Ligand Effect on Reversible Conversion between Copper(I) and Bis(μ-oxo)dicopper(III) Complex with a Sterically Hindered Tetradentate Tripodal Ligand and Monooxygenase Activity of Bis(μ-oxo)dicopper(III) Complex

• Published in: Inorganic chemistry 2003-12, Vol.42 (25), p.8534-8544
• Main Authors: Mizuno, Masayasu, Hayashi, Hideki, Fujinami, Shuhei, Furutachi, Hideki, Nagatomo, Shigenori, Otake, Shigenori, Uozumi, Kounosuke, Suzuki, Masatatsu, Kitagawa, Teizo
• Format: Article
• Language: English
• Subjects: Algorithms; Chemical Phenomena; Chemistry, Physical; Copper - chemistry; Crystallography, X-Ray; Indicators and Reagents; Ligands; Mixed Function Oxygenases - antagonists & inhibitors; Organometallic Compounds - chemistry; Oxidation-Reduction; Oxygen - chemistry; Spectrum Analysis, Raman; Thermodynamics
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic0345166

A new sterically hindered tetradentate tripodal ligand (Me2-etpy) and its labeled analogue having deuterated methylene groups (d 4-Me2-etpy) were synthesized, where Me2-etpy is bis(6-methyl-2-pyridylmethyl)(2-pyridylethyl)amine. Copper(I) complexes [Cu(Me2-etpy or d 4-Me2-etpy)]+ (1 and 1 -d 4, respectively) reacted with dioxygen at −80 °C in acetone to give bis(μ-oxo)dicopper(III) complexes [Cu2(O)2(Me2-etpy or d 4-Me2-etpy)2]2+ (1-oxo and 1 -d 4-oxo, respectively), the latter of which was crystallographically characterized. Unlike a bis(μ-oxo)dicopper(III) complex with a closely related Me2-tpa ligand having a 2-pyridylmethyl pendant, 1-oxo possessing a 2-pyridylethyl pendant is not fully formed even under 1 atm of O2 at −80 °C and is very reactive toward the oxidation of the supporting ligand. Thermal decomposition of 1-oxo gave an N-dealkylated ligand in yield ∼80% based on a dimer and a corresponding aldehyde. The deuterated ligand d 4-Me2-etpy greatly stabilizes the bis(μ-oxo)dicopper(III) complex 1 -d 4-oxo, indicating that the rate determining step of the N-dealkylation is the C−H bond cleavage from the methylene group. The reversible conversion between 1 -d 4 and 1 -d 4-oxo in acetone is dependent on the temperature, and the thermodynamic parameters (ΔH and ΔS) of the equilibrium were determined to be −53 ± 2 kJ mol-1 and −187 ± 10 J mol-1 K-1, respectively. The effect of the 2-pyridylethyl pendant in comparison with the 2-pyridylmethyl and 6-methyl-2-pyridylmethyl pendants on the physicochemical properties of the copper(I) and bis(μ-oxo)dicopper(III) species is discussed.