Osmium complexes 1,10-phenanthroline

Another interesting application is the study of the kinetics of thermodynamically unfavourable oxidations of a series of iron, ruthenium and osmium complexes with 2,2 -bipyridyl or 1,10-phenanthroline (ML32 ") (equation 28). If E ° for is more positive than E° for the... 

Like mthenium, amines coordinated to osmium in higher oxidation states such as Os(IV) ate readily deprotonated, as in [Os(en) (NHCH2CH2NH2)] [111614-75-6], This complex is subject to oxidative dehydrogenation to form an imine complex (105). An unusual Os(IV) hydride, [OsH2(en)2] [57345-94-5] has been isolated and characterized. The complexes of aromatic heterocycHc amines such as pyridine, bipytidine, phenanthroline, and terpyridine ate similar to those of mthenium. Examples include [Os(bipy )3 [23648-06-8], [Os(bipy)2acac] [47691-08-7],... 

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). 

Tris(diimine)ruthenium(III) complexes are significantly more oxidizing than the analogous complexes of both iron(III) and osmium(III). This correlates well with the observation that rates of reduction in base are also faster for the tris(diimine)ruthenium(III) complexes. The tris(l,10-phenanthroline)ruthenium(III) reduction is significantly faster than the tris(2,2 -bipyridine)ruthenium(III) reduction, and this may be the reason why it is only the latter reaction that has been investigated in detail (1, 2). This system is particularly complex, and the rate law given by Eq. (1) holds only for very small concentrations of ruthenium complex. In contrast to the irondll) systems, simple kinetics... 

A recent development31 is the preparation of metal polymer complexes directly on the electrode via the electrochemically induced polymerization of the metal complex. Ruthenium(II) and osmium(II) complexes with ligands containing aromatic amines, e.g. 3- or 4-aminopyridine or 5-amino-1,10-phenanthroline, are electrochemically polymerized to yield a film of the metal polymer on the electrode surface. The polymerization involves free radicals, which are formed via the initial oxidation of the metal complex to a radical cation and subsequent reaction of the radical cation with a base to yield the free radical. 

Demas et al. described optical oxygen sensors using analogous osmium(II) complexes that have intense red absorptions and that can be excited with low-cost, high-intensity red diode lasers [25]. The osmium(II) complexes are probably more photochemically robust than ruthenium(II) complexes because of the larger energy gap between emitting state and the photochemically destructive upper d-d state. In Table 2, the photochemical and photophysical properties of osmium(II) tris(l,4-diphenyl-l,10-phenanthroline) (Os(dpp)3+) and osmium(II) tris(l,10-phenanthroline) (Os(phen)3+) are indicated as examples of osmium(II) complexes. The luminescence lifetimes of Os(dpp)3+ and Os(phen)3+ are 4.6 and 6.0 ns in dichloromethane solution,... 

Tor modified a 2/-deoxyuridine with an alkynyl moiety at the 5-position of the base, and coupled it to ruthenium(II) and osmium(II) complexes with a 3-bromo-l,10-phenanthroline ligand to produce nucleosides (5) [33]. The ruthenium(II) nucleoside emits at 633 nm with a lifetime of 1.1 ps and a luminescence quantum yield of 0.051 in degassed aqueous solutions, while the osmium(II) analogue shows lower-energy and much weaker emission (A.em = 754 nm, tq = 0.027 ps, (Pcm = 0.0001). Phosphoramidites equipped with these... 

The distortions induced in the DNA double helix by the interstrand cross-links have been characterized by several techniques. As judged by chemical probes (diethyl pyrocarbonate, hydroxylamine, osmium tetroxide), antibodies to cisplatin-modified poly(dG-dC)-poly(dG-dC), natural (DNase I) and artificial (1,10-phenanthroline-copper complex) nucleases, the cytosine residues are accessible to the solvent, and the distortions are located at the level of the adduct [48-50]. From the electrophoretic mobility of the multimers of double-stranded oligonucleotides containing a single interstrand cross-link [50] it is deduced that the DNA double helix is unwound (79°) and its axis is bent (45°). 

One group of NADH oxidants, which does not fit the proposed reaction scheme in Fig. 2.4 are the metal complexes. Examples of this type include nickel hexacyanoferrate deposited on porous nickel electrodes [29], gold electrodes modified with cobalt hexacyanoferrate films [30] and adsorbed l,10-phenanthroline-5,6-dione complexes of ruthenium and osmium [31]. It is unclear how these systems work and no mechanism has been proposed to date. It may be worth noting that dihydronicotinamide groups have been shown to reduce aldehydes in a non-enzymatic reaction when the reaction is catalysed by zinc, a metal ion [15]. In a reaction between 1,10-phenanthroline-2-carboxaldehyde and N-propyl-l,4-dihydronicotinamide, no reaction was seen in the absence of zinc but when added to the system, the aldehyde was reduced and the nicotinamide was oxidised. This implies that either coordination to, or close proximity of, the metal ion activates... 

Chirality effects are also reported in the energy transfer from the ruthen-ium(II) polypyridyl complex to the osmium(II) complex in Langumuir-Blodgett (LB) films [76]. In this experiment, the LB film was prepared with [Ru(dp-phen)3]2+ (dp-phen = 4,7-dipheny 1-1,10-phenanthroline) and stearic acid, where the molar ratio was 1 1 to 1 4. The quenching reaction of the ruthenium(II) complex was carried out with optically pure osmium(II) complex, [Os(dp-phen)3]2+. This reaction consists of photoexcitation of the ruthenium(II) and osmium(II) complexes [Eqs. (29) and (30)], spontaneous decays of the excited ruthenium(H) and osmium(II) complexes [Eqs. (32) and (33)], and the energy transfer between the exited ruthenium(II) complex and the osmium(II) complex [Eq. (31)]. 

Nitrogen is, after oxygen, the most frequently encountered donor atom in the coordination chemistry of osmium. There is a large and growing body of work on the ammine, pyridine, ethylenediamine and porphyrin complexes, but the most popular and rapidly growing field of study at the present time is that of the polypyridyls , the 2,2 -bipyridyl, 1,10-phenanthroline and 2,2,2,6 - terpyridyl complexes of the metal. 

As a tridentate conjugated ligand this would be expected, like 2,2 -bipyridyl and 1,10-phenanth-roline, to stabilize osmium(II) and this is indeed the case, with most of the reported complexes containing divalent osmium. The unsubstituted bis complex [Os(terpy)2]2+ is remarkably stable. It seems likely that terpyridyl complexes of osmium(II) are good candidates for further investigation as photosensitizers, having so far received less attention than the corresponding bipyridyl or phenanthroline species. 

Charton (J52) has also applied the extended Hammett equation to the oxidation-reduction potentials of 5-substituted phenanthroline complexes of iron in various acidic media (95, 97, 651) and of bis-5- and 4,7-substituted phenanthroline complexes of copper in 50% dioxane (404). Thus, one should expect an overall similarity between the variations in pAa, stability constant, and oxidation-reduction potential data for the various ligands. The variations in a and )3 values found for various substitution positions and the tautomerism in the LH+ ions show that the correlation need not be good. A similar point may also be made about the comparison of data for the transoid bipyridylium ions and their cis complexes. Plots of A versus pA for various systems (95, 404) show a linear dependence to differing extents. As would be expected, the data for analogous complexes of iron (28), ruthenium (214, 217, 531), and osmium (111, 218, 220) show very good correlation. The assumption (152) that the effects of substituents are additive is borne out by these potential data, where the changes in potential on methyl substitution are additive (97). 

Extension beyond the dimetallic stage for complexes constructed using 1 was accomplished with both a ruthenium(II)12 and an osmium(II) core in octahedral coordination.18 The peripheral metal sites in each complex (5 and 6) were occupied by ruthenium(II) species, each peripheral site capped by a pair of 2,2 -bipyridyl ligands. (In all of the preparations noted here, the bridges of the multinuclear complexes were formed by simple displacement of monodentate chloride or pyridine ligands by the bridging species which was bidentate in nature toward each metal center.) In addition to 2,2 -bipyridyl, o-phenanthroline (7) and 2,2 6, 2"-terpyrid-ine (8) were used. 

Irradiation at 300 nm in CCl, CHCl, or CH2CI2 promotes am irreversible reaction and formation of what is probably [Os(IV)(TTP)Cl2l. Optimum conditions have been reported for determination of osmium by measurement of the luminescence of its 1 3-complex with 1,10-phenanthroline.A catalyst, prepared by reducing the product of grafting OsO on to the C-C bond of sepiolite, has been found to mediate the photooxidation of water but to do so less efficiently than RuOjj. This is the first exaunple of a dispersed water oxidation catalyst grafted on to a solid support. 

Ruthenium(IIl) and Osmium(Hl) Amine and Ammine Complexes. Only a few amine complexes of Os111 are known, but for Ru111 there are several types and some of their reactions have been given in Fig. 26-F-3. Both elements form 2,2 -bipyridine and 1,10-phenanthroline complexes. 

The level schemes for [Ru(phen)3] and [Os(phen)3] (phen == 1,10-phenanthroline) are representative of the clusters of low lying electronic states that arise from dv configurations of many ruthenium (II), osmium (II), and iridium (III) complexes. They are highly unusual since they have decay parameters that lie between the ranges expected for conventional singlet and triplet states and because of the magnitudes of the splittings themselves. These parameters control the nature of dir" ... 

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... 

R. Leidner and R. W. Murray, Electron-transfer reactions of iron, ruthenium, and osmium bipyridine and phenanthroline complexes at polymer/solution interfaces, J.Am.Chem.Soc., 106 1606 (1984). 

The reduction of a series of substituted tris-(2,2 -bipyridyl) and tris-(l,10-phenanthroline) complexes of iron(iii) and osmium(iii) with hydroxide ion have been studied. The overall reaction... 

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