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Structural Evidences for the Oxidation of α‐Hydroxycarboxilic Acids to Oxalate Assisted by Copper(II) Ions
Author(s) -
Castiñeiras Alfonso,
Balboa Susana,
Carballo Rosa,
GonzálezPérez Josefa María,
NiclósGutiérrez Juan
Publication year - 2007
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.200600362
Subject(s) - oxalate , chemistry , crystallography , copper , crystal structure , octahedron , hydrogen bond , diimine , ligand (biochemistry) , stacking , protonation , stereochemistry , ion , inorganic chemistry , molecule , catalysis , organic chemistry , biochemistry , receptor
The mono‐, di‐ or poly‐nuclear copper(II)‐oxalate complexes [Cu(phen)(ox)(H 2 O)]·H 2 O ( 1 ), {[Cu( μ ‐ox)(bpy)]·H 2 O· 1/2EtOH} n ( 2 ), {[Cu( μ ‐ox)(bpy)]·2H 2 O} n ( 3 ), [{Cu(NO 3 )(bpy)(H 2 O)} 2 ( μ ‐ox)] ( 4 ) and [{Cu(NO 3 )(phen)(H 2 O)} 2 ( μ ‐ox)] ( 5 ) (ox = oxalato, phen = 1,10‐phenanthroline y bpy = 2,2′‐bipyridine) were prepared by reacting Cu 2 CO 3 (OH) 2 ·2H 2 O or Cu(NO 3 ) 2 ·3H 2 O salts with glycolic (H 2 GLYO) or lactic (H 2 LACO) acids or D‐gluconic acid δ‐lactone (δ‐gluconolactone, H 2 δ‐Glc) in presence of diimine ancillary ligands. Their crystal structures are reported. The copper(II) atom exhibits a 4+1 five‐coordinate CuN 2 O 2 O′ environment in 1 , a 4+2 elongated rhombic octahedral CuN 2 O 2 O′ 2 stereochemistry in 2 or 3 , and a 4+1+1 tetragonally elongated octahedral Cu 2 N 2 O 2 O′O″ surrounding in 4 or 5 . The ligand arrangement and the packing of 5 seem to be strongly influenced by intra‐ and inter‐molecular hydrogen bonding as well as π,π‐stacking interactions between C 6 ‐rings from adjacent phen ligands. The most striking feature now reported is the Cu II ‐mediated oxidation of GLYO 2− , LACO 2&−; or δ‐Glc 2&−; leading to the formation of corresponding Cu II ‐oxalate derivatives. For the glycolate case a mechanism involving a cleavage of the α‐C‐H bonds is proposed, whereas for lactate or D‐gluconate related systems an oxidative degradation through C‐C bond cleavage are assumed.