Cu(II)‐promoted cyclization of hydrazonophthalazine to triazolophthalazine; Synthesis and structure diversity of six novel Cu(II)‐triazolophthalazine complexes

Abstract

A novel route for the synthesis of Cu(II)-triazolophthalazine complexes using the Cu(II)-promoted cyclization dehydrogenation reactions of hydrazonophthalazines under reflux was presented. Two hydrazonophthalazines were cyclized to the corresponding triazolophthalazine ligands, 3-pyridin-2-yl-3,10b-dihydro- [1,2,4]triazolo[3,4-a]phthalazine (TPP) and 3-(3,10b-dihydro-[1,2,4]triazolo[3,4-a]phthalazin-3-yl)-benzoic acid (TP3COOH), followed by in situ complexation with Cu(II) yielding six novel Cu(II)-triazolophthalazine complexes depending on the reaction conditions. The molecular and supramolecular structures of the Cu(II)-triazolophthalazine complexes were discussed. The metal sites have rectangular pyramidal geometry in the [Cu(TPP)Cl 2 ] 2 ; 1 and [Cu(TP3COOEt)Cl 2 (H 2 O)] 2 ; 4 dinuclear complexes, distorted square planar in [Cu(TP3COOMe) 2 Cl 2 ]; 3, [Cu(TP3COOH) 2 Cl 2 ]; 5 and [Cu(TP3COOH) 2 Cl 2 ]·H 2 O; 6 and a distorted octahedral in [Cu(TPP)(H 2 O) 2 (NO 3 ) 2 ]; 2. Hirshfeld analysis showed that the O…H, C…H, Cl…H (except TP3COOH and 2), N…H and π-π stacking interactions are the most important intermolecular contacts. The π-π stacking interactions are the maximum for TP3COOH and complex 6 with net C…C/C…N contacts of 19.4% and 15.4%, respectively. The orbital-orbital interaction energies of the Cu-N/Cu-Cl bonds correlated inversely with the corresponding Cu-N/Cu-Cl distances, respectively. The charge transfer processes between Cu(II) and ligand groups were also discussed. The charge densities of the Cu(II) centers are reduced to 0.663-0.995 e due to the interactions with the ligand groups coordinating it.

Molecular and Supramolecular Structures of Cd(II) Complexes with Hydralazine-Based Ligands; A New Example for Cyclization of Hydrazonophthalazine to Triazolophthalazine

“…In another instance, the reaction with metal ions with stable oxidation states such as holmium(III), the ligand works as a neutral N-chelator [57]. On the other hand, hydrazonophthalazine underwent oxidative cyclization to the corresponding triazolophthalazines in presence of metal ions having well known catalytic activity such as Cu(II) [58]. In the current work, we presented the reactions of two new hydrazonophthalazine ligands with cadmium chloride as shown in Scheme 1.…”

“…Hydrazonophthalazine ligands are powerful nitrogen chelators due to the availability of different coordinating sites, including the phthalazine and hydrazone nitrogen atoms. This class of ligands can coordinate to the metal ion in different ways depending on the nature of metal ion and reaction conditions [15,57,58]. In the case of easily oxidized metal ions such as Co(II), which can undergo aerobic oxidation in the presence of a strong ligand field, the ligand can lose the labile NH proton and work as a negatively charged Nchelator [15].…”

“…The hydrazonophthalazine ligands (HL and HL OH ) were prepared using the method recently described by our group [15,58]. A mixture of hydralazine-HCl (10 mmol) and sodium acetate (10 mmol) in 50 mL of ethanol was stirred at room temperature for 2 min.…”

“…In our previous work, Schiff bases derived from hydralazine were found to be powerful mononegative [15] or neutral [57] tridentate N-chelators. Moreover, the same ligands underwent Cu(II)-promoted oxidation with cyclization to afford the corresponding triazolophthalazine [58]. In light of the interesting coordination chemistry of Cd(II) and the interesting chelating power of hydrazonophthalazine ligands, which are considered as important topics in the field of crystal engineering [59], the aim of the present work is to shed the light on the molecular and supramolecular structure diversities of novel Cd(II) complexes with the two phthalazine-type ligands (HL and HL OH ) shown in Figure 1.…”