Pyridine-2-carbaldehyde metal complexes

The initial reactions of this type were used to produce copper(II) complexes of salicylaldimines, where additional coordination support is provided by the phenolic oxygen atoms (equation l).10 11 Similar use can be made of pyridine-2-carbaldehyde in the formation of imine chelates. For example, the combination of pyridine-2-carbaldehyde and 2-aminobenzenethiol in the presence of metal ions yields tridentate complexes (Scheme l).12 If the reaction is carried out in the absence of the metal ion, the benzothiazolidine (1) is isolated. Thus the metal ion is essential for the formation of the imine product in this case. Metal complexes of the related tridentate ligands (2),13 (3),14 (4)li and (5)16 can be prepared similarly. 

The synthesis of quadridentate imine chelates usually requires the combination of two equivalents of the carbonyl compound and a diamine, as in the formation of complexes of ligands (6),17 18 (7)19 and (8).20,21 In similar fashion, thermodynamic template reactions allow the very effective synthesis of quinquedentate and sexadentate metal complexes of ligands such as (9),22 (10),23 (ll),24 (12)25 and (13).26 Condensation of 1,1,1-tris(aminomethyl)ethane with pyridine-2-carbaldehyde alone yields... 

The 2-pyridylhydrazone of pyridine-2-carbaldehyde yields tridentate metal complexes which can be deprotonated to neutral complexes (81).175-177 These in turn can be reprotonated, alkylated or acylated on nitrogen and reacted with benzenediazonium fluoroborate on carbon (Scheme 33).178... 

The separation of transition-metal complexes of pyridine-2-carbaldehyde 2-quinolylhydrazone (PAQH) has been accomplished by TLC [63]. The method consists of separation of the metals as their PAQH chelates and quantitation in situ by reflectance spectroscopy. 

A very convenient method for the synthesis of (158) consists in the side-chain bromination of 2-thienyl ethyl ketone followed by reaction with sodium methoxide in methanol and with methanesulphonyl chloride in pyridine, which gave (157) in 88% yield. Treatment of (157) with calcium carbonate led to 1,2-rearrangement of the thienyl group to give (158). Metal complexes of s> -thiophen-2-aldoxime, thiophen-2-carbaldehyde 2-benzothiazolylhydrazone, and thiophen-2-carbaldehyde thiosemicarba-zone have been studied. 

The reduction of ( )-2-, ( )-3- and ( )-4-cinnamoylpyridines by 1,4-dihydropyridines to give dihydro ketones has also been shown to be catalyzed by zinc(II) and magnesium(II).527 Kinetic measurements show that the rate of reduction is fastest in the case of the 2-isomer where the metal is simultaneously complexed with the nitrogen and oxygen donors. A very fast zinc-catalyzed reduction of pyridine-2-carbaldehyde by the alcohol dehydrogenase coenzyme model JV,JV -diethyl-N-benzyl-l,4-dihydronicotinamide (170) has also been described.528... 

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