New Tris(thioimidazolyl)borate Ligands and Some Zinc Complexes Thereof

Abstract

In order to improve the encapsulation of metal ions coordinated by tris(thioimidazolyl)borate ligands, four new such ligands with o-substituted phenyl substituents were synthesised as well as ones with p-tolyl and cyclohexyl substituents. In order to provide a basis for their bioinorganic zinc complex chemistry, they were converted to some zinc-halide, -carboxylate, -nitrate, -phenolate and -benzylate complexes. They

New Polar Pyrazolylborate Ligands and Their Basic Zinc Complex Chemistry

“…In the case of the related sulfurcontaining tripod ligands, there is precedence for the preferred coordination of alcohol and perchlorate ligands. [25,26] The 1 H-NMR spectrum of 1h, just like the spectra for several other complexes of 1, displays a splitting of the pyrazolyl and pyridyl resonances with intensity ratios of 1:5, indicating the presence in solution of a complex with an unknown mode of oligomerization. In the solid state 1h is dimeric, with the two complex units being held together by a pair of bridging pyridine rings that lie across a center of symmetry, see Figure 5.…”

Biomimetic Thiolate Alkylation with Zinc Pyrazolylbis(thioimidazolyl)borate Complexes

“…This was found to be favorable for encapsulation as it induces the phenyl substituents that point away from the zinc centers to rotate such that their ortho positions get placed nearer to the metal. [20] Ligands L 1 and L 2 L 1 has been described by us previously, [17] and L 2 was prepared by the same procedure from equimolar amounts of the thioimidazole and the pyrazole together with KBH 4 in boiling toluene. In order to purify L 2 it had to be subjected to column chromatography over silica gel.…”

Phosphate triester hydrolysis promoted by S3–zinc(II) complexes with a bridged hydroxide: The crystal structure of TtiZn–OP(O)(OC6H4-p-NO2)2, Tti=hydrotris(N-xylyl-2-thioimidazolyl)borate

“…The properties of the tripod ligand potassium hydrotris (N-xylyl-2-thioimidazolyl)borate kTti [4] suggests that it can act with a considerable utility as it can form four-coordinate zinc(II) complexes with additional ligation from one exogenous neutral or anionic ligand, e.g., [TtiZn-X] + (X = HOR) [4], [TtiZn-X] (X = OR and SR) [4][5][6][7][8]. These zinc(II) model complexes have provided important information concerning the structure and the mechanism of (Cys) 3 Zn(II) proteins such as alcohol dehydrogenase and Ada repair protein [1a].…”

“…The crystal structure of TtiZn-OP(O)(OC 6 H 4 -p-NO 2 ) 2 AE 2CH 3 -OH (3) was also reported. To our knowledge, this is the first example of zinc-mediated hydrolysis with S 3 in the coordination sphere capable of promoting phosphoester hydrolysis.The zinc perchlorate complex TtiZn-OClO 3 (1) was obtained by treating the Zn(ClO 4 ) 2 with an equivalent amount of the ligand KTti in methanol [4]. Treatment of the ligand, KTti with equimolar amounts of Zn(ClO 4 ) 2 AE 6H 2 O and KOH in anhydrous methanol under anaerobic conditions followed by a workup and crystallization from 1387-7003/$ -see front matter Ó…”

“…Since the nature of the donor ligand is a commonly employed for providing both structural and mechanistic information [2], it is important to ascertain how biologically relevant ligand complements influence the hydrolytic activity of zinc model complexes. As part of our studies in mimicking the zinc(II) coordination structure as well as the function of the zinc(II) ion at the active site, we have designed and investigated several mononuclear zinc(II) complexes to elucidate the detailed reaction mechanism in these hydrolytic zinc enzymes [3].The properties of the tripod ligand potassium hydrotris (N-xylyl-2-thioimidazolyl)borate kTti [4] suggests that it can act with a considerable utility as it can form four-coordinate zinc(II) complexes with additional ligation from one exogenous neutral or anionic ligand, e.g., [TtiZn-X] + (X = HOR) [4], [TtiZn-X] (X = OR and SR) [4][5][6][7][8]. These zinc(II) model complexes have provided important information concerning the structure and the mechanism of (Cys) 3 Zn(II) proteins such as alcohol dehydrogenase and Ada repair protein [1a].…”