Characterization of the structure and reactivity of monocopper-oxygen complexes supported by beta-diketiminate and anilido-imine ligands.
Copper-oxygen complexes supported by beta-diketiminate and anilido-imine ligands have recently been reported (Aboelella et al., J Am Chem Soc 2004, 126, 16896; Reynolds et al., Inorg Chem 2005, 44, 6989) as potential biomimetic models for dopamine beta-monooxygenase (DbetaM) and peptidylglycine alpha-hydroxylating monooxygenase (PHM). However, in contrast to the enzymatic systems, these complexes fail to exhibit C--H hydroxylation activity (Reynolds et al., Chem Commun 2005, 2014). Quantum chemical characterization of the 1:1 Cu-O(2) model adducts and related species (Cu(III)-hydroperoxide, Cu(III)-oxo, and Cu(III)-hydroxide) indicates that the 1:1 Cu-O(2) adducts are unreactive toward substrates because of the weakness of the O--H bond that would be formed upon hydrogen-atom abstraction. This in turn is ascribed to the 1:1 adducts having both low reduction potentials and basicities. Cu(III)-oxo species on the other hand, determined to be intermediate between Cu(III)-oxo and Cu(II)-oxyl in character, are shown to be far more reactive toward substrates. Based on these results, design strategies for new DbetaM and PHM biomimetic ligands are proposed: new ligands should be made less electron rich so as to favor end-on dioxygen coordination in the 1:1 Cu-O(2) adducts. Comparison of the relative reactivities of the various copper-oxygen complexes as hydroxylating agents provides support for a Cu(II)-superoxide species as the intermediate responsible for substrate hydroxylation in DbetaM and PHM, and suggests that a Cu(III)-oxo intermediate would be competent in this process as well.
Gherman
Benjamin F
BF
Department of Chemistry and Supercomputer Institute, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, USA.
Tolman
William B
WB
Cramer
Christopher J
CJ
D001665:Binding Sites; D002384:Catalysis; D003198:Computer Simulation; D003300:Copper / Q000737:chemistry*; D004299:Dopamine beta-Hydroxylase / Q000737:chemistry; D007097:Imines / Q000737:chemistry*; D008024:Ligands; D006899:Mixed Function Oxygenases / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009097:Multienzyme Complexes / Q000737:chemistry; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*
D007097:Imines; D008024:Ligands; D009097:Multienzyme Complexes; D009942:Organometallic Compounds; D003300:Copper; D006899:Mixed Function Oxygenases; D004299:Dopamine beta-Hydroxylase; C035189:peptidylglycine monooxygenase; D010100:Oxygen