazole derivative. ► Determination of the crystal structure of compound [PdCl(PPh3)(k2-C,N-TnInA)] by X-ray diffraction. ► The thiazine indazole derivative acts as a [N,N′] group in the coordination complex obtained. ► DFT calculations suggest the different behaviour for the two similar ligands.