Pyrazine-2-carboxamide metal complexes

Carboxamides containing alkylamine arms like (34), synthesized from dialkylmalonate and ethylene-diamine, act as chelating dianionic N4-donors,44,45 whereas the geometric isomer (35) was prepared from 1,3-diaminopropane and chloroacetyl chloride.46 The hexadentate bis(pyrazine)-carboxamides (36) and (37) can be obtained by the addition of 1,3-propanediamine to the appropriate carboxylic acid.47 Compound (36), in the dianionic form, can be used to obtain homo- and hetero-metal bridged complexes, whereas (37) has been shown to yield tetranuclear copper(II) complexes involving opened-up dianionic ligand molecules.47... 

Early publications on [VO(/3-diketonato)2] have been reviewed.355 More recently, complexes with benzoyl m-nitroacetanilide, benzoyl acetanilide545 and l,l -(l,3-phenylene)-bis(butane-1,3-dione546 have been synthesized. Other [VO(/S-dik)2] adducts have been isolated, for example [VO(acac)2] adducts with a series of pyridine N-oxides547 and several pyridine carboxamides, 48 and [VO(bzac)2] adducts with pyridine, methylamine, isoquinoline and 4-picoline.549 Equilibrium constants of 1 1 and 2 1 adducts of pyrazine with [VO(tfacac)2] have been determined (equation 38).550 In the 2 1 complex, the pyrazine bridge between two equatorial sites of adjacent vanadium atoms promotes a weak exchange interaction. The nitroxide radical 2,2,6,6-tetramethylpiperidinyl N-oxide also forms an adduct with [VO(hfacac)2] in which there is a strong interaction between the electrons on the metal and nitroxide.551... 

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