Stereospecific Deuteration of Chelated 2,2′-Thiodiacetate(tda) in [Co(dien)(tda)]+ (dien = diethylenetriamine) Observed in the Acidic D2O Solutions

Abstract

Stereospecific deuteration rates of 2,2′-thiodiacetate (tda) in s-fac- and u-fac-[Co(dien)(tda)]+ were measured at 70.2 °C in D2O (pD range 4.4 – 6.4). The observed rate constants (k′) were proportional to the [OD−]. The large k′/[OD−] value (ca. 3.8 × 106) shows that the protons on the chelated -SCH2COO− ring are much more active than those on the chelated -NHCH2COO− ring.

Three-Membered −SCoCH2 Chelate Ring Complex Formed by Photodecarboxylation Reaction of Optically Active trans(O)-[Co(edtda)(en)]Cl (edtda = Ethylenedithiodiacetate)

“…Finally (after 30 min), this AB quartet disappeared completely to form the −SCD 2 COO−, and only the A 2 B 2 pattern signal remained. Although similar 1 H NMR spectral changes were also observed for the t -[Co(CH 3 SCH 2 COO)(tren)] 2+ (tren = tris(2-aminoethyl)amine) 5a, and [Co(edma) 2 ] + (edma = ethylenediamine- N -acetate) complexes, such a rapid H−D exchange reaction is peculiar. In complex 2 , the two inequivalent −SCH 2 COO - protons appear at δ = 3.27 and 3.50 ( J = 12 Hz) as an AB quartet.…”

“…As the attempted optical resolution of 2 was unsuccessful using the method of a column chromatographic technique and/or using the optically active anion, further, it is clear that the chiral inversion of S atoms of 2 is rapid even in the acidic solution. Though epimerization of the coordinated chiral thioether S atoms has been previously reported for p -[Co(CH 3 S(CH 2 ) 2 NH 2 )(tren)] 3+ 2f,15 and t -[Co(CH 3 SCH 2 COO)(tren)] 2+ , 5a,11c, there is no example such chiral inversion on the tertiary S atoms in the three-membered ring. However, it is difficult to define whether the racemization of 2 occurred during the course of the photoreaction or after that.…”

“…In complex 2 , the two inequivalent −SCH 2 COO - protons appear at δ = 3.27 and 3.50 ( J = 12 Hz) as an AB quartet. The spectra of 2 indicated that the H−D exchange reaction in the facially coordinated −CH 2 S(CH 2 ) 2 SCH 2 COO - also occurred, but the deuteration rate was much slower than 1 and other thiocarboxylato complexes (Figure c,d) . It is thought that the less activation in the deuteration of the methylene protons in 2 is attributable to the long Co−O bond distance, which is due to the trans influence from the coordinated CH 2 group (vide supra).…”

“…Many cobalt(III)−sulfide complexes have been extensively investigated in view of their stereochemistries, kinetics of ligand substitution, and electron-transfer reactions. , Recent reports have revealed that the thioether sulfur atom to the coordinated cobalt(III) ion induces remarkable effects upon the reversible rearrangement from a S- to a C-bonded complex in basic solutions and deuteration of the methylene protons adjacent to the coordinated thioether group in D 2 O solutions. , Further, the methylcobalamin-dependent enzyme catalyzes the reaction converting homocysteine to methionine . Reactions of analogous model systems have been used to address various aspects of thiolate organocobalt(III) vitamin B 12 chemistry .…”