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Catalytic Cooperativity, Nuclearity, and O 2 /H 2 O 2 Specificity of Multi‐Copper(II) Complexes of Cyclen‐Tethered Cyclotriphosphazene Ligands in Aqueous Media
Author(s) -
Wang Le,
Ye Yong,
Lykourinou Vasiliki,
Yang Junliang,
Angerhofer Alexander,
Zhao Yufen,
Ming LiJune
Publication year - 2017
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201700811
Subject(s) - chemistry , cyclen , copper , cooperativity , catalysis , aqueous medium , aqueous solution , coordination complex , stereochemistry , crystallography , metal , organic chemistry , biochemistry
Three ligands L1 , L2 , and L3 with 2, 4, and 6 1,4,7,10‐tetraazacyclododecane (cyclen) moieties attached to a cyclotriphosphazene core, respectively, were synthesized, and oxidation activities of their Cu II complexes were investigated. Aerobic oxidation of catechol by these complexes follows an intramolecular dinuclear pathway with significant cooperativity (i.e., θ ≈ 1.5 out of a maximum of 2 for two potential substrate binding sites) and kinetic constants (i.e., k cat = 17.5 × 10 –3 s –1 , K m = 2.8 m m , and quite remarkable catalytic specificity k cat / K m 12.5 m –1 s –1 per di‐Cu center), while that by untethered Cu II –cyclen follows a bimolecular dinuclear pathway without noticeable cooperativity ( θ = 0.96) and fourfold lower k cat , despite their similar dinuclear mechanisms. The proximity of Cu II centers is suggested by EPR spectra and relaxations, showing a broad spectral component particularly in Cu 6 L3 . Thermodynamic parameters also indicate the significance of multi‐Cu II sites in the oxidative catalysis. Air is a more specific oxidation agent for the representative complex Cu 2 L1 , showing 3.2‐fold higher catalytic specificity k cat / K m than H 2 O 2 toward a catechol substrate. The research provides further molecular basis for future design of O 2 /H 2 O 2 ‐specific oxidation of multi‐domain Cu complexes.