Detail of "27006-76-4"

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Zinc(II) N2S2 Schiff-base complexes incorporating pyrazole: syntheses, characterization, tautomeric equilibria and racemization kinetics

Zinc(II) N2S2 Schiff-base complexes incorporating pyrazole: syntheses, characterization, tautomeric equilibria and racemization kinetics. Anderson, Oren P.; la Cour, Agnete; Findeisen, Matthias; Hennig, Lothar; Simonsen, Ole; Taylor, Lucille F.; Toftlund, Hans (Department Chemistry, Colorado State University, Fort Collins, CO 80523, USA). Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry, (1), 111-120 (English) 1997 Royal Society of Chemistry. CODEN: JCDTBI. ISSN: 0300-9246. DOCUMENT TYPE: Journal CA Section: 78 (Inorganic Chemicals and Reactions) Section cross-reference(s): 67, 75 Chiral four-coordinate Zn(II) N2S2 complexes with bi- or tetradentate Schiff base ligands were prepd. and their properties studied by spectroscopic methods. The single crystal structures were detd. for two different cryst. modification of bis[4-(2,6-dimethylphenyliminomethyl)-1-methyl-3-phenylpyrazole-5-thiol ato-N,S]zinc(II) 1, a triclinic modification (1a) and an orthorhombic one (1b), and for bis(4-isopropyliminomethyl-3-methyl-1-phenylpyrazole-5-thiolato-N,S)zi nc(II) 2. The coordination geometry of 1 is similar to that found for the active site of horse liver alc. dehydrogenase. The asym. units in the structures of 1 contain two pseudo-tetrahedral complexes slightly distorted towards trans-planar coordination geometries; the angles q between the N-Zn-S and S'-Zn-N' planes are 97.Several reagents with their cas registry numbers 27006-76-4 and 187097-31-0 are used here.0 and 96.8 (modification 1a), 92.5 and 98.6° (1b) for the two mols., resp. The structure of 2 also reveals a pseudotetrahedral geometry and a slight distortion towards a cis-planar coordination (q = 82.63°) typical of MIIN2S2 complexes. The racemization kinetics (intramol. rearrangement) for the process D J L (or R J S) were studied for four complexes by temp. dependent 1H NMR spectroscopy and the action parameters derived for 1 [DHG = 80.7 kJ/mol-1, DSG = -2.9 J K-1 mol-1, DGG (25°) = 81.6 kJ mol-1] and 2 [DHG = 67.2 kJ mol-1, DSG = -57.8 J K-1 mol-1, DGG (25°) = 84.4 kJ mol-1]. The complexes carrying tetradentate ligands do not racemize <90°. The tautomeric equil. for the protonated pro-ligands and the preferred mesomer of the complexes were studied by NMR and UV spectroscopy. The pro-ligands are mainly in the thione form, while the ligands are thiolate-like when coordinated to Zn(II). The evolution of the electronic spectra with time, however, reveals the development of thiol- or thiolate-like forms for both pro-ligands and complexes. .