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Copper( II ) Complexes of Aminocarbohydrate β ‐Ketoenaminic Ligands: Efficient Catalysts in Catechol Oxidation
Author(s) -
Wegner Rainer,
Gottschaldt Michael,
Görls Helmar,
Jäger ErnstG.,
Klemm Dieter
Publication year - 2001
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 - 10.1002/1521-3765(20010518)7:10<2143::aid-chem2143>3.0.co;2-d
Subject(s) - chemistry , copper , catalysis , ligand (biochemistry) , moiety , catechol , cubane , stereochemistry , catechol oxidase , enzyme kinetics , medicinal chemistry , chelation , substituent , polymer chemistry , crystallography , crystal structure , inorganic chemistry , active site , organic chemistry , enzyme , peroxidase , biochemistry , receptor , polyphenol oxidase
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 ( k cat =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 ( k cat <10 −3 s −1 ). The ligand H 2 1 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 )]: k cat ≈0.03 s −1 ) show moderate activity. All complexes with a peripheral ethoxycarbonyl group instead of the acetyl substituent R 2 , 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.