title: Oxidative double dehalogenation of tetrachlorocatechol by a bio-inspired CuII complex: formation of chloranilic acid.
abstract: Copper(II) complexes of the potentially tripodal N,N,O ligand 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its conjugate acid HL1 have been synthesised and structurally and spectroscopically characterised. The reaction of equimolar amounts of ligand and CuII resulted in the complexes [Cu(L1)]n(X)n (X=OTf-, PF6(-); n=1,2), for which a new bridging coordination mode of L1 is inferred. Although these complexes showed moderate catecholase activity in the oxidation of 3,5-di-tert-butylcatechol, surprising reactivity with the pseudo-substrate tetrachlorocatechol was observed. A chloranilato-bridged dinuclear CuII complex was isolated from the reaction of [Cu(L1)]n(PF6)n with tetrachlorocatechol. This stoichiometric oxidative double dehalogenation of tetrachlorocatechol to chloranilic acid by a biomimetic copper(II) complex is unprecedented. The crystal structure of the product, [Cu2(ca)Cl2(HL1)2], shows a bridging bis-bidentate chloranilato (ca) ligand and ligand L1 coordinated as its conjugate acid (HL1) in a tridentate fashion. Magnetic susceptibility studies revealed weak antiferromagnetic coupling (J= -35 cm(-1)) between the two copper centres in the dinuclear complex. Dissolution of the green complex [Cu2(ca)Cl2(HL1)2] resulted in the formation of new pink-purple mononuclear compound [Cu(ca)(HL1)(H2O)], the crystal structure of which was determined. It showed a terminal bidentate chloranilato ligand and N,N-bidentate coordination of ligand HL1, which illustrates the flexible coordination chemistry of ligand L1.
authors.affiliation: Chemical Biology & Organic Chemistry, Department of Chemistry, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: Pieter C A
authors.initials: PC
authors.lastname: Bruijnincx
authors.forename: Marta
authors.initials: M
authors.lastname: Viciano-Chumillas
authors.forename: Martin
authors.initials: M
authors.lastname: Lutz
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Spek
authors.forename: Jan
authors.initials: J
authors.lastname: Reedijk
authors.forename: Gerard
authors.initials: G
authors.lastname: van Koten
authors.forename: Robertus J M
authors.initials: RJ
authors.lastname: Klein Gebbink
mesh_terms: D016227:Benzoquinones / Q000737:chemistry*; D002396:Catechols / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D006219:Halogens / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D021241:Spectrometry, Mass, Electrospray Ionization; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet
chemical_list: D016227:Benzoquinones; D002396:Catechols; D006219:Halogens; D009942:Organometallic Compounds; C423629:3,4,5,6-tetrachlorocatechol; D003300:Copper; C014400:chloranilic acid