Bis-tridentate chelates of an asymmetric ligand: X-ray structures and solution NMR characterization of divalent zinc triad metal ion complexes of N-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine

Abstract

Divalent zinc triad metal ion complexes of type M(L)(2)(ClO(4))(2) (L = N-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine) with N(4)S(2) metal coordination spheres were isolated and characterized by X-ray crystallography and variable temperature proton NMR. Although bis-tridentate chelates have nine geometric isomers, the crystallographically characterized complexes of all three metal ions had trans facial octahedral coordination geometry with C(i) symmetry. Despite the low coordination number and geometric preferences of d(10) metal ions, which facilitate inter- and intramolecular exchange processes, dilute solutions of these bis-tridentate chelates exhibited slow geometric isomerization. Symmetry, sterics and shielding arguments supported specific isomeric assignments for the major and minor chemical shift environments observed at low temperature. At elevated temperature, rapid intramolecular exchange occurred for all three complexes but slow intermolecular exchange on the coupling constant time scale was evidenced through detection of J(HgH) interactions for Hg(L)(2) (2+). These unusual observations are discussed in the context of the zinc triad metal ion coordination chemistry of related bis-tridentate chelates.

Zinc triad metal ion complexes ofNN′S ligandN-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine

“…Interestingly, significant broadening at cryogenic temperatures suggests the rate of an intramolecular isomerization process was approaching the chemical shift time scale. However, intramolecular isomerization does not preclude detection of J(M 1 H) [6,7,17]. Proton NMR spectra in alternative solvents were comparable, suggesting negligible solvent involvement in solution equilibria.…”

“…Complexes of diamagnetic zinc triad metals are readily amenable to characterization by NMR, which can often be used to detect coordination equilibria. Although zinc does not have an isotope with favorable NMR properties, previous studies have revealed slow inter-and intramolecular ligand exchange on the NMR chemical shift time scale for zinc triad complexes of multidentate ligands [6]. For Cd(II) and Hg(II) complexes; slow exchange on the typically shorter J( 111/113 Cd 1 H) and J( 199 Hg 1 H) time scales, respectively, may also be observed.…”

“…More recently, we have investigated bis-tridentate chelates of the non-C 2 symmetric ligand N-(2-pyridylmethyl)-N-(2-(methylthio)ethyl)amine (L) (figure 1) with zinc triad perchlorates [6]. In this article, the characterization of 1:1 M(ClO 4 ) 2 and MCl 2 (M ¼ Zn(II), Cd(II), Hg(II)) complexes of L are reported.…”

Plasticity in the copper–thioether bond: Manifestation in blue Cu proteins and in synthetic analogs

“…Other interesting cases include the work of Butcher et al [55,56] where Zn-S distances of 2.50 and 2.60 Å were found.…”

Modification and Optimization of the Bis-picolylamide-Based Relay Protection for Carboxylic Acids to be Cleaved by Unusual Complexation with Cu2+ Salts

“…1-(Pyridin-2-yl)-N-((pyridin-2-yl)methyl)ethanamine (10a): 16 N-(Pyridin-2-yl)-N-((pyridin-2-yl)methyl)benzamide (14). The precursor amine 14a was synthesized by the general procedure a described above.…”