2,6-Diacetylpyridine, template synthesis

Diacetylpyridine, template synthesis, 21 14 Diacylglycerol, accumulation, lithium and, 36 58... 

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... 

Template synthesis 2,6-diacetylpyridine + 3,3 -diaininodipropylamine + Ni(C104)2 hydrate... 

NiL](PF6)2 N3P D Template synthesis 2,6-diacetylpyridine + PhP(CH2CH2CH2NH2)2 + NiX2 hydrate + NH4PF6 in EtOH SqPI 2825... 

Pyridine-2,6-dicarbaldehyde and 2,6-diacetylpyridine have been widely used in the template synthesis of imine chelates ranging in complexity from linear tridentates, such as (17),38 39 to macrocyclic structures with a range of ring sizes, such as (18).40-42 The in situ formation of macrocyclic ligands of this type depends upon the ring size and the strength of complexation of the triamine by the metal ion at the pH of the reaction. Related complexes with an additional donor atom attached to R2 have been synthesized also.43 44... 

Template reactions of dicarbonyl compounds and diamines have been extended recently to include the dialdehydes (3O)60>61 and (32)62-63 and a range of new diamines such as (31) and (33).64 Examples are shown in equations (6) and (7). The new diamines have also been used in the template synthesis of macrocyclic complexes based on 2,6-diacetylpyridine.60,65... 

Examples of seven-coordination in pyridine-containing macrocycles have also been osberved. Thus the iron(TI) complexes [Fe(L)X,] xhLO (L = 126 X = halide or pseudohalide) are formed923 when the corresponding seven-coordinate iron(lll) complexes are reduced with aqueous sodium dithionite in the presence of excess NaX or by the direct template synthesis with 2,6-diacetylpyridine and the corresponding tetramine in the presence of iron(IJ). The triimine moiety gives rise to a strong... 

Pyridine-2,6-dicarbaldehyde and 2,6-diacetylpyridine have been widely used in the template synthesis of imine chelates ranging in complexity from linear tridentates, such as to... 

The substitution of 3,6-dioxaoctane-l,8-diamine for 3,6-diazaoctane-1,8-diamine in a template synthesis with 2,6-diacetylpyridine on iron(II) yields the mixed donor macrocycle (127). This molecule also forms a seven-coordinate iron(II) complex [Fe(L)(NCS)2] (L = 127). This blue high-spin complex (room temperature magnetic moment = 5.44 BM) exhibits an electronic spectrum and electrochemical behaviour which indicate that the complex of the mixed donor oxygen-containing macrocycle stablizes the -I- 2 oxidation state to a greater extent than the same complex of the corresponding macrocyclic pentamine. The seven-coordinate high-spin iron(TT) complex [Fe(L)(H,0),] (L = 128) of the related macrocycle (128) is formed by the condensation of 2,9-di-(l-methylhydrazino)-l,10-phenanthroline with 2,6-diacetylpyridine in the presence of fresh FeClj HjO. The X-ray crystal structure of this complex clearly shows that the iron(II) atom is coplanar with the macrocyclic donor set. 

Template synthesis 2,6-diacetylpyridine + 2,9-di(l-methyl-hydrazino)- , 10-phenanthroline + Ni(BF4)2 hydrate in H2O... 

Template synthesis 2,6-diacetylpyridine + PhP(CH2CH,CH,NH,), + NiX, hydrate + NHiPF in EtOH... 

In many cases it is possible to utilise the hole size effects for the synthesis of specific types of macrocycle. Thus, a tetradentate macrocycle (6.33) is expected to be obtained from a template condensation of 2,6-diacetylpyridine with 1,5,9-triazanonane in the presence of small, first-row transition metal dications. The hole size of 6.33 closely matches the size of these metal ions. This is indeed what happens when Ni2+ (r = 0.8 A) is used as a template for the condensation and the nickel(n) complex of 6.33 is obtained in good yield (Fig. 6-32). However, when Ag+ (r = 1.0 A) is used as a template, the metal ion... 

In the synthesis of XXXIX when using an Mg(II) template (49), the key reagent is 2,6-diacetylpyridine. The formation of XXXIX is a particularly significant result because in nature Mg(II) is bound to a porphyrin in chlorophyll, and in this reaction Mg(II) has been used successfully to cyclize a nitrogen macrocycle, thereby giving a possible indication of the conditions required for the biological synthesis of chlorophyll. The macrocycles were produced in 40-60% yield in the presence of Mg(II) ions, but in the absence of metal ions the products were of a polymeric nature. 

The in situ synthesis of macrocyclic ligands by condensation of 2,6-diacetylpyridine with polyamines in the presence of metal ions represents one of the early demonstrations of the template effect . Curry and Busch reported the first penta-and hexadentate macrocycles (79 and 80)47), both of which are cyclized in the presence of iron(II) chloride tetrahydrate. The two ligands were isolated as highly... 

Interest in these ligands stems from a desire to synthesize improved analogues of the cobalamines 100). With this in mind, 2,6-diacetylpyridine was condensed with N,N,N- f ra(aminopropyl)amine in the presence of nickel(II) or eopper(II) to afford the complex of 105, Cobalt(II) and zinc(II) have also been employed as templating agents in the synthesis of 105 101). The reaction of the nickel(II) complex of 105 with acetone results in a dimeric complex, 106101), by a process that is well established for primary amines 102). 

An early demonstration of the template effect in the synthesis of macrocyclic ligands was the metal-ion-controlled cyclic condensation of 2,6-diacetylpyridine with 3,3 -diaminodipropylamine to give complexes of the 14-membered N4 ring (118), usually abbreviated (Me2pyo[14]triene i ). Effective template ions include Ni", Co" and Cu". Well-characterized iron complexes have not been... 

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