Pyridine-containing nickel(II) bis-formazanates: Synthesis, structure, and electrochemical study

Abstract

Five diamagnetic nickel(II) complexes with pyridine containing formazans of composition 2L•M were synthesized by slow diffusion. X ray diffraction study of three of these complexes demonstrated that the nickel atoms are coordinated by four nitrogen atoms of two ligands and are in a square planar environment. The nickel atoms lie on inversion centers. The chelate six membered rings Ni-N-N-C-N-N are nonplanar due to noncovalent repulsions between the closely arranged aryl groups. Data from NMR spectroscopy, electronic absorption spec troscopy, and electrochemistry (cyclic voltammetry and rotating disk electrode) show that all complexes have similar structures in solution.In the last third of the 20th century, supramolecular chemistry, which has been earlier the subject of a few studies on selective complexing agents and molecular rec ognition, became a rapidly developing field of chemistry. 1 Extensive studies have been carried out on the chemistry of supramolecular polymers, i.e., high molecular weight compounds composed of repeated low molecular weight fragments linked to each other by noncovalent interac tions. 2 Coordination polymers consisting of an organic molecule and a metal atom/ion as two components, which are linked to each other by a coordination bond, are con sidered by many researchers as promising materials pos sessing the semiconducting, optical, and magnetic prop erties. 3,4 These properties are largely determined by a vir tually infinite series of combinations of inorganic and organic components of structural polymers. However, an empirical search for such combinations becomes increas ingly less advantageous and attractive.Instead of methods based on the use of simple organic ligands, procedures with the use of "complex" ligands in cluding one or several metal atoms have gained increasing acceptance. Complex ligands provide an approach to nu merous structures containing at least two exodentate groups, which can form additional coordination bonds. We will refer to such compounds as metalloligands.The formation of a coordination polymer with the use of metalloligands as building blocks can be represented by Scheme 1, which involves the synthesis of the metallo ligand by the reaction of an organic component L with metal M 1 followed by the reaction of this metalloligand with metal M 2 . Compounds, which can form chelates with the central metal ion with retention of the donor centers directed outward, are commonly used as the or ganic component L. 5-7 Scheme 1Formazans and their complexes are convenient sub strates for the construction of metalloligands due to the presence of a potentially chelating chromophoric group and the possibility of introducing electron donating sub stituents at positions 1, 3, and 5. The deprotonated form of formazan, in which the negative charge is delocalized throughout the conjugated chain, is generally involved in complexation with metal salts to form six membered metal chelates A in which the hydrogen atom is replaced by metal. 8 Complexes with Co II , Ni II , Cu II , Cd...

Reactivity of Two-Electron-Reduced Boron Formazanate Compounds with Electrophiles: Facile N–H/N–C Bond Homolysis Due to the Formation of Stable Ligand Radicals

“…Intrigued by work from the Hicks group on formazanate ligands as nitrogen-rich, redox-active analogues of the well-known β-diketiminates, 26 our group has started a research program to explore the coordination chemistry, redox behavior, and reactivity of complexes with formazanate ligands. 27 Although some early reports on related complexes exist, 28 , 29 it is only recently that interest in this class of ligands has gained momentum. Concurrent with our work, the Gilroy group and others have reported related complexes with formazanate ligands and studied the properties of these compounds 30 , 31 and materials derived thereof.…”

Formazanate coordination compounds: synthesis, reactivity, and applications

“…The majority of these compounds could be obtained as a single isomer by recrystallization, and were shown by X-ray crystallography and NMR spectroscopy to Scheme 11 Formazanate cobalt complexes with o-quinone-based co-ligands and their reduction chemistry. 37,38 40 Tezcan and co-workers reported related Ni complexes, and studied the effect of ligand substituents on the spectroscopic and electrochemical properties. 43 Zaidman et al prepared a series of bis(formazanate) nickel complexes from formazans with various (heteroaromatic) substituents or linked bis-formazan scaffolds, and studied their catalytic activity in ethylene oligomerization (for representative structures 38/39, see Scheme 13b).…”

“…(b) Representative structures of nickel complexes described by Zaidman et al, and their application as catalysts for ethylene oligomerization. [40][41][42][43][44] Scheme 14 (a) Synthesis of homoleptic bis(formazanate) nickel complex 40. (b) Synthesis of heteroleptic cyano/nitro-formazanate nickel hydroxide complexes 41 with larger N-aryl groups.…”

Dinuclear Complexes of Flexidentate Pyridine-Substituted Formazanate Ligands

“…We began our efforts with the new formazan 1,5-bis(p-tolyl)-3-(4-pyridyl)formazan (Fza); closely related derivatives with 1,5-diphenyl substitution have been described, 35 but their coordination chemistry has only been described in one isolated report on homoleptic nickel bisformazanate complexes. 36 Scheme 1 depicts the synthetic route of a mononuclear cyclometalated Ir(III) complex of Fza. Initially we used reaction conditions identical to those outlined in our previous report on cyclometalated iridium formazanate complexes, 31 so our hypothesis was that Fza would chelate the iridium center through the formazanate backbone.…”