Complexes with zinc compounds

An example of thione coordination is demonstrated with the thiocarbonyl donor ligand 2,6-dimethyl-4H-pyran-4-thione, that gives a complex with zinc chloride of the form ZnL2Cl2-The crystal structure shows the zinc is tetrahedrally coordinated by two chloride and two sulfur donors and the compound was further studied by 3H NMR and IR spectroscopy.573 Both monomeric and dimeric heterocyclic thione complexes have been formed with zinc.5 4,575... 

A porphyrin compound with a 2,9-dimethyl- 1,10-phenanthroline functionality fused at the beta-pyrrole positions is a phthalocyanine analog, and formed a complex with zinc in the cavity and a further zinc binding to the phenanthroline group. The absorption and emission spectra of the compound with and without the external zinc demonstrated the strong effects of the second metal binding on the porphyrin 7r-system.840... 

Pentadentate ligands with N4S donors based on methyl 2-aminocyclopent-l-ene-l-dithiocar-boxylate with pendent pyrazolyl groups (113) form complexes with zinc including a structurally characterized trigonal-bipyramidal zinc compound.891... 

Both of the above approaches employed a metal ion as a template about which the corrin cyclization was performed, but the nickel or cobalt ions could not subsequently be removed. In order to obtain metal-free corrins, a new route was therefore devised (67AG865) which employed the novel principle of sulfide contraction (Scheme 22). Thus the sodium salt of the precorrin (284) (Scheme 23) was transformed into the thiolactam (285), and loose complexation with zinc(II) ions caused cyclization to give (286), which was treated with benzoyl peroxide and acid to give the ring-expanded compound (287). Contraction with TFA/DMF gave the corrins (288) and (289), and the major of these (289) was desulfurized with triphenylphosphine and acid to give (288). Finally, demetallation with TFA gave the required metal-free corrin (290), a source for a whole variety of metal derivatives. 

HLADH was applied for the reduction of a broad variety of substrates. The regeneration of NADH can be achieved by the ethanol coupled-substrate method [239]. Cyclic ketones are good substrates for this enzyme [137, 240, 241]. Heterocyclic compounds containing oxygen or sulfur are accepted, too [242 246], but nitrogen-containing substrates are inhibitors of HLADH, because they apparently complex with zinc in the active site of the enzyme [247],... 

An operational description is that one reactant (the more ionic compound with the more electropositive metal) transfers alkyl anions to the other. Thus the four methyl groups in Li2BeMe4 form a distorted tetrahedron around the beryllium, with longer distances to the lithium ions. However, this description is oversimplified. The low-temperature nuclear magnetic resonance (NMR) spectrum of Li3MgMe5 has three different methyl resonances, suggesting structure (14), related to the MeLi tetramer. Ate complexes with zinc and aluminum compounds also form. Electron-deficient bridge-bonded structures, exemplified by the X-ray structure of... 

Intramolecular A dduct Formation. By analogy with zinc compounds, the incorporation of donor atoms in the alkyl groups of R2Cd derivatives may result in the formation of intramolecular adducts. For example, the pyridyl group in the complex [(NC5Fl4)(SiMe3)2C]2Cd (7) coordinates to the Cd center [d(CA-C) = 2.21 k, 4(Cd-N) = 2.49A C-Cd-C = 174.3° N-Cd-N = 108.9°]. ... 

A variety of reducing agents have been used to reduce nitroarenes to azo compounds. However, a mixture of zinc and sodium hydroxide is used most frequently. - Reduction under these conditions produces hydrazo compounds, which are then oxidized to azo compounds by dissolved atmospheric oxygen alternatively, air can be drawn through the product solution to achieve the conversion. - Occasionally, activation of the zinc dust is required prior to its use, and, since metal ions form chelated complexes with azo compounds, a vigorous post-treatment with acids is recommended. The zinc-sodium hydroxide reduction conditions are sufficiently mild that p-nitrostyrene (2 equation 2), can be reduced without reduction of the vinyl groups. ... 

In this test the tea-making procedure is standardised for the purpose of finding out if different amounts of manganese and zinc are released into the infusion from different types of tea. Tea leaves may contain large amounts of manganese and zinc but only relatively small proportions get into the infusion. Most of the metallic elements remain as insoluble complexes with organic compounds in the leaves. However, tea may still be an important dietary source of manganese and zinc. 

Screttas and Eastham found that this base forms crystalline complexes with organometallic compounds of magnesium, lithium, and zinc. Thus on addition of a benzene solution of TED to a solution of butyllithium a crystalline complex separates the composition is BujLij —TED-Bu Lia. Triethylamine (1) and quinu-clidine (2) form similar complexes but they are considerably more soluble than the corresponding TED complex. 

Not only complexes but also metal salts that complex with the compounds to be separated can be used as selective complexing stationary phases. For example, Phillips [91] described the use of zinc and copper stearates and nickel oleate for the selective separation of amines. The retentions of aliphatic amines decrease in the order primary > secondary > tertiary. The separation of 7-picoline and 2,6-lutidine on a zinc stearate column is possible if the column efficiency is only 4 theoretical plates and the column is 1 cm long. To effect this separation on a non-selective silicone stationary phase a column with an efficiency of 250,000 theoretical plates is required. Some amines (e.g., ethanolamine... 

Commonly, polymers with a poly(siloxane) backbone and pendant side chain liquid crystalline groups are used. The side chain liquid crystalline groups are organic complexes with zinc, nickel, or crown ethers. This type of polymers is addressed as mesomorphic poly(siloxane). Side chains based on 4-biphenyl-4-allyloxybenzoate exhibit a special separation performance for racemic compounds. ... 

This route has now led to the formation of a trefoil knot using either esterification or RCM of appendages to the alcohol functions. The ester functions are rather unstable, but the compound formed by RCM allows the removal of the templating zinc ion, giving the free knot. This ligand forms much more stable complexes with zinc(II) than the precursor linear complex, which is a characteristic trait of topologically nontrivial ligand systems. 

A red fluorescent coordination polymer (32) was obtained by our research group from a tpy-functionalized perylene bisimide chromophore by complexation with zinc triflate [85]. The polymer 32, which is readily soluble in chloroform/methanol mixtures and DMF, retains the excellent fluorescence properties of the free ligand and shows reversible binding, thus, the chain length decreases upon addition of an excess amount of Zn . The polymeric structure was estabhshed by NMR using a dimer model compound as reference as well as by DOSY NMR, UV/vis spectroscopy, fluorescence anisotropy measurements, and AFM [86]. Further superstructures were ob-... 

The mechanisms of these reactions bear marked similarities, in spite of the differences in their reactivities and selectivities. Thus, in certain cases, a four-membered intermediate similar to the 1,2-oxaphosphetane intermediate in the Wittig reaction appears in the Peterson reaction as a pentacoordinate 1,2-oxasiletanide. Reactions of transition metal carbene complexes with carbonyl compounds also proceed through the formation of a four-membered oxametallacycle, which was recently found to be an intermediate of some McMurry reactions. Carbonyl olefination utilizing dimetallic species of zinc or chromium is somewhat similar to the Julia reaction in that they both involve the process of ) -elimination. 

The presence of alkaloids containing one or two imidazole nuclei is the main feature of the genus Leucetta, and several of these compounds exist in the form of a complex with zinc ion (see Chapter 3). The main results on the genus Leucetta are summarized in Table 19.3. 

This complex has also been defined with a n < 8 composition. Kim and Bae, studying the phases of this system over the concentration range 0.05-0.5 (mass fraction of salt), considered the existence of a semicrystalline complex with n < 8 stoichiometry, which agrees with the above results. Ko and colleagues also found an intermediate compound with n < 8, in a study of a hyperbranched polymeric system based on polyols complexed with zinc iodide. In a more recent study, for more diluted electrolytes of the PEO-Znl2 system, with n = 12 and n = 16, a crystalline complex was also found to exist alongside the pure PEO." ... 

Zn — Zn in acid solution —0-76 volts) Apart from possible Zn and Zn2 in some melts all zinc compounds are in the +2 state, generally in octahedral or tetrahedral co-ordination. Readily forms complexes, particularly with O and N ligands. 

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