Tris complexes reduction

Dimroth rearrangement, 5, 438 Imidazolium chloride, 4-chloromethyl-reaction with poly(vinyl alcohol), 1, 306 Imidazolium chloride, 2,4,5-tri(diethylamino)-reduction, 5, 415 Imidazolium complexes, 7, 746... 

A basic solution with a large excess of acetylacetone is strong blue. Complexes have been studied (log Pi = 5.383, log j82 = 10.189, log / 3 = 14.704). A potential of —1.0 V vs. SHE was measured for the reduction of the VUI tris complex.84 Mixed complexes V(L)2(py)2(L= acac, trifluoroacetylacetonato or dibenzoylmethanato) isolated from solutions containing VS04 and the appropriate ligand97 show intense absorption in the region 700-300 nm. 

Malonic acid CH2(C02H)2 (H2mal) (209) has a coordination chemistry with chrommm(III) closely resembling that of oxalate. Malonic acid is a slightly weaker acid than oxalic acid and slightly more labile complexes are formed. The tris complex is the most extensively studied, prepared by the reduction of chromate solutions or the reaction of chromium(III) hydroxide with malonate.917,918 919 The cis and trans diaqua complexes may be prepared by the reduction of chromate with malonate the isomers are separated by fractional crystallization. The electronic spectrum of the tris complex is similar to that of the tris oxalate and a detailed analysis of these spectra has appeared.889... 

Reaction of 0s04 with catechol or substituted catechols Rcat in chloroform yields the deep blue diamagnetic Os(Rcat)3 species (Rcat = catechol, 4-rerf-octyl-, 4-terr-butyl-, 3,5-di-ferf-butyl-catech-ol).486 X-Ray crystal structures of Os(cat)3 and of the tris complex with 3,5-di-terf-butylcatechol show these to have D3 symmetry the Os—O distances fall within the range 1.947 to 1.985 A (mean 1.960 A) and the C—O distances are between 1.30 and 1.35 A the catecholato (02C6H4 or 02C6H2) rings are essentially planar.666 For Os(cat)3, IR, Raman, HNMR and electrochemical data were obtained the latter showed two one-electron reversible reductions, presumably to [Os(cat)3] and [Os(cat)3]2-. The diamagnetism of these formally osmium(VI) species probably arises from the distortion from octahedral to Z>3 symmetry.486... 

The most comprehensive studies of the effect of acidity on potentials are those of Schilt 617, 618), where media up to 12 M in sulfuric acid were used. For M = Fe, Ru, or Os, the oxidation-reduction potential for M(bipy) +/M(bipy) + becomes less negative as the medium becomes more acid, while the converse is true for [M(bipy)2(CN)3]/[M(bipy)2(CN)2]. These results are interpreted as showing the formation of stable ion-pairs derived from the tris complexes and acid anions the CN groups in the mixed M(II) but not M(III) complexes may behave as bases yielding mono- and diprotonated species. 

There are few reported data for the rates of electron transfer between the large complexes of these ligands. The rates are very large, and for the iron group metals NMR studies only allow a lower limit of 10 1 mole sec to be set (200, 224, 473, 474). The exchange between the tris complexes of Co(II) and Co(III) is found to catalyze ligand exchange for Co(III) (230) it has also been studied in nonaqueous media (504). Because of their convenient analytical properties, however, bipyridyl and phenanthroline complexes have been extensively examined in their oxidation reduction reactions. 

Bipyridine is a strong field ligand that forms relatively stable complexes, with the inherent M—N bond strength enhanced by the chelate effect. These factors favor the formation of 4-coordinate bis and 6-coordinate tris complexes. The tris complexes of the first row transition metals in normal oxidation states (+2 or +3) are best prepared by the reaction of a suitable metal salt with an excess of bpy in water, methanol, or other organic solvent. The solid complexes can be obtained by crystallization or by the precipitation of the perchlorate, hexafluorophosphate, tetrafluoroborate, or other salts. Because bpy is a strong field ligand, the lower oxidation states tend to be favored, and reduction of M(III) complexes can occur in these preparations. The M(III) complexes are usually readily obtained by the chemical, aerobic, or electrochemical oxidation of the M(II) species. 

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