Copper(II) Complexes of Aminocarbohydrate β-Ketoenaminic Ligands: Efficient Catalysts in Catechol Oxidation

• Published in: Chemistry : a European journal Vol. 7; no. 10; pp. 2143 - 2157
• Main Authors: Wegner, Rainer, Gottschaldt, Michael, Görls, Helmar, Jäger, Ernst-G., Klemm, Dieter
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag GmbH 18.05.2001; WILEY‐VCH Verlag GmbH; Wiley
• Subjects: Amino Sugars - chemistry; Amino Sugars - pharmacology; Binding Sites; carbohydrates; Catechol Oxidase; Catechols - metabolism; Chemistry; Chemistry, Multidisciplinary; copper; Copper - chemistry; Kinetics; Ligands; magnetic properties; Molecular Mimicry; Molecular Structure; oxidation; Oxidation-Reduction - drug effects; Physical Sciences; Schiff bases; Science & Technology; carbohydrates; Schiff bases; MOLECULAR-STRUCTURE; CRYSTAL-STRUCTURE; BUILDING-BLOCKS; FUNCTIONAL MODELS; oxidation; ALPHA-AMINO-ACIDS; NICKEL(II) COMPLEXES; REVERSIBLE DIOXYGEN BINDING; magnetic properties; POLYOL-METAL-COMPLEXES; copper; MAGNETIC-PROPERTIES; COBALT(III) COMPLEXES
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/1521-3765(20010518)7:10<2143::AID-CHEM2143>3.0.CO;2-D

Copper(II) complexes of tridentate dianionic β‐ketoenaminic ligands derived from differently functionalized amino‐deoxyglucoses were synthesized and characterized with respect to their structural, spectroscopic, and catalytic properties. The (probably dimeric) complex {1,2‐O‐isopropylidene‐6‐N‐(3‐acetyl‐2‐oxobut‐3‐enyl)amino‐6‐deoxyglucofuranoso}copper(II) Cu(3 a) was a highly efficient catalyst for the catechol‐oxidase‐like oxidation of 3,5‐di‐tert‐butylcatechol (dtbc) into 3,5‐di‐tert‐butylquinone (dtbq) by molecular oxygen (kcat=2.63 s−1). In contrast to this magnetically “normal” complex Cu(3 a), the analogous dinuclear complex [{Cu(2 a)}2], derived from the isomeric amino sugar 5‐amino‐5‐deoxyglucofuranose, forms six‐membered chelate rings with the sugar moiety and has very strong antiferromagnetic‐coupled copper atoms (resulting in a diamagnetic ground state). It has a rather insignificant activity (kcat<10−3 s−1). The ligand H21 a, derived from a (protected) 6‐amino‐6‐deoxyglucopyranose, forms a trinuclear complex [{Cu(1 a)}2⋅Cu(OAc)2] in which two basic formula units are bridged by one copper acetate. This compound and the complex derived from an (isomeric) aminodeoxyglucopyranose ([Cu(4 a)]: kcat≈0.03 s−1) show moderate activity. All complexes with a peripheral ethoxycarbonyl group instead of the acetyl substituent R2, Cu(1 b)–Cu(3 b) and Cu(4 c), are inactive. The complexes derived from 2‐hydroxocyclohexylamine, Cu(5 a) and Cu(5 c), which were used as models of the active complex Cu(3 a), have the typical “cubane‐like” tetranuclear structure known from many copper complexes with derivatives of saturated 2‐aminoalcohols. They are inactive with respect to the activation of dioxygen. Copper complexes of type III (see illustration) that contain tridentate β‐ketoenamine ligands derived from aminodeoxyglucoses, H2N‐R′‐OH, catalyze the oxidation of di‐tert‐butylcatechol to o‐quinone in air. Their activity depends strongly on structural features. Complexes derived from 2‐hydroxycyclohexylamine (R′ = 1,2‐C6H10) instead of the amino sugar are inactive.