Synthesis and Photochemical Study of Thiazolidine Derivatives of Cymantrene and the Corresponding Dicarbonyl Chelates.

Isomeric 4,5‐dihydro‐2‐[(cymantrenylmethyl)thio]thiazole (1) and 3‐(cymantrenylmethyl)‐1,3‐thioazolidine‐2‐thione (2) were synthesized and photochemical behavior and spectral characteristics of tricarbonyl and dicarbonyl complexes were studied. Irradiation of compounds 1 and 2 results in the formation of stable chelates due to coordination of manganese to the donor nitrogen and sulfur atoms of the thiazolidine substituent. Photolysis is accompanied with a colour change and the corresponding changes in the UV/Vis spectra depending on the solvent used. In the presence of CO, the dicarbonyl chelates enter the dark reaction to give the parent tricarbonyl complexes thus forming intermolecular photochromic systems. Photolysis of the dicarbonyl chelate 5 gives the isomeric chelate 6, which in the course of the dark isomerization transforms into complex 5. Chelates 5 and 6 form an intramolecular photochromic pair. An intramolecular photochromic pair including N‐ and S‐coordinated chelates of thiazolidine derivatives of cymantrene is for the first time reported. The reverse reaction occurs via SN1 mechanism with a half‐conversion time for the dark isomerization being 160 min. The quantum yield for the photolysis at λ 366 nm is 0.99. [ABSTRACT FROM AUTHOR]