Square planar versus square pyramidal copper(II) complexes containing N3O moiety: Synthesis, structural characterization, kinetic and catalytic mimicking activity.

Graphical abstract In quest of copper complexes having [CuN 3 O] cores, [Cu(phen)(L –Val)(H 2 O)]NO 3 (1) and [Cu(bpy)(L –Val)]ClO 4 (2) complexes have been synthesized and structurally characterized (phen = 1,10–phenanthroline; bpy = 2,2′–bipyridine). 1 possesses a distorted square-pyramidal, whereas 2 has a distorted square-planar coordination geometry. Structural features of both 1 and 2 reveal the formation of supramolecular networks via inter- and intra-molecular hydrogen bonding interactions. The mechanism of ligand substitution of 1 and 2 by thiourea (TU) is a biphasic process in which an initial fast and dissociative reaction is followed by a slower and associative one. It is concluded from the activation parameters that the difference in structure does not affect the mechanism. Complexes 1 and 2 have also been evaluated as functional models for the catechol oxidase enzyme and phenoxazinone synthese and they are promising candidates as functional mimics for catechol oxidase and phenoxazinone synthase. Highlights • Biomemicking of copper enzymes using mixed NO-ligands. • Effect of the structure on the biomimetic activity. • Stabilization of supramolecular networks via inter- and intra-molecular hydrogen bonding interactions in both complexes. Abstract In quest of copper complexes having [CuN 3 O] cores, [Cu(phen)(l –Val)(H 2 O)]NO 3 (1) and [Cu(bpy)(l –Val)]ClO 4 (2) complexes have been synthesized and structurally characterized (phen = 1,10–phenanthroline; bpy = 2,2′–bipyridine). Complex 1 possesses a distorted square-pyramidal, whereas 2 has a distorted square-planar coordination geometry. Structures of 1 and 2 have supramolecular networks formed via inter- and intra-molecular hydrogen bonding interactions. The kinetics and mechanism of ligand substitution of 1 and 2 by thiourea (TU) were studied in detail and showed a biphasic process in which an initial fast reaction is followed by a slower one. The activation parameters for the fast reaction: Δ H # = 68 ± 4 and 73 ± 5 kJ mol−1, Δ S # = 43 ± 10 and 54 ± 9 J K−1 mol−1 for 1 and 2 , respectively, supports a dissociative substitution mechanism. Whereas for the slow reaction: Δ H # = 33 ± 6 and 43 ± 3 kJ mol−1, Δ S # = −77 ± 10 and −56 ± 9 J K−1 mol−1 for 1 and 2 , respectively, support an associative substitution mechanism. It is concluded from the activation parameters that the difference in structure does not affect the mechanism. Complexes 1 and 2 have also been evaluated as functional models for the catechol oxidase enzyme and phenoxazinone synthase. The model complexes 1 and 2 show catecholase activity of K cat = 10.9 × 103 and 11.4 × 103 h−1 and phenoxazinone synthase activity of K cat = 2.1 × 103 and 4.3 × 103 h−1, respectively. Compared to the enzyme itself (K cat = 8.3 h−1), the model complexes 1 and 2 are promising candidates as functional mimics for catechol oxidase and phenoxazinone synthase. [ABSTRACT FROM AUTHOR]