Metal complexes with four macrocyclic ligands derived from 2,6bis(2-formylphenoxymethyl)pyridine and 1,7-bis (2-formylphenyl)-1,4,7-trioxaheptane

bis[2-(Dimethylaminomethyl)pyrrolyl]tantalum chloride (1) was prepared by treatment of the TaCl5 with 2 equiv. of [2(dimethylaminomethyl)pyrrolyl]lithium. The solid state structure of 1 shows the seven-coordinated tantalum atom, with a geometry corresponding to a pentagonal bipyramidal structure, in which two chlorine atoms occupy the axial position with the angle of 174.8(2)°. Furthermore, variable-temperature 1H NMR spectra infer the fluxionality of the two chelating pyrrolyl ligands with an estimated energy barrier of 13.8 kcal mol-1. Compound 1 shows no catalytic activity toward ethylene polymerization even activated with MAO.