34297-27-3Relevant articles and documents
Bis-cis-dioxomolybdenum(VI), 2>; Structure and Spectroscopic Studies
Buchanan, Iain,Garner, C. David,Clegg, William
, p. 1333 - 1342 (1984)
The complex 2> crystallises in the monoclinic space group P21, with a=11.794(2), b=12.519(3), c=13.040(2) Angstroem, β=106.32(2) deg, and Z=4.The structure was solved from 5 502 unique observed reflections, and refinement gave a final R of 0.039; anomalous dispersion was employed to verify the absolute configuration at molybdenum and at the chiral carbon of the ligands.The two crystallographically independent molecules have opposite absolute configurations (Λ and Δ) for the ligand chelate rings about the metal; the expected cis-dioxo-stereochemistry is confirmed, with normal bond lengths .Proton, 13C, and 95Mo n.m.r. spectra are consistent with these two diastereoisomeric molecules persisting in solution, and together with c.d. data are taken to indicate that, for the (S)-ligand complex in (CD3)2SO at ca. 298 K, the Λ isomer is present in a ca. 2:1 excess over the Δ isomer, the reverse being the case for the (R)-ligand complex.The two diastereoisomers are in dynamic equilibrium and 1H n.m.r. data collected over the temperature range 297-385 K indicate that the activation parameters for the Λ-->Δ interconversion are ΔH(excit.)=44+/-6 kJ mol-1 and ΔS(excit.)=-110+/-17 J K-1 mol-1.The mechanism for the inversion of configuration at molybdenum is considered to proceed by an intramolecular process, involving Mo-N bond rupture followed by rotation of the ligand atoms of the subsequent intermediate and ring closure.C.d. spectra resolve each of the u.v.-visible absorption bands centred at ca. 264 and 352 nm into two components.The i.r. active ν(Mo-Ot) stretching vibrations of cis-2> are manifest as a pair of doublets at 918/913 and 878/875 cm-1, presumably due to the Λ and Δ isomers having slightly different ν(Mo-Ot) values.
D-Penicillamine and L-cysteine derived thiazolidine catalysts: an efficient approach to both enantiomers of secondary alcohols
Serra, M. Elisa Silva,Costa, Dora,Murtinho, Dina,Tavares, Nélia C.T.,Pinho e Melo, Teresa M.V.D.
, p. 5923 - 5927 (2016/09/07)
D-Penicillamine derived thiazolidine ligands were prepared in a two-step synthetic sequence and used in the enantioselective alkylation of a variety of aromatic aldehydes with diethylzinc at room temperature. Excellent ee, up to >99%, and nearly complete conversions were observed. Structurally analogous L-cysteine derived thiazolidine ligands were also synthesized and tested for comparative purposes, resulting in very good, albeit slightly lower selectivities, up to 89%. The combined use of these two types of thiazolidines constitutes a very interesting strategy for synthesizing both (S) and (R) enantiomers of chiral secondary alcohols, thus leading the way to a myriad of useful optically active products with opposite absolute configurations.
The species- and site-specific acid-base properties of penicillamine and its homodisulfide
Mirzahosseini, Arash,Szilvay, András,Noszál, Béla
, p. 62 - 69 (2014/08/18)
Penicillamine, penicillamine disulfide and 4 related compounds were studied by 1H NMR-pH titrations and case-tailored evaluation methods. The resulting acid-base properties are quantified in terms of 14 macroscopic and 28 microscopic protonation constants and the concomitant 7 interactivity parameters. The species- and site-specific basicities are interpreted by means of inductive and shielding effects through various intra- and intermolecular comparisons. The thiolate basicities determined this way are key parameters and exclusive means for the prediction of thiolate oxidizabilities and chelate forming properties in order to understand and influence chelation therapy and oxidative stress at the molecular level.
