A bioinspired tris(thioimidazolyl)borate zinc(II) thiolato complex as a structural and functional mimic for sulfur-containing metalloenzymes

A new tripodal zinc(II) benzylthiolato complex, S3iprZn–SCH2Ph (1-S4) [S3ipr = hydrotris(N-(2,6-diisopropylphenyl)-2-thioimidazolyl)borate], was synthesized from the singly µ-hydroxo-bridged precursor {[S3iprZn]2(μ-OH)}+ (1-OH), whose distorted tetrahedral S3O coordination environment was confirmed by single-crystal X-ray diffraction. Complex 1-S4 was characterized by elemental analysis, FT-IR, and 1H NMR spectroscopes. Its reaction with methyl iodide was investigated by preparative and time-resolved 1H NMR spectroscopy, revealing quantitative formation of benzyl methyl thioether and the zinc iodide complex S3iprZn–I (1-I) via direct SN2 alkylation of the coordinated thiolate. The reaction followed pseudo-first-order kinetics under excess methyl iodide, with the observed rate constants showing a linear dependence on methyl iodide concentration, consistent with an overall second-order rate constant of 3.07 × 10−2 M−1s−1. Compared with related zinc thiolate complexes supported by mixed-donor NS2, N2S, and N3 ligands, the sulfur-rich tris(thioimidazolyl)borate scaffold exhibits markedly enhanced alkylation reactivity, highlighting its ability to increase thiolate nucleophilicity and modulate Zn–S bond reactivity.