2.6- Diacetylpyridine

From 2,6-diacetylpyridine dioxime, ferric chloride hydrate, and phenylboronic acid as starting materials the macrocyclic dinuclear iron(ll) complexes 133 can be prepared (Fig. 36). 

While iron(III) complexes of thiosemicarbazones with different functional groups involving have been prepared from 2-acetylpyridine, substitution on the ring has been more popular with thiosemicarbazones derived from 2-formylpyridine. The only thiosemicarbazones in which the 2-acetylpyridine ring has been substituted are 15a and 15b, prepared from 6-methyl-2-acetyl-pyridine [120]. Both of these iron(III) complexes have rhombic spectra and values of g, are similar to those found for the 2-acetylpyridine thiosemicarbazones. Solution studies have been carried out on the iron(III) complex of 2,6-diacetylpyridine mono-thiosemicarbazone, but the solid complex was not isolated [143]. 

When a methanol solution containing a 1 1 molar ratio of cobalt(II) chloride to 2,6-diacetylpyridine bis(thiosemicarbazone), 28, is refluxed, [Co(28)Cl]Cl is formed [147]. Spectral studies indicate bonding as a SNNNS pentadentate... 

Diacetylpyridine bis(S-methylisothiosemicarbazone), 46, formed [Co(46-H)l2] H20 from a mixture of cobalt(II) acetate, 46, and hydrogen iodide in heated ethanol [203]. The complex is 7-coordinate with 46 functioning as a NNNNN pentadentate ligand. 

Solution studies of nickel(II) complexes of 2,6-diacetylpyridine bis(thiosemi-carbazone), 28, have been carried out [147]. From a refluxed methanolic solution containing 28 and nickel(II) chloride, [Ni(28)Cl2] was isolated which behaved as a 1 1 electrolyte in methanol [152], Based on spectral information it is proposed that the complex is a distorted octahedron with a SNNNS pentadentate ligand. 

A series of paramagnetic [NiL-2H] complexes have been isolated in which L = 2,6-diacetylpyridine bis(azacyclothiosemicarbazones) with Ni(II) assuming a distorted five-coordinate structure with d-d bands at about 7250, 10510, 12500, 14400, 19200 and 20500 cm [153], None of these Ni(II) complexes were reported to have activity against the P388 lymphocytic leukemia test system in mice. 

Diacetylpyridine bis(S-methylisothiosemicarbazone), 46, yields five-coordinate [Ni(46-H)]X (X = I, NCS) and six-coordinate [Ni(46-2H)] [203]. The latter compound is thought to be dimeric or polymeric with octahedral nickelfll) centers. 

Ligand abbreviations bi = 2,2 -bi-2-imidazoline bt = 2,2 -bi-2-thiazoline bpy = 2,2 -bipyridine phen = 1,10-phenanthroline phy = l,10-phenanthroline-2-carbaldehyde phenylhydrazone bpp = 2,6-bis(pyrazol-3-yl)pyridine paptH = 2-(2-pyridylamino)-4-(2-pyridyl)thiazole 2-pic = 2-picolylamine L = macrocyclic ligand derived from condensation of 2,6-diacetylpyridine with 3,6-dioxaoctane-1,8-diamine Hjthpu = pyruvic acid thiosemicarbazone Hjthpx = pyridoxal thiosemicarbazone salen = dianion of W,iV -ethylenebis(salicylideneimine) H2fsa2en = dianion of fV,JV -ethylenebis(3-carboxysalicylaldimine). 

Bis(semicarbazones) with N202 donor set form six-coordinate complexes with distorted octahedral geometry. The well-studied (potentially pentadentate) 2,6-diacetylpyridine bis(semicarbazone) (H2daps, 448) forms two type of crystals containing the same complex [Ni(Hdaps)2].1267 The ligands are coordinated through their pyridine and the inline N atoms and the O atom of one arm. 

Silver(I) complexes with macrocyclic nitrogen ligands are also very numerous. Mono- or homodi-nuclear silver-containing molecular clefts can be synthesized from the cyclocondensation of functionalized alkanediamines or triamines with 2,6-diacetylpyridine, pyridine-2,6-dicarbalde-hyde, thiophene-2,5-dicarbaldehyde, furan-2,5-dicarbaldehyde, or pyrrole-2,5-dicarbaldehyde in the presence of silver(I).486 97 The clefts are derived from bibracchial tetraimine Schiff base macrocycles and have been used, via transmetallation reactions, to complex other metal centers. The incorporation of a range of functionalized triamines has provided the conformational flexibility to vary the homodinuclear intermetallic separation from ca. 3 A to an excess of 6 A, and also to incorporate anions as intermetallic spacers. Some examples of the silver(I) complexes obtained are shown in Figure 5. 

Studies involving 2,6-diacetylpyridine derivatives. Detailed studies by Nelson and coworkers supported by X-ray structural work by Drew and coworkers have elucidated many aspects of the template synthesis of metal complexes of a Schiff-base ligand series which includes the N4-donor system (83) and the N5-systems (84)-(86) (Nelson, 1980). Since... 

Condensation of 2,6-diacetylpyridine with bis(3-aminopropane)amine in the presence of small ions such as Mn(n), Co(n), Ni(n) or Cu(n) readily leads to formation of the corresponding monomeric (14-membered) macrocyclic complexes of ligand (83). However, when the large Ag(i) ion is used as the template, then a dimetallic complex of a 28-membered macrocycle of type (88) is produced. This example illustrates well the importance of metal-ion size in promoting template reactions. 

Transition Metal Complexes with Bis(Hydrazone) Ligands of 2, 6-Diacetylpyridine. Hepta-Coordination of 3d Metals... 

Unsymmetrical2,6-bis(arylimino)pyridines (Fig. 2), [2-(ArN=CMe)-6-(Ar,N=CMe) C5H3N] (2), are prepared by the successive condensation reactions of 2,6-diacetylpyri-dine with two different anilines [36, 22, 34, 59, 60, 70], For example, the mixed mesityl/m-xylyl derivative is prepared by firstly treating 2,6-diacetylpyridine with... 

In contrast, the related diamines 45 and 46 [cf. (3,5-/-Pr2C6H2-4-NH2)2CH2 above] give, on treatment with 2,6-diacetylpyridine, oligomeric polyimines that can be readily complexed with iron dichloride to afford 47 and 48, respectively (Fig. 14). Notably, on activation with MAO, 47 and 48 are active catalysts for ethylene polymerisation and indeed perform more efficiently at elevated temperatures than those of the original bis(imino)pyridine iron precatalyst 5 [166],... 

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