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Oxidative Double Dehalogenation of Tetrachlorocatechol by a Bio‐Inspired Cu II Complex: Formation of Chloranilic Acid
Author(s) -
Bruijnincx Pieter C. A.,
VicianoChumillas Marta,
Lutz Martin,
Spek Anthony L.,
Reedijk Jan,
van Koten Gerard,
Klein Gebbink Robertus J. M.
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200701878
Subject(s) - chemistry , denticity , ligand (biochemistry) , crystal structure , chloranilic acid , medicinal chemistry , stereochemistry , bridging ligand , copper , crystallography , organic chemistry , biochemistry , receptor
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 Cu II resulted in the complexes [Cu(L1)] n (X) n (X=OTf − , PF 6 − ; 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 Cu II complex was isolated from the reaction of [Cu(L1)] n (PF 6 ) 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, [Cu 2 (ca)Cl 2 (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 [Cu 2 (ca)Cl 2 (HL1) 2 ] resulted in the formation of new pink‐purple mononuclear compound [Cu(ca)(HL1)(H 2 O)], 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.