Complexes osmium

Like Ru(bpy)3, Osfbpy) is a kinetically inert coordinately saturated d complex. The difference between the two complexes is that Ru(bpy)3 has a second 

The complex Os(bpy)3 has an excited state lifetime of 19 ns in aqueous solution and excited state potentials of -0.96 V and 0.59 V for (M /M ) and E (M /M ), respectively. This excited state lifetime is considerably shorter than that of Ru(bpy)3, which is to be expected on the basis of spin-orbit quenching and from the excited state redox potentials—Os(bpy)3 is a stronger reductant but a weaker oxidant than is Ru(bpy)3. When one or more of the bpy ligands are substituted by ligands L, systematic changes in the excited state energies and lifetimes can be induced as has been done for the ruthenium analogues.  

Thermal electron transfer reactions of transition metal complexes can result in the product complex being formed in its excited state rather than its ground state. If this product is emissive, light is emitted from this excited state and the reaction is defined as chemiluminescent. Chemiluminescence occurs both in the oxidation of Ru(bpyH and in the reduction of Ru(bpy). The oxidation and reduction steps can be carried out by either a chemical or an electrochemical experiment. If the emissive ions are generated electrochemically on an electrode surface, the reaction is termed electrogenerated chemiluminescence. 

Chemiluminescence from Ru(bpy)i was first observed by treating the oxidized form Ru(bpy) with hydroxide ion - 

Other reducing agents such as N2H4, NaBH4, EDTA, C2O4, and solvated electrons can be used. Chemiluminescence can be observed from the reduced form Ru(bpy)3 by the addition of oxidants such as the 10-methyl phenothiazine radical 

In CH2CI2 solution the present derivative exhibits a reversible one-electron oxidation (E° = -h 0.75 V), centered on the ferrocenyl group (under the same experimental conditions, (C5H5)Fe(C5H4CHO) undergoes reversible oxidation at -1-0.73 V), and an irreversible two-electron reduction ( p = —1.68 V), centered on the triosmium cluster [107]. Spectroelectrochemical measurements seem to indicate that, on removal of one-electron, no important stereochemical changes of the original molecular structure occur [107]. 

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Synthesis. The most important startiug material for synthesis of osmium complexes is OsO. Other important complexes are disodium... 

Iron forms barely any complexes in oxidation states above +3, and in the +8, +7 and +6 states those of ruthenium are less numerous than those of osmium. complexes are confined... 

Vectorial transfer of electronic energy in rod-like ruthenium-osmium complexes with bis-2,2, 2"-terpyridine ligands 97CC333. 

OsCle- is a useful starting material for the synthesis of a range of osmium complexes (Figure 1.4). 

Within the osmium complexes in oxidation states (II-IV) [11,12] the stability of the +4 oxidation state becomes more important. Ammine and tertiary phosphine complexes have been selected for detailed examination. 

Figure 1.60 Syntheses of some osmium complexes of tertiary phosphines.

Considerable structural information is available on osmium complexes of tertiary phosphines, arsines and stibines (Table 1.13) [152, 157]. 

Most of the reports of osmium complexes containing 1,1-dithio ligands are concerned in the use of dithiocarbamate complexes for the analytical determination of the metal (296) a violet color forms when OSO4 and NaR2dtc are mixed in aqueous solution (84). 

Diols are applied on a multimilhon ton scale as antifreezing agents and polyester monomers (ethylene and propylene glycol) [58]. In addition, they are starting materials for various fine chemicals. Intimately coimected with the epoxidation-hydrolysis process, dihydroxylation of C=C double bonds constitutes a shorter and more atom-efficient route to 1,2-diols. Although considerable advancements in the field of biomimetic nonheme complexes have been achieved in recent years, still osmium complexes remain the most efficient and reliable catalysts for dihydroxylation of olefins (reviews [59]). 

Doyle MP (2004) Metal Carbene Reactions from Dirhodium(II) Catalysts. 13 203-222 Drudis-Sole G, Ujaque G, Maseras F, Lledds A (2005) Enantioselectivity in the Dihydroxyla-tion of Alkenes by Osmium Complexes. 12 79-107... 

The reactions of a neutral 10 as well as a cationic dihydrido(acetato)osmium complex 12 with acetylenic compounds were examined (Scheme 6-17) [11-13]. A vinyU-dene 99, an osmacyclopropene 100, or a carbyne complex 101 were obtained, depending on the starting hydrido(acetato) complexes or the kind of acetylene used. In any case, the reaction proceeded by insertion of a C C triple bond into one of the two Os-H bonds, but the acetato ligands do not take part in the reaction and act as stabilizing ligands. 

X10 cm /s. This is over 1,000 X smaller than the Hiffusion coefficient for this osmium complex diffusing freely in the acetonitrile solvent (obtained from the limiting current at the naked Pt electrode), and the observed PD corresponds to a very low permeability of the polymer film to luch bulky permeants. 

N—N=CPh2)],2415 the 1,5-di-p-the nitrido osmium complex 1,4,8,11 -tetra-azacyclotetradecane... 

The potential of osmium complexes as homogeneous catalysts has been highlighted in two recent reviews.100,101... 

In spite of the rich chemistry developed starting from the OsHCl(CO)(P Pr3)2 complex, the presence of a carbonyl group in its coordination sphere is probably a limitation for some subsequent developments. In this context it seems important to mention the encouraging reactivity of the related osmium(IV) complex, OsH2Cl2(P Pr3)2, that in methanol afford OsHCl(CO)(P Pr3)2. We believe that both interrelated osmium complexes present not only a rich chemistry but also a promising future as starting materials in organometallic chemistry. 

The electroactive units in the dendrimers that we are going to discuss are the metal-based moieties. An important requirement for any kind of application is the chemical redox reversibility of such moieties. The most common metal complexes able to exhibit a chemically reversible redox behavior are ferrocene and its derivatives and the iron, ruthenium and osmium complexes of polypyridine ligands. Therefore it is not surprising that most of the investigated dendrimers contain such metal-based moieties. In the electrochemical window accessible in the usual solvents (around +2/-2V) ferrocene-type complexes undergo only one redox process, whereas iron, ruthenium and osmium polypyridine complexes undergo a metal-based oxidation process and at least three ligand-based reduction processes. 

While the tantalum methylene complex 2 reacts with Mel (15), the osmium complex 3 is quite unreactive, suggesting greater nucleo-philicity of the former compound. 

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