Mechanistic Insight into the Reactivity of Oxotransferases by Novel Asymmetric Dioxomolybdenum(VI) Model Complexes

作者：Mayilmurugan Ramasamy; Harum Bastian N; Volpe Manuel; Sax Alexander F; Palaniandavar Mallayan; Moesch Zanetti Nadia C

来源：Chemistry - A European Journal, 2011, 17(2): 704-713.

DOI：10.1002/chem.201001177

• asymmetric complexes
• density functional calculations
• electrochemistry
• reaction mechanisms
• structure-activity relationships
• transferases

The asymmetric molybdenum(VI) dioxo complexes of the bis(phenolate) ligands 1,4-bis(2-hydroxybenzyl)-1,4-diazepane, 1.4-bis(2-hydroxy-4-methylbenzyl)-1,4-diazepane, 1,4-bis(2-hydroxy-3,5-dimethylbenzyl)-1,4-diazepane. 1,4-bis(2-hydroxy-3,5-ditert-butylbenzyl)-1,4-diazepane, 1,4-bis(2-hydroxy-4-flurobenzyl)-1,4-diaze- pane, and 1,4-bis(2-hydroxy-4-chlorobenzyl)-1,4-diazepane (H(2)(L(1))-H(2)(L(6)), respectively) have been isolated and studied as functional models for molybdenum oxotransferase enzymes. These complexes have been characterized as asymmetric complexes of type [MoO(2)(L)] 1-6 by using NMR spectroscopy, mass spectrometry, elemental analysis, and electrochemical methods. The molecular structures of [MoO(2)(L)] 1-4 have been successfully determined by single-crystal X-ray diffraction analyses, which show them to exhibit a distorted octahedral coordination geometry around molybdenum(VI) in an asymmetrical cis-beta configuration. The Mo-O(oxo) bond lengths differ only by approximate to 0.01 angstrom. Complexes 1, 2, 5, and 6 exhibit two successive Mo(VI)/Mo(V) (E(1/2). -1.141 to -1.848 V) and Mo(V)/Mo(IV) (E(1/2). -1.531 to -2.114 V) redox processes. However, only the Mo(VI)/Mo(V) redox couple was observed for 3 and 4, suggesting that the subsequent reduction of the molybdenum(V) species is difficult. Complexes 1, 2, 5, and 6 elicit efficient catalytic oxygen-atom transfer (OAT) from dimethylsulfoxide (DMSO) to PMe(3) at 65 degrees C at a significantly faster rate than the symmetric molybdenum(VI) complexes of the analogous linear bis(phenolate) ligands known so far to exhibit OAT reactions at a higher temperature (130 degrees C). However, complexes 3 and 4 fail to perform the OAT reaction from DMSO to PMe(3) at 65 degrees C. DFT/B3LYP calculations on the OAT mechanism reveal a strong trans effect.

• 出版日期2011