Tris{2,4-bis(2-pyridyl)-1,3,5-triazapentanedienato}manganese(III), a complex derived from a unique metal ion-assisted transformation of pyridine-2-amidoxime

Abstract

A novel metal ion-mediated reaction of pyridine-2-amidoxime has led to an 1:3 mononuclear Mn(III) complex containing the 2,4-bis(2-pyridyl)-1,3,5-triazapentanedienate(-1) ligand; the high-spin Mn III in the complex is "EPR silent" at X-band. Upon coordination of a ligand (L) to a metal center (M), the former's properties (acidity, electrophilic or nucleophilic character, susceptibility to reduction or oxidation, etc.) can be significantly altered and therefore its reactivity can be enhanced or inhibited; coordination to M can even enable a reaction that would otherwise not take place. Thus the reactivity chemistry of coordinated ligands is a "hot" research theme in contemporary transition-metal chemistry [1]. Oxime (C═N-OH) and oximate (C═N-O-) groups can bind an M in a variety of coordination modes and are thus ideal candidates for reactivity chemistry [2]. Nucleophilic reagents can add to the C-atom (a reaction that is promoted by coordination of the N-atom), whereas electrophilic reagents can attack the O-or the N-sites [2]. Scheme 1. Structural formulae and abbreviations of the ligands discussed in the text. The initially used ligand is pyridine-2-amidoxime, (py)C(NH 2)NOH, and the anionic ligand present in the Mn(III) complex is 2,4-bis(2-pyridyl)-1,3,5-triazapentanedienate(-1), bptzpd-; py is the general abbreviation for the 2-pyridyl moiety.

Diversity of Coordination Modes in a Flexible Ditopic Ligand Containing 2-Pyridyl, Carbonyl and Hydrazone Functionalities: Mononuclear and Dinuclear Cobalt(III) Complexes, and Tetranuclear Copper(II) and Nickel(II) Clusters

“…Magnetochemistry 2019, 5, x FOR PEER REVIEW 3 of 23 from the synthetic investigation of the CuBr2/LH, Ni(NO3)2•6H2O/LH and Co(ClO4)2•6H2O/LH reaction systems and the characterization of the products obtained. This paper can be considered as a continuation of our interest in the chemistry and magnetism of 3d-metal coordination clusters [9,22], and in the coordination and metal ion-meditated/promoted transformation properties of polydentate ligands containing two or more functionalities (including 2-pyridyl, carbonyl and hydrazone/azine groups, among others) [4,[23][24][25][26][27].…”

Controlling the nuclearity and topology of cobalt complexes through hydration at the ppm level

“…Using various first row transition metal ions (M II ), many of these systems were predicted to exhibit two-step spin-crossover phenomenon. 13 Similar ligand frameworks incorporating pyridyl (N-2pyridylimidoyl-2-pyridylamidine; Py 2 ImAm) or pyrimidyl (N-2pyrimidylimidoyl-2-pyrimidylamidine; Pm 2 ImAm) moieties at the b-position have also been reported; 4,[14][15][16][17] however, here again the ImAm ligands were prepared through metal-assisted transformations using a metal salt and a pyridyl/pyrimidyl synthon. For example, a copper coordination polymer or dimer can be isolated following decomposition of either tris(2pyridyl)triazine 14 or tris(2-pyrimidyl)triazine, 15 respectively, in the presence of copper(II) salts.…”

“…Py 2 ImAm complexes have also been reported through in situ reactions of 2-cyanidopyridine and butan-2-one oxime with PdCl 2 to make a palladium(II) square planar complex, 4 or pyridine-2-amidoxime with MnF 2 resulting in a manganese(III) octahedral complex. 17 While these studies demonstrate the potential of ImAm ligands, a significant drawback lies in their synthesis, which relies on relatively low yielding in situ reactions. 8 Recently, our group developed the synthesis of both Py 2 ImAm 18 and Pm 2 ImAm 19 in large scale without metal ion assistance, thereby enabling us to tailor the reaction conditions in order to selectively bind to the bidentate and/or tridentate coordination sites.…”

Rational Design of Tetranuclear Complexes Employing N‐Imidoylamidine Based Ligands

“…Accessing and controlling coordination to the bidentate and/or tridentate sites within Py 2 ImAm or Pm 2 ImAm would facilitate the development of a variety of metal complexes. Although N ‐imidoylamidines are ideal for the development of polynuclear complexes, few examples exist in literature . This is due in large part to the generation of these ligands, which until recently were only prepared in one pot synthetic procedures through metal‐assisted transformations.…”

“…In both copper complexes, the N ‐imidoylamidine ligand acts to ferromagnetically couple the adjoining Cu II ions, which alternate between different coordination environments. Alternatively, the Py 2 ImAm ligand has also been reported through the in situ reaction between 2‐cyanopyridine and butan‐2‐on oxime with PdCl 2 to make a palladium(II) square‐planar complex, or pyridine‐2‐amidoxime with MnF 2 resulting in a manganese(III) octahedral complex . Since these reports all consisted of one pot synthesis involving metal‐assisted transformations, their formation relied on serendipitous reaction pathways.…”