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Thiolate alkylation in tripod zinc complexes: a comparative kinetic study
Michael Rombach1, Jan Seebacher, Mian Ji
1Institut für Anorganische und Analytische Chemie der Universität Freiburg, Albertstrasse 21, D-79104 Freiburg, Germany.
Inorganic Chemistry
|May 23, 2006
Summary
This study investigated the kinetic alkylation of zinc complexes with thiolate ligands. Sulfur donors in tripod ligands significantly accelerate reactions, with electronic and steric factors also influencing reaction rates.
Area of Science:
- Organometallic Chemistry
- Coordination Chemistry
- Reaction Kinetics
Background:
- Tripod ligands are crucial in coordination chemistry, influencing metal center reactivity.
- Zinc thiolates are relevant in biological systems and catalysis.
- Understanding ligand effects on alkylation kinetics is vital for designing new catalysts.
Purpose of the Study:
- To kinetically study the alkylation of zinc thiolate complexes with methyl iodide.
- To investigate the influence of different tripod ligand donor sets (N3, N2S, NS2, S3) on reaction rates.
- To elucidate the electronic and steric effects of thiolate substituents and ligand structure on reaction kinetics.
Main Methods:
- Synthesis of five pyrazolyl/thioimidazolyl borate tripod ligands.
- Preparation of zinc complexes with ethyl-, benzyl-, phenyl-, and p-nitrophenylthiolate ligands.
- Kinetic analysis of the alkylation reactions using methyl iodide, determining 20 second-order rate constants.
Main Results:
- Ethanethiolates reacted approximately 1000 times faster than p-nitrophenylthiolates due to electronic effects.
- Phenyl-substituted pyrazolylborates reacted approximately 100 times faster than tert-butyl-substituted ones, showing steric influence.
- Sulfur donors in tripod ligands accelerated reactions by up to 10,000-fold compared to nitrogen-only ligands.
Conclusions:
- The electronic nature of the thiolate ligand significantly impacts alkylation rates.
- Steric bulk on the tripod ligand influences the reaction kinetics.
- The presence of sulfur donors in tripod ligands dramatically enhances the alkylation rate of zinc thiolates, offering a pathway for catalyst design.
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