Stereochemical factors and the catalytic activity of tricyclic Cu(II) complexes with tetraaza chelate coresстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:The catalytic activity of tricyclic Cu(II) complexes with tetradentate Schiff bases based on o-aminobenzaldehyde, 1,2-ethylenediamine (I), or 1,4-tetramethylenediamine (II) was studied in the model liquid-phase reaction of cyclohexene oxidation by molecular oxygen. The Schiff bases had tetraaza chelate cores with square-planar and pseudotetrahedral structures. The initial catalytic activity increased when the square-planar structure changed to distorted tetrahedral as agrees with the general trend of allied Cu(II) complexes with bis(oxa, aza) chelate cores. Comparison of the catalytic behavior of Cu(II) chelates of similar spatial structure having different ligand-binding atoms points to the absence of the influence of close neighborhood on the mechanism of cyclohexene oxidation. Chelates with tetraaza cores exhibited higher catalytic activity. In the presence of the square-planar chelate I, the rate of cyclohexene oxidation is not stationary. This property distinguishes I from similar Cu(II) chelates with tetradentate Schiff bases, enaminoketones, or hydrazone imines. The nonstationary oxidation of cyclohexene in the presence of complex II agrees with the model of the rotational isomerization of chelate core, which was discovered earlier for distorted tetrahedral complexes.