title: Catecholase activity of dicopper(II)-bispidine complexes: stabilities and structures of intermediates, kinetics and reaction mechanism.
abstract: A mechanism for the oxidation of 3,5-di-tert-butylcatechol (dtbc) with dioxygen to the corresponding quinone (dtbq), catalyzed by bispidine-dicopper complexes (bispidines are various mono- and dinucleating derivatives of 3,7-diazabicyclo[3.3.1]nonane with bis-tertiary-amine-bispyridyl or bis-tertiary-amine-trispyridyl donor sets), is proposed on the basis of (1) the stoichiometry of the reaction as well as the stabilities and structures [X-ray, density functional theory (B3LYP, TZV)] of the bispidine-dicopper(II)-3,4,5,6-tetrachlorcatechol intermediates, (2) formation kinetics and structures (molecular mechanics, MOMEC) of the end-on peroxo-dicopper(II) complexes and (3) kinetics of the stoichiometric (anaerobic) and catalytic (aerobic) copper-complex-assisted oxidation of dtbc. This involves (1) the oxidation of the dicopper(I) complexes with dioxygen to the corresponding end-on peroxo-dicopper(II) complexes, (2) coordination of dtbc as a bridging ligand upon liberation of H(2)O(2) and (3) intramolecular electron transfer to produce dtbq, which is liberated, and the dicopper(I) catalyst. Although the bispidine complexes have reactivities comparable to those of recently published catalysts with macrocyclic ligands, which seem to reproduce the enzyme-catalyzed process in various reaction sequences, a strikingly different oxidation mechanism is derived from the bispidine-dicopper-catalyzed reaction.
authors.affiliation: Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Born
authors.forename: Peter
authors.initials: P
authors.lastname: Comba
authors.forename: André
authors.initials: A
authors.lastname: Daubinet
authors.forename: Alexander
authors.initials: A
authors.lastname: Fuchs
authors.forename: Hubert
authors.initials: H
authors.lastname: Wadepohl
mesh_terms: D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry*; D002384:Catalysis; D004156:Catechol Oxidase / Q000737:chemistry*; D002396:Catechols / Q000737:chemistry; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D004795:Enzyme Stability; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D002396:Catechols; D009942:Organometallic Compounds; C495809:bispidine; C054068:3,5-di-tert-butylcatechol; D003300:Copper; D004156:Catechol Oxidase; D010100:Oxygen