Thiolate alkylation in tripod zinc complexes: a comparative kinetic study.
The biologically relevant alkylations of the thiolate ligands in tripod zinc thiolates by methyl iodide were studied kinetically. Five tripod ligands of the pyrazolyl/thioimidazolyl borate type were employed, offering N3, N2S, NS2, and S3 donor sets. For each of them, the ethyl-, benzyl-, phenyl-, and p-nitrophenylthiolate zinc complexes were investigated, yielding a total of 20 second-order rate constants. The comparison of these rate constants shows three effects: (1) the electronic effect among the thiolates, i.e., the ethanethiolates react about 3 orders of magnitude faster than the p-nitrophenylthiolates; (2) the steric effect among the pyrazolylborates, i.e., the phenyl-substituted ones react about 2 orders of magnitude faster than the tert-butyl-substituted ones; and (3) the strong acceleration by the sulfur donors in the tripods, reaching 4 orders of magnitude between the reaction times of the (N3)Zn-SR and (S3)Zn-SR complexes.
Rombach
Michael
M
Institut für Anorganische und Analytische Chemie der Universität Freiburg, Albertstrasse 21, D-79104 Freiburg, Germany.
Seebacher
Jan
J
Ji
Mian
M
Zhang
Guofang
G
He
Guosen
G
Ibrahim
Mohamed M
MM
Benkmil
Boumahdi
B
Vahrenkamp
Heinrich
H
D000478:Alkylation; D007202:Indicators and Reagents; D007700:Kinetics; D008024:Ligands; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry; D015032:Zinc / Q000737:chemistry*
D007202:Indicators and Reagents; D008024:Ligands; D013438:Sulfhydryl Compounds; D013455:Sulfur; D015032:Zinc