Functionalized S4Zn (II) complexes as structural modelling for the active site of thiolate-alkylating enzymes: The crystal structure of [TtiZn–SpyH]2·HClO4 [Tti = tris(thioimidazolyl)hydroborate and SpyH = pyridine-2-thiol]

Two new functionalized S3Zn-bound pyridinethiol complexes [TtiZn–SpyH]2·HClO4 1 and [TtiZn–Spy] 2 [Tti = tris(2-mercapto-1-xylyl-imidazolyl)hydroborate, SpyH = pyridine-2-thiol, and Spy = pyridine-4-thiol] were synthesized and characterized. Structural determination of complex 1 showed that the coordination geometry around zinc atom is ideally regular tetrahedral with three thione donors from the ligand Tti and one thiolate donor from the coligand pyridine-2-thiol. The average Zn(1)–S(thione) bond length is 2.349 Å and the Zn(1)–S(thiolate) bond length is 2.289 Å. The reactivity studies of both complexes 1 and 2 as models for the active sites of thiolate-alkylating enzymes toward methylation reactions showed that 1 is much less susceptible to methylation than that of complex 2. This decrease in the nucleophilicity of complex 1 could be explained by electronic effects of the pyridinum salts as well as the steric hindrance, which is provided by the perchlorate anion.