Tellurium azamacrocycles: synthesis, characterization and coordination studies

Chemistry of selenium/tellurium-containing Schiff base macrocycles

“…The first ever novel selenium and tellurium-containing macrocyclic Schiff base ligands (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) were synthesized in high yield via one-step dipodal condensation of bis(o-formylphenyl) chalcogenides (1-2) and the corresponding diamines without recourse to the metal ion template or high dilution reaction (Scheme 1) [16][17][18][19][20][21]. The reaction is carried out in CH 3 CN at ambient temperature for 24 h to give the [2+2]-macrocyclic azomethines in 32-91% yield.…”

“…The 1 H NMR spectra of the compounds 7-9 and 11 are complex [19]. For compound 7 it is due to the existence of different geometrical and optical isomers whereas for the macrocycles 8, 9 and 11 it is owing to the presence of the mixture of the desired macrocyles along with the isomers formed by the [34,35,28,22] or [28,22] ring contraction as a consequence of the nucleophilic addition of the secondary amine function (NH) across the imine bond.…”

“…Such observations have been reported earlier [24a-e]. The considerable decrease in 77 Se/ 125 Te chemical shift (Table 1) (3,E=Se; 4, E = Te), CH 2 CH 2 CH 2 (5, E = Se; 6, E = Te), CH 2 CH(Me)CH 2 (7, E = Te), CH 2 CH 2 NHCH 2 CH 2 (8, E = Se; 9, E = Te), CH 2 (CH 2 ) 4 CH 2 (10, E = Te ), CH 2 CH 2 NHCH 2 CH 2 NHCH 2 CH 2 (11, E = Te ) and trans-1,2-cyclohexanediyl ( compounds (17)(18)(19)(20)(21) compared to the corresponding Schiff bases, indicates poor shielding of the chalcogen nucleus and a weaker EÁÁÁN interactions in the former. This is due to the sp 3 hybridization of N atoms in the polyamine derivatives compared to the sp 2 hybridization in the parent Schiff bases.…”

“…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.…”

“…However, a similar reaction of the Pd II precursor with the larger 22-membered tellurium analogs 4 (from dialdehyde 2 and ethylenediamine) and 13 (from dialdehyde 2 and trans-1,2-diaminocyclohexane), afforded the desired cationic complexes 33 [19,38] (Fig. 6) and 34 [20], respectively without any macrocyclic ring opening (Scheme 8).…”