title: Fast O2 binding at dicopper complexes containing Schiff-base dinucleating ligands.
abstract: A new family of dicopper(I) complexes [CuI2RL](X)2 (R=H, 1X, R=tBu, 2X and R=NO2, 3X, X=CF3SO3, ClO4, SbF6, or BArF, BArF=[B{3,5-(CF3)2C6H3}4]-), where RL is a Schiff-base ligand containing two tridentate binding sites linked by a xylyl spacer, has been prepared and characterized, and its reaction with O2 has been studied. The complexes were designed with the aim of reproducing structural aspects of the active site of type 3 dicopper proteins; they contain two three-coordinate copper sites and a rather flexible podand ligand backbone. The solid-state structures of 1ClO4, 2CF3SO3, 2ClO4, and 3BArF.CH3CN have been established by single-crystal X-ray diffraction analysis. 1ClO4 adopts a polymeric structure in the solid state while 2CF3SO3, 2ClO4, and 3BArF.CH3CN are monomeric. The complexes have been studied in solution by means of 1H and 19F NMR spectroscopy, which put forward the presence of dynamic processes. 1-3BArF and 1-3CF3SO3 in acetone react rapidly with O2 to generate metaestable [CuIII2(mu-O)2(RL)]2+ 1-3(O2) and [CuIII2(mu-O)2(CF3SO3)(RL)]+ 1-3(O2)(CF3SO3) species, respectively, that have been characterized by UV-vis spectroscopy and resonance Raman analysis. Instead, reaction of 1-3BArF with O2 in CH2Cl2 results in intermolecular O2 binding. DFT methods have been used to study the chemical identities and structural parameters of the O2 adducts, and the relative stability of the CuIII2(mu-O)2 form with respect to the CuII2(mu-eta2:eta2-O2) isomer. The reaction of 1X, X = CF3SO3 and BArF, with O2 in acetone has been studied by stopped-flow UV-vis exhibiting an unexpected very fast reaction rate (k=3.82(4)x10(3) M-1 s-1, DeltaH=4.9+/-0.5 kJ.mol-1, DeltaS=-148+/-5 J.K-1.mol-1), nearly 3 orders of magnitude faster than in the parent [CuI2(m-XYLMeAN)]2+. Thermal decomposition of 1-3(O2) does not result in aromatic hydroxylation. The mechanism and kinetics of O2 binding to 1X (X=CF3SO3 and BArF) are discussed and compared with those associated with selected examples of reported models of O2-processing copper proteins. A synergistic role of the copper ions in O2 binding and activation is clearly established from this analysis.
authors.affiliation: Departament de Química and Institut de Química Computacional, Universitat de Girona, Campus de Montilivi E-17071, Girona, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Company
authors.forename: Laura
authors.initials: L
authors.lastname: Gómez
authors.forename: Rubén
authors.initials: R
authors.lastname: Mas-Ballesté
authors.forename: Ivan V
authors.initials: IV
authors.lastname: Korendovych
authors.forename: Xavi
authors.initials: X
authors.lastname: Ribas
authors.forename: Albert
authors.initials: A
authors.lastname: Poater
authors.forename: Teodor
authors.initials: T
authors.lastname: Parella
authors.forename: Xavier
authors.initials: X
authors.lastname: Fontrodona
authors.forename: Jordi
authors.initials: J
authors.lastname: Benet-Buchholz
authors.forename: Miquel
authors.initials: M
authors.lastname: Solà
authors.forename: Lawrence
authors.initials: L
authors.lastname: Que
authors.forename: Elena V
authors.initials: EV
authors.lastname: Rybak-Akimova
authors.forename: Miquel
authors.initials: M
authors.lastname: Costas
mesh_terms: D003300:Copper / Q000737:chemistry*; D007700:Kinetics; D008024:Ligands; D008667:Metalloproteins / Q000737:chemistry*; D018716:Molecular Mimicry; D019906:Nuclear Magnetic Resonance, Biomolecular; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D012545:Schiff Bases / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: D008024:Ligands; D008667:Metalloproteins; D009942:Organometallic Compounds; D012545:Schiff Bases; D003300:Copper; D010100:Oxygen