Salicylate ligands

The complexes of aromatic hydroxy carboxylic acids (salicylic acid and its isomers) with [Bu2Sn(IV)] and [Ph3Sn(IV)] were obtained. The FT-IR and Raman spectra clearly demonstrated that the organotin(IV) moieties react with the O, O) atoms of the ligands. It was found that in most cases the -COO group chelated to the central atoms, but monodentate coordination was also observed. The complexes probably have polymeric structures. 

The case of the disalicylate, 1-methyl trimethylene disalicylate, is interesting. Because of steric hindrance it is unlikely that the two salicylate ligands can chelate to one calcium atom. In theory the disalicylate... 

Merola reported the preparation of hydrido(carboxylato)iridium(lll) complexes, mer-[lrCl(0C(0)R)(H)(PMe3)3] (90) (R = Ph, Me), by oxidative addition of acetic acid or benzoic acid to [Ir(cod)(PMe3)3]Cl (67) [46]. The structure of 90 (R = Ph) in which the carboxylato ligand coordinates as an T -ligand, was confirmed by X-ray analysis. The reaction of 67 with salicylic acid yielded the product 91, which resulted from activation of the O-H bond of the carboxylato but not of the hydroxo group (Scheme 6-13). 

The N,N-diethylamide of salicylic acid is a useful ligand in conjunction with Cul and permits amination of aryl bromides by primary alkylamines.151... 

Thanks to the presence of the fluorine substituent on the salicylic ring, the 19F NMR measurements could be performed. Similar values of the chemical shifts for the ligand ( 75.2 ppm) and the complexes (from 70.2 up to — 72.8 ppm) suggested that the fluorine atom was not involved in bonding. 

Fig. 25. Protonation and ligand dissociation mechanism for 0-TRENSOX (26) (176). (A) Four-step hydrolysis mechanism of O-TRENSOX where Q represents 8-hydroxyquinolyl and S the corresponding salicylate coordinating moiety. Charge on the complex has been omitted for clarity. (B) Schematic representation of the salicylate shift of the 8-hydroxyquinolyl donor groups of O-TRENSOX.

The interaction of ligands derived from salicylic acid and its derivatives has been extensively investigated (83, 147, 149, 160, 170, 176, 183-205). A similar situation obtains with regard to l-hydroxy-2-naphthoic acid (185, 194, 196, 198, 206-215). Salicylic acid derivatives may be useful in chelation therapy for beryllium poisoning (2). 

This compound can be considered as a derivative of the hydrolysis product, [(H20)3Be(0H)Be(H20)3]3+, in which the bidentate 3-methyl-salicylate ligands each replace two water molecules, the other two water molecules being replaced by a carbonate ion bridging between two beryllium atoms. Similar carbonate bridges have been proposed previously (132). 

Hayashi et al.147 reported another highly enantioselective cyanohydrination catalyzed by compound 138. In this reaction, a Schilf base derived from fl-amino alcohol and a substituted salicylic aldehyde were used as the chiral ligand, and the asymmetric addition of trimethylsilylcyanide to aldehyde gave the corresponding cyanohydrin with up to 91% ee (Scheme 2-56). 

In a bidentate ligand system, three molecules of a dye containing either a terminal salicylic acid unit (as in 5.2) or an o-nitrosonaphthol residue are able to chelate simultaneously with a trivalent metal ion of CN6, such as chromium (III) or iron(III), to form a 1 3 metal-dye complex (as in 5.8). Historically, the most important bidentate ligand system was alizarin (5.1). It has been suggested that both hydroxy groups and the keto group in the peri position are all involved with the metal atom in the chelation mechanism. 

The coupling of Naphtol AS or its phenyl-substituted derivatives with diazonium salts from variously substituted anilines in aqueous alkaline solution (section 4-11) gave incomplete reactions and impure products in some instances, probably because these coupling components have inadequate solubility in aqueous media. Pure dyes in ca. 90% yields were obtained by reaction in dimethylformamide in the presence of sodium acetate. Metallisation of these o,o -dihydroxyazo ligands with sodium chromium salicylate or a cobalt(II) salt gave metal-complex dyes in 80-100% yields [22]. Specific structural isomers of these complexes were identified by i.r., n.m.r., Raman and UV/visible spectroscopy [23]. 

Many copper(II) complexes, including Cu(DIPS)2 (DIPS = diisopro-pylsalicylate), Cu(salicylate)2, and Cu(Gly-His-Lys), are also active in superoxide dismutation (437, 438), but their use in vivo is limited by dissociation of Cu(II) and binding to natural ligands such as albumin (439). In contrast, the activity of Fe-93 is not affected by albumin (439, 440). 

Bismuth compounds have been used for treating gastrointestinal disorders for more than two centuries (451). These include bicarbonate, nitrate and salicylate salts, and colloidal bismuth subcitrate. These are all Bi(III) compounds Bi(V) is usually a strong oxidant. Their structures are largely unknown and often contain a mixture of anionic ligands. This reflects the strong tendency of Bi(III) to hydrolyze and form stable hydroxo and oxo complexes. The first pKa of Bi(III) in water is ca. 1.5. Bismuth(III) has a variable coordination number, from 3 to 10. 

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