Coordinated Hydrazone Ligands as Nucleophiles:  Reactions of Fe(papy)₂

Abstract

The diamagnetic iron(II) complexes of the hydrazone ligand pyridinecarboxaldehyde-2‘-pyridylhydrazone (papyH) have been characterized by NMR, IR, UV−vis, and electrochemistry. The dication Fe(papyH)2 2+ undergoes reversible one-electron oxidation at 0.66 V vs internal ferrocene and shows a strong metal−ligand charge-transfer band in the visible region at 524 nm. Deprotonation with NaOH gives diamagnetic, neutral Fe(papy)2 with an oxidation potential of −0.25 V vs internal ferrocene and a charge-transfer band at 603 nm. Fe(papy)2 reacts with active alkylating agents to give dialkyl complexes Fe(papyR)2 2+ with spectroscopic properties similar to those of Fe(papyH)2 2+. Monitoring the alkylation by UV−vis reveals the intermediacy of a monoalkylated species.

Pyridazine‐Based Ligands and Their Coordinating Ability towards First‐Row Transition Metals

“…[46] Ligand exchange reactions employing metal halide or pseudo-halide precursors are known to lead preferably to complexes of the type metal/ligand = 1:1, [19][20][21][22] whereas employing precursors with noncoordinating counterions leads to complexes of the type 2:1. [18,[24][25][26] Nitrate precursors seem to exhibit reactivity at the borderline, enabling both stoichiometries. Thus, fine-tuning of electronic and steric properties on the pyridazine ring results in two different metal-to-ligand ratios.…”

“…Methylation of the nitrogen atom seemed to be a viable solution without changing the spectroscopic properties of the complexes. [25] These methylated derivatives recently experienced a renaissance as the key building blocks in forming self-assembled morphologies. Complex grid-and rack-type constructions [26][27][28] are induced by dynamic structural and conformational changes of the ligand backbone as described by Lehn and co-workers.…”

Synthesis, Crystal Structure and Electrochemical Studies of a Hydrazone Schiff Base Complex of Titanium(IV)

“…In recent years, the hydrazones have been drawing much attention from coordination chemists, because of the strong tendency of aroyl hydrazones to chelate transition metals [20 -25], lanthanides [26,27], and main group metals [28,29]. It has also been suggested that nucleophilic substitution [30] of hydrazone ligands may be an important route to assemble nanoscale molecular clusters. Qi and Wang [31] have reported the preparation of novel dendritic mixed-valence ruthenium complexes, which can act as variable attenuators for the control of optical signals.…”

Selective extraction of palladium(II) using hydrazone ligand: A novel fluorescent sensor

“…All the complexes were characterized by elemental analyses, stoichiometric studies, FTIR, absorption and emission spectroscopy. In [Pd(L)Cl] the ligand in its anionic form coordinates in a tridentate manner through pyridyl-N, quinoline-N and distal-N of the hydrazine residue [15,20] (Scheme 1)…”