The Ligation Properties of some Reduced Schiff Base Selena/Telluraaza Macrocycles: Versatile Structural Trends

Abstract

The chalcogenaaza macrocycles 4, 5 and 6 show versatility in ligation properties towards various transition metal ions. The structure of the reduced 22-membered selenaaza macrocycle 4 (C 32 H 36 N 4 Se 2 ) has been determined. The Ni II complex 7 exhibits coordination by the N4Se2 donor sites. The Pd II complexes 8, 9, 10, and 14 have been structurally characterized. The molecular structures of these complexes reveal interesting versatile ligating behaviors of the ligands. The Pd complexes 8, 9, and 14 display coordination by hard nitrogen donor atoms only, whereas the complex 10 showed coordina-

Structural aspects of some organoselenium compounds

“…However, the chemical shift for 7 is significantly upfield shifted compared to the corresponding selenenylsulfide (625 ppm) derived from 2-pheny-2-oxazine [3]. The spiroselenurane 8 was obtained serendipitously during the protonation of selenaazamacrocycles with phosphoric acid [14]. Compound 8 presumably results from the oxidation of precursor bis(o-formylphenyl) selenide [15].…”

Chemistry of selenium/tellurium-containing Schiff base macrocycles

“…The formation of the 1:1 metal-ligand complex 36 [32,40], from the reaction of Pd(II) precursors with 17 (Scheme 9), is in contrast to the formation of hydrolyzed product 31 [18] from the parent Schiff base 3 (Scheme 8). Ligand 17 [32], the reduced analog of 3, being larger than 3 (Table 2), can accommodate Pd 2+ . A study of 77 Se NMR (downfield shifts of 36a (869 ppm) and 36b (787 ppm) compared to the free ligand 17 (Table 1)) gives evidence of Pd-Se coordination in solution.…”

“…It has been noticed that the Schiff base Ni(II) complexes (26)(27)(28)(29) are red-brown to greenish yellow in color and paramagnetic (Scheme 6), [18][19][20] whereas the reduced macrocycles (Scheme 7) afforded purple (30) and blue (from 20 and Ni(II)) colored paramagnetic complexes [32,33]. Except for difference in color all the Ni(II) complexes of the selenaaza-and telluraza macrocyles have similar electronic and magnetic properties.…”

“…The Pd(II) complex 37 is prepared from the reaction of PdCl 2 and 18 (corresponding tetraamine of 4) (Scheme 9) [32,38]. The single 125 Te peak at 710 ppm disappeared after half an hour due to decomposition of the complex in DMSO-d 6 .…”

Hypercoordinated organoselenium compounds with O→Se intramolecular interactions

“…In organoselenium compounds the N→Se intramolecular interaction was observed to reduce the Lewis acidity and to increase the electrophilic reactivity of the chalcogen atom, thus making it more suitable for additional Se→M coordination. In this way, organoselenium compounds bearing organic groups with potential for building hypercoordinated species become useful multidentate ligands using both hard (O, N) and soft (Se) donor atoms [5][6][7][8][9][10].…”