Tris-phenanthroline metal oxidants

Homogeneous Processes with Tris-phenanthroline Metal(III) Oxidants. The rates of electron transfer for the oxidation of these organometal and alkyl radical donors (hereafter designated generically as RM and R, respectively, for convenience) by a series of tris-phenanthroline complexes ML33+ of iron(III), ruthe-nium(III), and osmium(III) will be considered initially, since they have been previously established by Sutin and others as outer-sphere oxidants (5). 

Chemical or photochemical oxidation of a nucleic acid is accomplished very efficiently by a variety of metal complexes. In the presence of hydrogen peroxide and thiol, bis(phenanthroline) cuprous ion very efficiently cleaves DNA (26). Tris(phenanthroline) complexes of cobalt(IIl) or rhodium(III) promote redox reactions in their excited states (27, 28). These photoac-tivated probes bind to the DNA helix in a fashion comparable to the spectroscopic probes described above and then, upon photoactivation, promote DNA strand cleavage. 

It is worthwhile to analyze why co-existing soft ligands assist low oxidation numbers. If we want to make a copper(I) compound, it is very difficult to try the aqua ion, the fluoride or the anhydrous sulphate because they disproportionate to the metallic element and a higher oxidation state, here Cu(II). However, as seen in Eq. (7) it is easier to make the ammonia complex Cu(NH3)2 under anaerobic conditions, and even easier to make copper(I) complexes of pyridine and of conjugated bidentate ligands such as 2,2 -dipyridyl and 1.10-phenanthroline. The experimental problems are reversed in the case of iodides and cyanides, where it is easy to precipitate Cul or CuCN or to prepare solutions in an excess of the ligand containing Cul J,... 

Hence, the first clearcut evidence for the involvement of enol radical cations in ketone oxidation reactions was provided by Henry [109] and Littler [110,112]. From kinetic results and product studies it was concluded that in the oxidation of cyclohexanone using the outer-sphere one-electron oxidants, tris-substituted 2,2 -bipyridyl or 1,10-phenanthroline complexes of iron(III) and ruthenium(III) or sodium hexachloroiridate(IV) (IrCI), the cyclohexenol radical cation (65" ) is formed, which rapidly deprotonates to the a-carbonyl radical 66. An upper limit for the deuterium isotope effect in the oxidation step (k /kjy < 2) suggests that electron transfer from the enol to the metal complex occurs prior to the loss of the proton [109]. In the reaction with the ruthenium(III) salt, four main products were formed 2-hydroxycyclohexanone (67), cyclohexenone, cyclopen tanecarboxylic acid and 1,2-cyclohexanedione, whereas oxidation with IrCl afforded 2-chlorocyclohexanone in almost quantitative yield. Similarly, enol radical cations can be invoked in the oxidation reactions of aliphatic ketones with the substitution inert dodecatungstocobaltate(III), CoW,20 o complex [169]. Unfortunately, these results have never been linked to the general concept of inversion of stability order of enol/ketone systems (Sect. 2) and thus have never received wide attention. 

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. 

A number of transition metals can be determined conveniently if their cations undergo a definite change of oxidation state see Oxidation Number) on titration with a standard solution of potassium permanganate, potassium dichromate, cerium(IV) sulfate, or ammonium hexanitratocerate(IV). Several visual indicators have been proposed, including diphenylamine and its derivatives, xylene cyanole FF, and especially A-phenylanthranilic acid and tris(l,10-phenanthroline)iron(II) sulfate ( ferroin ). Solutions of have been used in the determination of iron, copper, titanium, vanadium, molybdenum, tungsten, mercury, gold, silver, and bismuth, and standard solutions of and Sn F U, and and Mo have also... 

Osmium, quinuclidinetetraoxime-stereochemistry, 44 Osmium, tetrachloronitrido-tetraphenylarsenate stereochemistry, 44 Osmium, tris( 1,10-phenanthroline) -structure, 64 Osmium(II) complexes polymerization electrochemistry, 488 Osmium(III) complexes magnetic behavior, 273 Osmium(lV) complexes magnetic behavior, 272 Osmium(V) complexes magnetic behavior, 272 Osmium(VI) complexes magnetic behavior, 272 Oxaloacetic acid decarboxylation metal complexes, 427 Oxamidoxime in gravimetry, 533 Oxidation-reduction potentials non-aqueous solvents, 27 Oxidation state nomenclature, 120 Oxidative addition reactions, 282 Oxidative dehydrogenation coordinated imines, 455 Oximes... 

Table 3 Rate constants for the oxidation of non-metallic substrates by derivatives of tris-(UlO-phenanthroline)iron(m) at 20 °C...

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