Vanadium complexes macrocyclic ligands

Macrocyclic ligands 1,4,7-triazacyclonona-iV-acetate 221 and iV-(2-hydroxybenzyl)-l,4,7-cyclononane 225 have been prepared from l,4,7-triazacyclio[5.2.1.04 10]decane 40 and were subsequently used for the synthesis of a series of mono- and dinuclear complexes of vanadium(rv) and (v) (Scheme 35) <1995ICA(240)217>. 

N-donor macrocyclic ligands, based on 1,4,7-trithiacyc-lononane and carrying three pendant arms bearing alkoxides give nonoxo vanadium (IV) complexes. ... 

Model compound studies have shown the importance of porphyrin macrocycle basicity, resulting from electron-withdrawing substituents and metal ligands, on the reducibility and susceptibility of the central metal to reaction. Similar insight into the differences in relative basicity of vanadium- and nickel-containing complexes found in petroleum may therefore be valuable in rationalizing the observed effects and predicting demetallation activity. 

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