The coordination chemistry of pyrazole-derived ligands
About: This article is published in Progress in Inorganic Chemistry.The article was published on 2002-05-01. It has received 764 citations till now. The article focuses on the topics: Coordination complex & Pyrazole.
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TL;DR: The 1,2,4-triazole ligands have gained great attention as ligands to transition metals by the fact that they unite the coordination geometry of both pyrazoles and imidazoles, and in addition exhibit a strong and typical property of acting as bridging ligands between two metal centres.
760 citations
TL;DR: In this article, the stereochemical properties of over 120 pyrazole-based chelating ligands, studied by single-crystal X-ray crystallography were analyzed.
426 citations
TL;DR: In this paper, the authors summarized the results reported mainly within the last 10 years, and it is quite clear from the growing number of emerging publications in this field that the possibility to utilize multicomponent technology allows reaction conditions to be accessed that are very valuable for organic synthesis.
Abstract: Multicomponent reactions have gained significant importance as a tool for the synthesis of a wide variety of useful compounds, including pharmaceuticals. In this context, the multiple component approach is especially appealing in view of the fact that products are formed in a single step, and the diversity can be readily achieved simply by varying the reacting components. The eco-friendly, solvent-free multicomponent approach opens up numerous possibilities for conducting rapid organic synthesis and functional group transformations more efficiently. Additionally, there are distinct advantages of these solvent-free protocols since they provide reduction or elimination of solvents thereby preventing pollution in organic synthesis “at source”. The chemo-, regio- or stereoselective synthesis of high-value chemical entities and parallel synthesis to generate a library of small molecules will add to the growth of multicomponent solvent-free reactions in the near future. In this review we summarized the results reported mainly within the last 10 years. It is quite clear from the growing number of emerging publications in this field that the possibility to utilize multicomponent technology allows reaction conditions to be accessed that are very valuable for organic synthesis. Therefore, diversity oriented synthesis (DOS) is rapidly becoming one of the paradigms in the process of modern drug discovery. This has spurred research in those fields of chemical investigation that lead to the rapid assembly of not only molecular diversity, but also molecular complexity. As a consequence multi-component as well as domino or related reactions are witnessing a new spring.
420 citations
TL;DR: In this paper, a comprehensive surwey of the tris(pyrazolyl)alkanes coordination chemistry, based on the nature of the metal, is presented, together with the main synthetic methods and spectroscopic and structural features of this important class of ligands.
371 citations
TL;DR: The chemistry of the pyrazole ring is summarized, and the metal coordination modes adopted by 1H-pyrazoles and their anions are reviewed, highlighting the wide structural diversity in apparently simple main group pyrazolides.
Abstract: This Perspective summarises the chemistry of the pyrazole ring, and reviews the metal coordination modes adopted by 1H-pyrazoles and their anions. Pyrazolide anions are probably the most versatile ligands in coordination chemistry, with 20 different terminal or bridging coordination modes having been identified so far. Metal cluster compounds supported by pyrazolido ligation are surveyed, concentrating on those reported during the past ten years. Highlights include the wide structural diversity in apparently simple main group pyrazolides; luminescence and charge-transfer complexes in coinage metal pyrazolide clusters; the use of robust metal pyrazolide clusters to construct liquid crystals, supramolecular materials and metal–organic frameworks; and supramolecular complexes formed by pyrazolide-supported metallacrowns.
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TL;DR: A syndrome of withdrawal signs developed when the mice were removed from the vapor chamber and could be graded by scoring a characteristic convulsion elicited by handling the animals, which presumably represents the extent of physical dependence.
Abstract: Alcohol was administered to mice by inhalation, over periods of 1 to 13 days. Daily injections of pyrazole stabilized blood alcohol levels and thus maintained a continuous state of intoxication. The empirical relationship between alcohol concentration in the inspired air and that in the blood was determined. A syndrome of withdrawal signs developed when the mice were removed from the vapor chamber. It could be graded by scoring a characteristic convulsion elicited by handling the animals. This score presumably represents the extent of physical dependence. The intensity of withdrawal convulsions increased with duration of exposure to alcohol vapor and with blood alcohol levels. Single episodes of intoxication produced degrees of physical dependence that varied with the total dose of alcohol (blood alcohol level X days). Mild withdrawal signs appeared after a single injection of alcohol, with or without pyrazole treatment. The signs began to appear when the mice were still intoxicated. A dose of alcohol sufficient to produce a moderate degree of physical dependence did not affect the total activity of liver alcohol dehydrogenase. Liver catalase activity was depressed by pyrazole in vivo , but not in vitro .
332 citations
TL;DR: In this article, the structure of the (p-oxo)diiron(III) core was characterized by extensive Raman, resonance Raman and Fourier transform infrared (FTIR) spectroscopic studies.
Abstract: Using either simple ferric salts or the preassembled (p-oxo)diiron(III) anion, (CI,FeOFeCI,) 2-, bridged binuclear complexes ((HB~z,)F~O(O~CR )~F~(HB~Z,)), R = H, CH,, C6H5 and HBpz3 = tri-1-pyrazolylborate ion, were prepared. X-ray crystallographic studies of the acetate and formate derivatives revealed a structure in which the two iron atoms are linked by a p-oxo and two p-carboxylato bridging ligands in a bioctahedral geometry in which the termini are capped by the tridentate tri-1-pyrazolylborate ligands. The geometry of the {Fe20(O2CR),) core of these compounds is nearly congruent with that found in the azidomet forms of the marine invertebrate oxygen transport proteins, hemerythrin and myohemerythrin. The (p-oxo)diiron(III) center is bent, with an average Fe-0 bond length of 1.783 (3) A and an average Fe-0-Fe angle of 124.6 (1)O. The vibrational modes of this center have been characterized by extensive Raman, resonance Raman, and Fourier transform infrared (FTIR) spectroscopic studies of the model complexes and their I8O analogues. The latter were prepared by exchange with I80H2, which is a facile reaction. The asymmetric stretch (vas) occurs at 751 cm-l and is relatively weak. It underlies a strong HBpz3- ligand band and shifts under another such band (to 721 cm-I) in the lSO derivative. This behavior was mapped by difference FTIR spectroscopy. The symmetric stretch and deformation modes occur at 528 and 278 cm-I, respectively. These vibrational features as well as the magnetic exchange properties, ligand field bands in the optical spectrum (695 nm, e 70 MF;l cm-I; -990 nm, e 3.5 MF;l cm-I), and Mossbauer spectroscopic parameters (6 = 0.52 f 0.03 mm/s; AEq = 1.55 f 0.05 mm/s) are compared to those reported for met- and oxyhemerythrin as well as other proteins believed to contain (p-oxo)diiron(III) cores. Proton NMR investigations of (Fe20(02CCH,)2(HBpz3)2) and its deuterated analogues are reported in which the paramagnetically shifted acetate group methyl proton resonances are identified at -10.5 ppm. This assignment should facilitate location of the analogous resonance in the proteins. Cyclic voltammetric studies of ( FelO- (02CCH3)2(HBp~3)2) revealed an irreversible reduction accompanied by formation of mononuclear (Fe(HBpz,),), which itself undergoes a reversible one-electron oxidation. The instability of the (p-oxo)diiron(II) unit in the model compound parallels that of the reduced (deoxy) form of the protein. Magnetic susceptibility measurements on a SQUID susceptometer over the range 2.9 < T < 300 K revealed the diiron(II1) center of (Fe20(02CCH3)2(HBpz3)2) to be antiferromagnetically coupled with a spin exchange coupling constant J = -121 cm-I, a value close to that (-134 cm-') of methemerythrin.
237 citations
212 citations