Osmium complexes carbonates

The osmium-carbyne carbon bond lengths for the three complexes do not differ significantly, and reference to Table IV indicates that these distances are distinctly shorter than the characterized metal-carbon double bonds of osmium carbene and carbonyl complexes. In both osmium alkylidene and carbyne complexes, then, the metal-carbon multiple bond lengths are largely insensitive to changes in the metal electron density (cf. Section IV,B). 

A similar polymer, composed of osmium complexed with bis-dichlorobipyridine, chloride, and PVI in a PVI—poly(acrylamide) copolymer (Table 2, compound 3), demonstrated a lower redox potential, 0.57 V vs SHE, at 37.5 °C in a nitrogen-saturated buffer, pH 5 109,156 adduct of this polymer with bilirubin oxidase, an oxygen-reducing enzyme, was immobilized on a carbon paper RDE and generated a current density exceeding 9 mA/cm at 4000 rpm in an O2-saturated PBS buffer, pH 7, 37.5 °C. Current decayed at a rate of 10% per day for 6 days on an RDE at 300 rpm. The performance characteristics of electrodes made with this polymer are compared to other reported results in Table 2. 

The electroreduction of some typically inorganic compoimds such as nitrogen oxides is catalysed by the presence of polymeric osmium complexes such as [Os(bipy)2(PVP)2oCl]Cl, where bipy denotes 2,2 -bipyridyl and PVP poly(4-vinylpyridine). This polymer modifies the reduction kinetics of nitrite relative to the reaction at a bare carbon electrode, and provides calibration graphs of slope 0.197 nA with detection limits of 0.1 pg/mL and excellent short-term reproducibility (RSD = 2.15% for n = 20). The sensor performance was found to scarcely change after 3 weeks of use in a flow system into which 240 standards and 30 meat extracts were injected [195]. 

Osmium tetroxide reacts with phenyl Grignard reagent to produce a reactive intermediate, serving as a synthetic route to prepare polyphenyl osmium complexes. For example, reaction with o-tolyl magnesium bromide, o-tolMgBr, forms a purple, tetracoordinated osmium ort/io-tolyl complex, Os(o-tol)4, which reacts with trimethylphosphine or carbon monoxide to yield osmium n-aryl complexes. 

Figure 10 Plot of rate constants for back electron transfer from Sn02 to electrostatically bound ruthenium ( ) and osmium ( ) complexes as a function of the number of carbon atoms comprising alkyl spacers. Within experimental error, the driving force for each series of reactions is unaffected by changing the size of the alkyl spacer.

Miscellaneous. Aside from the oxidation chemistry described, only a few catalytic applications are reported, including hydrogenation of olefins (114,115), a, [3-unsaturated carbonyl compounds (116), and carbon monoxide (117) and the water gas shift reaction (118). This is so owing to the kinetic inertness of osmium complexes. A 1% by weight osmium tetroxide solution is used as a biological stain, particulady for preparation of samples for electron microscopy. In the presence of pyridine or other heterocyclic amines it is used as a selective reagent for single-stranded or open-form B-DNA (119) (see Nucleic acids). Osmium tetroxide has also been used as an indicator for unsaturated fats in animal tissue. Osmium tetroxide has seen limited if controversial use in the treatment of arthritis (120,121). 

Arene ruthenium and osmium complexes play an increasingly important role in organometallic chemistry. They appear to be good starting materials for access to reactive arene metal hydrides or 16-electron metal(O) intermediates that have been used recently for carbon-hydrogen bond activation. Various methods of access to cyclopentadienyl, borane, and carborane arene ruthenium and osmium complexes have been reported. 

Osmium forms a wide variety of alkyl and aryl complexes including homoleptic alkyl and aryl complexes and many complexes with ancillary carbonyl (see Carbonyl Complexes of the Transition Metals), cyclopentadienyl (see Cyclopenta-dienyl), arene (see Arene Complexes), and alkene ligands (see Alkene Complexes). It forms stronger bonds to carbon and other ligands than do the lighter elements of the triad. Because of this, most reactions of alkyl and aryl osmium complexes are slower than the reactions of the corresponding ruthenium complexes. However, because osmium is more stable in higher oxidation states, the oxidative addition (see Oxidative Addition) of C-H bonds is favored for osmium complexes. The rate of oxidative addition reactions decreases in the order Os > Ru Fe. 

CH2BU or p-MeCjH4]. The reaction is considered to be charge controlled and to proceed via electrophilic attack by Sg on the carbyne carbon (178). An additional complex (267, M = W, E = S, L = CO, R = Me) can be obtained from [W=CMe(Cp)(CO)2] and cyclohexenesulfide (179). With the osmium complex 268 (R = /7-tolyl), however, reaction with sulfur does not proceed beyond the t/ -thioacyl complex (269, E = S or Se). Seleno-and telluroacyl complexes result from analogous reactions (180). 

The osmium carbyne complex 115 reacts with elemental sulfur, selenium, and tellurium to afford the complexes 135 in which the element atoms "bridge the metal-carbon triple bond [Eq. (123)] (56). Complex 115 also reacts with transition metal Lewis acids such as AgCl or Cul to give dinuclear compounds with bridging carbyne ligands. Reaction with elemental chlorine results in addition across the metal-carbon triple bond to generate the chlorocarbene osmium complex 136 [Eq. (124)]. 

CF3H, Methane, trifluoro-cadmium complex, 24 55 mercury complex, 24 52 CF3NOS, Imidosulfurous difluoride, (fluorocarbonyl)-, 24 10 CH2, Methylene ruthenium complex, 25 182 CH2CI4P2, Phosphine, methylenebis-(dichloro)-, 25 121 CH3, Methyl cobalt complexes, 23 170 mercury complexes, 24 143-145 platinum complex, 25 104, lOS CNO, Cyanato silicon complex, 24 99 CN2OS2, l,3k, 2,4-Dithiadiazol-5-one, 25 53 CO, Carbon monoxide chromium complexes, 21 1, 2 23 87 cobalt complex, 25 177 cobalt, iron, osmium, and ruthenium complexes, 21 58-65 cobalt-osmium complexes 25 195-197 cobalt-ruthenium cluster complexes, 25 164... 

OC, Carbon monoxide chromium complex, 21 1, 2 chromium and tungsten complexes, 23 27 cobalt complex, 25 177 cobalt complexes, 23 15-17, 23-25 cobalt, iron, osmium, and ruthenium complexes, 21 58-65 cobalt-osmium complexes, 25 195-197 cobalt-ruthenium cluster complexes, 25 164... 

The first p3—if type to be structurally characterized was an osmium cluster anion. Caulton et al.17 reported a rhodium/osmium complex which has the carboxylate carbon bound to osmium and each oxygen bound to different rhodium centers. Cutler et al.24 characterized additional complexes of this type. Few examples exist of the other two structural types. 

Iron complex (55) also reacts with H2 to produce methane and ethene to afford propene <80JA1752>. Both reactions appear to involve insertion into a metal-carbon bond followed by elimination. When osmium complex (56) adds ethene, the diosmacyclopentane which results from ethene addition is isolated. When terminal alkynes react with (55), an alkene-substituted ring carbon results... 

Polymers containing all metal backbones of Ru-Ru or Os-Os bonds have been prepared via the electrochemical reduction of ruthenium and osmium complexes containing /ram-chloride ligands.81,82 Scheme 2.6 shows the synthesis of polymers with their backbones comprised solely of metal-metal bonds. The polymers were prepared by reducing [Mn(/ran.s-Cl2)(bipyXCO)2] (M = Ru, Os), 33, to M° complexes and forming the polymer after the loss of the chloride ligands. In both cases, the polymers were selective for the reduction of carbon dioxide. 

Formation of Ru ri3-CH2CHCHCH=C(CH3)2 Cl(CO)2(P Pr3) Formation of monothio-P-diketonato derivatives The hydride-chloro-osmium complex OsHCl(CO)(PTr3)2 as a precursor for carbon-carbon, carbon-oxygen, and carbon-sulfur coupling reactions... 

In contrast to the reaction with phenylacetylene, the treatment of 190 with 2 equiv of methyl propiolate leads to the alkenyl-alkynyl compound 200 (Scheme 55). The use of a 1 1 molar ratio of alkyne to osmium complex gives the same product along with unreacted dihydride-dihydrogen complex [79]. The addition of a toluene solution of HCl to a toluene solution of 200 produces the carbon-carbon coupling of the alkynyl and alkenyl fragments to give selectively the... 

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