Job/Unit: A11265 /KAP1 Date: 02-05-12 18:07:28 Pages: 15 FULL PAPER DOI: 10.1002/ejic.201101265 Copper Complexes of “Superpodal” Amine Ligands and Reactivity Studies towards Dioxygen Anna Jozwiuk, [a] E. Alper Ünal, [a] Stefan Leopold, [a] John P. Boyd, [a] Marco Haryono, [a] Nadine Kurowski, [a] Francisco Velazquez Escobar, [b] Peter Hildebrandt, [b] Jochen Lach, [c] Frank W. Heinemann, [d] Dennis Wiedemann, [a] Elisabeth Irran, [a] and Andreas Grohmann* [a] Keywords: Tetrapodal pentadentate ligands / Copper / Dioxygen / Tyrosinase-like activity / N ligands / Density functional calculations The results of studies focussed on copper complexes of a vari- ety of ligands with an NN 4 donor set are reported. The per- methylated tetrapodal ligand 2 forms a complex with cop- per(I) which, upon reaction with dioxygen at –90 °C, yields a product having a bis(μ-oxido)dicopper(III) core (“O-type” product, 10), as inferred from UV/Vis and resonance-Raman spectroscopic data. The UV/Vis spectrum of 10 has two bands at 300 and 404 nm, with extinction coefficients of 9400 and 10400 L mol –1 cm –1 , respectively. Resonance-Raman spectra display two 16 O/ 18 O-sensitive bands which, based on the isotopic shifts and the absolute frequencies, are attrib- uted to the Cu–O stretching modes of the O-type product. Complex 10 shows tyrosinase-like activity, as its reaction with sodium p-tert-butylphenolate at –90 °C in THF yields p- tert-butylcatechol, in an ortho-hydroxylation reaction (yield: 30%). Two new rigid tetrapodal pentadentate ligands (the “superpods” 3 and 4) can be synthesized by condensation of the primary polyamine 1 with paraformaldehyde. Their cop- Introduction Copper has a particularly rich coordination chemistry, owing to different structural preferences of the di- and monovalent states (Cu II : six-, five- or four-coordinate, often tetragonal; Cu I : four-coordinate, tetrahedral). [1] Because of the operation of the Jahn–Teller effect in its octahedral complexes, copper(II) has been termed a coordination chemical chameleon, [2] with a “plasticity effect” in its stereochemistry. [3] The biological role of copper is essen- tially twofold (with some parallels to that of iron): The metal atom serves as an electron relay (Cu I/II ) when embed- [a] Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany E-mail: andreas.grohmann@chem.tu-berlin.de [b] Max-Volmer-Institut für Biophysikalische Chemie, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany [c] Institut für Anorganische Chemie, Universität Leipzig, Johannisallee 29, 04103 Leipzig, Germany [d] Institut für Anorganische Chemie, Universität Erlangen- Nürnberg, Egerlandstraße 1, 91058 Erlangen, Germany Eur. J. Inorg. Chem. 0000, 0–0 © 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 per(II) complexes (5 and 6) have been spectroscopically char- acterized. As ascertained by X-ray crystallography, 5 has the Cu II ion in a tetragonal-pyramidal environment, with almost uniform Cu–N bond lengths (basal bonds: 2.052 Å and 2.070 Å; apical bond: 2.077 Å). No significant Jahn–Teller distortion is observed here. In 6, the ligand acts as a multinu- cleating donor, which leads to the formation of a ladder-like cluster of [Cu(μ 3 -OH)] units containing a total of two ligands, six copper(II) ions, four hydroxido ligands and eight trifluo- roacetate ions. Two of the trifluoroacetate ions are non-coor- dinating. Variable-temperature magnetic susceptibility data are reported for this hexanuclear copper(II) cluster. Copper(I) complexes of 1 and 3 have been characterized and allowed to react with molecular oxygen, which caused the decompo- sition of the complexes. The IR spectra of the oxygenation products have bands at 1652 and 1632 cm –1 , respectively, which are absent in the spectra of 1 and 3, suggesting that amine functions have been oxidized to imines. ded in specialized polypeptides (e.g. plastocyanin in photo- synthesis), or is the active-site ion (Cu I/II and possibly also Cu III ) in proteins interacting with dioxygen and its metabo- lites. [4,5] Dinuclear examples where the two metal ions work in concert with one molecule of dioxygen are the oxygen carrier haemocyanin and oxidase or oxygenase enzymes such as tyrosinase. [6,7] The latter catalyzes the ortho-hydrox- ylation of phenols to catechols (monophenolase reactivity), as well as the oxidation of catechols to ortho-quinones (di- phenolase activity). A functional catalytic tyrosinase model has recently been described. [8] Dinuclear dioxygen-activa- ting enzymes in which the metal ions function largely inde- pendently of each other include dopamine-β-monooxygen- ase and peptidylglycine-α-hydroxylating monooxygenase. Model complexes for these enzymes are difficult to synthe- size but have been reported. [9,10] Copper sites are often used to illustrate the significance of an “entatic state” during metalloprotein function: The highly specialized polypeptide chain, which provides the metal coordination environment, is so rigid that a change in the redox state of the copper ion, as a consequence of electron transfer and/or substrate